Abstract: Studying changes in soil humus composition and humic acid (HA) structural characteristics caused by agronomic practices provide insights into the pathways of soil organic carbon (C) stabilisation dynamics. This five-year field study evaluated the effects of straw returning modes on humus composition and HA structure. Treatments included (i) corn straw returned on the soil surface (NTS), (ii) corn straw incorporated into soil within 0–10 cm (MTS), (iii) corn straw incorporated into soil within 0–20 cm (CTS) and (iv) no corn straw applied (CT). Soil HA was characterised by Fourier transform infrared (FTIR) and fluorescence spectroscopies. The results demonstrated that corn straw returning improved humus C fractions in this order NTS > MTS > CTS > CT in 0–20 cm depth. The FTIR and fluorescence results demonstrated that corn straw returning enhanced aliphatic, hydroxyl, methoxyl and carboxyl groups and simplified HA molecular structure, indicating regenerated and newly formed HA. Among all treatments, NTS was more conducive in simplifying HA molecular structure and enhancing aliphatic and hydrophobic C. Hydrophobicity in aliphatic C is the driving force in the stabilisation of soil C, which is important for sustainable agriculture. Therefore, we conclude that NTS is the better practice to turn arable lands into a sink for C.

Abstract: The primary features of an effective and efficient furrow opener include controlled soil disturbance and low draught and vertical force requirements. When integrated in a no-tillage seeding system, furrow openers should also have the ability to assist, and not hinder, the functions of seeding system components – such as maintaining adequate surface residue distribution, accurate and uniform placement of seeds and fertiliser, and regular inter-plant spacing. This review highlights how these goals are affected by opener type, geometry and settings, and soil and residue conditions. Typically, tine openers cause greater soil disturbance than disc openers whereas disc openers are likely to cause residue hairpinning. Winged tine openers reduce residue interference with seed placement and support greater lateral seed spread. Inverted-T openers can achieve subsurface soil shattering, which helps conserve moisture and provides good seed–soil contact. A tine opener with concave cutting edge reduces soil disturbance relative to straight and convex cutting edges. Increasing rake angle, tine width and operating depth increase degree of soil disturbance and draught requirement. Increasing forward speed reduces residue interference with sowing but might decrease the accuracy and uniformity of depth and separation of seed and fertiliser placement. Relative to common openers, bentleg openers have lower draught and penetration force requirements while combining minimal lateral soil throw with high furrow backfill, even at speeds of up to 16 km h–1. The performance of bentleg openers need to be evaluated under residue conditions and in cohesive and adhesive soils. Recommendations for future research are presented.

Abstract: Diversification of crop species and minimum mechanical soil disturbance are the interlinked principles of conservation agriculture that are beneficial in improving soil physical and hydrological properties, and hence crop productivity. The present study was conducted to assess the long-term impacts of crop rotational diversity and tillage on soil water infiltration (qs), soil water retention (SWR), pore size distribution (PSD), bulk density (ρb) and soil penetration resistance (SPR). The study was established in 1991 at Beresford, South Dakota, and included three crop rotation systems (2-year, maize (Zea mays L.)–soybean (Glycine max L.); 3-year, maize–soybean–wheat (Triticum aestivum L.); and 4-year, maize–soybean–wheat–oat (Avena sativa L.)) and two tillage systems (NT, no-tillage; and CT, conventional tillage). Soil samples were collected only under maize and soybean phases of the crop rotations. Our results showed that NT with 4-year rotation had the lowest ρb under maize and soybean phases (1.21 and 1.19 g cm–3 respectively) compared with the CT system. Similarly, NT with 4-year rotation decreased SPR by 20% compared to CT with 4-year rotation in the soybean phase. Soils managed under NT with 4-year rotation in the soybean phase retained 27, 28, 28, 32, 33, 31 and 26% more water compared with CT and 4-year system at 0–7.5 cm depth at 0, –0.4, –1.0, –2.5, –5.0, –10 and –30 kPa matric potentials respectively. A similar trend was observed for qs under the same treatments, in which it was 31% higher under NT than under CT, both with 4-year rotation. Data from this study showed that diversified crop rotation under NT enhanced soil physical and hydrological properties compared with CT with less diverse systems (e.g. maize–soybean).

Abstract: Portable X-ray fluorescence (pXRF) spectrometry has been successfully used for soil attribute prediction. However, recent studies have shown that accurate predictions may vary according to soil type and environmental conditions, motivating investigations in different biomes. Hence, this work attempted to accurately predict soil pH, sum of bases (SB), cation exchange capacity (CEC) at pH 7.0 and base saturation (BS) using pXRF-obtained data with high variability and robust prediction models in the Brazilian Coastal Plains biome. A total of 285 soil samples were collected to generate prediction models for A (n = 123), B (n = 162) and A+B (n = 285) horizons through stepwise multiple linear regression, support vector machine with linear kernel (SVM) and random forest. Data were divided into calibration (75%) and validation (25%) sets. Accuracy of the predictions was assessed by coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE) and residual prediction deviation (RPD). The A+B horizons dataset had optimal performance, especially for SB predictions using SVM, achieving R2 = 0.82, RMSE = 1.02 cmolc dm–3, MAE = 1.17 cmolc dm–3 and RPD = 2.33. The most important predictor variable was Ca. Predictions using pXRF data were accurate especially for SB. Limitations of the predictions caused by soil classes and environmental conditions should be further investigated in other regions.

Abstract: Process-based models capture our understanding of key processes that interact to determine productivity and environmental outcomes. Combining measurements and modelling together help assess the consequences of these interactions, identify knowledge gaps and improve understanding of these processes. Here, we present a dataset (collected in a two-month fallow period) and list potential issues related to use of the APSIM model in predicting fluxes of soil water, heat, nitrogen (N) and carbon (C). Within the APSIM framework, two soil water modules (SoilWat and SWIM3) were used to predict soil evaporation and soil moisture content. SWIM3 tended to overestimate soil evaporation immediately after rainfall events, and SoilWat provided better predictions of evaporation. Our results highlight the need for testing the modules using data that includes wetting and drying cycles. Two soil temperature modules were also evaluated. Predictions of soil temperature were better for SoilTemp than the default module. APSIM configured with different combinations of soil water and temperature modules predicted nitrate dynamics well, but poorly predicted ammonium-N dynamics. The predicted ammonium-N pool empties several weeks after fertilisation, which was not observed, indicating that the processes of mineralisation and nitrification in APSIM require improvements. The fluxes of soil respiration and nitrous oxide, measured by chamber and micrometeorological methods, were roughly captured by APSIM. Discrepancies between the fluxes measured with chamber and micrometeorological techniques highlight difficulties in obtaining accurate measurements for evaluating performance of APSIM to predict gaseous fluxes. There was uncertainty associated with soil depth, which contributed to surface emissions. Our results showed that APSIM performance in simulating N2O fluxes should be considered in relation to data precision and uncertainty, especially the soil depths included in simulations. Finally, there was a major disconnection between the predicted N loss from denitrification (N2 + N2O) and that measured using the 15N balance technique.

Abstract: No-till has many environmental advantages, but concerns are growing about vehicle-induced topsoil compaction limiting crop growth. We performed a wheeling experiment in a long-term no-till field on an Oxisol with sandy loam texture. The objectives were to measure changes in soil bulk density and corresponding impacts on the least limiting water range (LLWR) due to passage of a maize harvester, and to compare bulk density and LLWR measurements with values simulated using the SoilFlex-LLWR soil compaction model. Soil cores were sampled before and after wheeling, for bulk density measurements and to determine LLWR. Simulated increase in bulk density due to vehicle wheeling agreed well with measurements. However, simulated LLWR and its decrease with compaction were inaccurate. This was ascribed to the pedo-transfer function used in SoilFlex-LLWR to estimate LLWR parameters, which was developed based on data from conventionally tilled sugarcane fields, whereas our site was a long-term no-till soil under a wheat/soybean–maize/black oats rotation. Our measurements showed that LLWR was strongly restricted by soil penetration resistance, which was not captured by the pedo-transfer function incorporated in SoilFlex-LLWR. For better prediction of LLWR, we recommend development of specific pedo-transfer functions or of mechanistic models that can be incorporated in SoilFlex-LLWR.

Abstract: The evaluation of phosphorus (P) transformations in soil after application of manure or mineral P can improve soil management and optimise P use by plants. The objectives of the present study were to assess organic and inorganic P forms in two soils treated with dairy manure and triple superphosphate and to establish relationships between soil P fraction levels and P availability. Soil organic and inorganic P fractions were quantified using a pot experiment with two soils, a typical Hapludox and an arenic Hapludult, with three types of fertiliser treatments applied (no fertiliser application, application of dairy manure, and application of triple superphosphate, by adding 100 mg P dm–3 in the form of fertiliser in the two latter treatments) and four incubation times (15, 45, 90, and 180 days). Inorganic P was fractionated into aluminium-bound, iron-bound, occluded, and calcium-bound P. Organic P was extracted sequentially using sodium bicarbonate, hydrochloric acid, microbial biomass, sodium hydroxide, and residual organic P. After incubation, maize plants were cropped to quantify dry matter yield and absorbed P. Application of dairy manure resulted in a significant increase in most of the organic P fractions, and application of triple superphosphate led to a significant increase in inorganic P fractions. Both fertilisers raised labile organic P fractions in the two soils. The major sinks of P in Hapludox were occluded and fulvic acid-associated P. In contrast, the major sink of P in Hapludult was iron-bound P. The available P levels were stable after application of dairy manure, and decreased with time when fertilised with triple superphosphate. In the Hapludox, the organic P fractions had a significant positive correlation with P uptake by plants. The results suggest that organic P mineralisation plays a more significant role in plant P uptake in the Hapludox soil and inorganic P forms are the main contributors to plant P uptake in the Hapludult soil.

Abstract: Heavy metals accumulate in soil over time and, with changing land use, humans may be exposed to elevated contaminant concentrations. It is therefore important to delineate contaminated sites in the most efficient and accurate manner. Sensors, such as portable X-ray fluorescence (pXRF) and visible near-infrared (vis-NIR) spectroscopy predict metal concentrations more rapidly and in a less hazardous manner compared to traditional laboratory analytical methods. The current study explored the potential for integrating vis-NIR and pXRF outputs to improve lead predictions in fine- (<62.5 µm) and whole-fraction (<2 mm) soil samples. A multi-stage approach was taken to compare different data treatments and combination methods for the prediction of whole-fraction lead content. Data treatment included principal component analysis, and combination methods included concatenation of pXRF and vis-NIR spectra before modelling, and Granger–Ramanathan model averaging of pXRF and vis-NIR model outputs. The most accurate predictions of whole-fraction lead were obtained by Granger–Ramanathan model averaging of vis-NIR Cubist predictions and Compton-normalised pXRF output: Lin’s Concordance Correlation Coefficient (LCCC) = 0.95, root mean square error (RMSE) = 86.4 mg kg–1, Bias < 0.001 mg kg–1 and ratio of performance to inter-quartile range (RPIQ) = 0.37. The most suitable modelling method was then used to predict fine-fraction lead, which provided a similarly accurate model fit (LCCC = 0.94, RMSE = 84.2 mg kg–1, Bias < 0.001 mg kg–1 and RPIQ = 0.34), indicating the potential to reduce the number of samples required for fine-fraction processing. In addition, the quality of the prediction interval estimates was examined – an important aspect in modelling which is underutilised in current literature related to soil spectroscopy.

Abstract: Understanding the mechanism of soil organic carbon (SOC) stabilisation may help in developing management strategies for SOC storage. A long-term organically managed rice−wheat cropping system was used for SOC stabilisation study. Soil samples were collected from control, FYM (farmyard manure to rice and wheat), GM (green manure; Sesbania aculeata to rice and Leucaena leucocephala to wheat), GB (GM with biofertiliser; blue green algae to rice and Azotobacter sp. to wheat), GF (GM with FYM), GFB (GM with FYM and biofertiliser). Sodium hypochlorite (NaOCl)-resistant C correlated significantly with ammonium oxalate and dithionate extractable Fe, Al and Si in soil. The GFB showed the highest enrichment of SOC (32%) as well as NaOCl-resistant C (22%) at 0–15 cm soil depth. At higher soil depth, GM alone showed the highest enrichment of SOC (39% at 15–30 cm, 84% at 30–60 cm). The NaOCl-resistant C was higher in FYM and GFB treatments at 15–30 and 30–60 cm depths respectively. The proportion of NaOCl-resistant C to SOC increased down the profile and was highest (30–52%) in 30–60 cm soil depth. A multiple regression model developed between ammonium oxalate extractable Fe, Al and Si and SOC could well predict the stable SOC content. There was a substantial improvement in prediction when extractable Fe, Al and Si were combined together. Among the organic treatments, GFB showed the highest humification and aromaticity in humic acid with least polarity and more reduced form. The combination of all the organic sources (GFB) could be a promising nutrient management strategy for enhancing the stability of SOC in rice–wheat cropping systems of semiarid subtropical India.

Abstract: Local soil knowledge (LSK) has been recognised for its importance in sustainable soil management and agroecosystems. This paper examines peer-reviewed articles and grey literature documents on LSK during 2003–2018. Research continues to be geographically focused on developing countries, but often in collaboration with researchers from developed countries. There were five key research themes: soil classification and agreement between local and scientific soil knowledge (Theme 1), value of LSK for soil management and decision-making (Theme 2), scientific approach to the incorporation of LSK (Theme 3), application of LSK for identification of and solutions to soil problems (Theme 4) and factors influencing soil knowledge development (Theme 5). Although Theme 1 continued to be a prevalent research area, confirming the importance of visible and topsoil characteristics identified by farmers, examining subsurface soil properties has garnered less research. For LSK to be thoroughly documented requires support by a pluralistic scientific assessment and greater incorporation of social science methodologies. An overarching finding from Themes 2–4 was the importance of designing national programs that incorporate LSK derived from local people and other stakeholders (e.g. scientists and policymakers) to conserve soils. Local soil maps, using LSK terminology, could broaden the appeal and use of maps by local stakeholders to support sustainable land-use planning from the field to national policy-making processes. Finally, cultural and political aspects, known to influence LSK, should be given greater consideration in further research to sustain and develop this knowledge (Theme 5).

Abstract: Partial least-squares regression (PLSR), using spectra from a handheld mid-infrared instrument (the ExoScan), was tested for the prediction of particle size distribution. Soils were sampled from agricultural sites in the Eyre Peninsula under field conditions and with varying degrees of soil preparation. Issues relevant to field sampling were identified, such as sample heterogeneity, micro-aggregate size and moisture content. The PLSR models for particle size distribution were derived with the varying degrees of preparation. Cross-validation of clay content in the as-received in situ soils resulted in low accuracy: coefficient of determination (R2) = 0.55 and root mean square error (RMSE) = 7%. This was improved by manual mixing, drying, sieving to < 2 mm and fine grinding, resulting in R2 values of 0.64, 0.75 and 0.81, and RMSE of 6%, 5% and 4% respectively; less improvement resulted for sand, with corresponding R2 values of 0.82, 0.88, 0.91 and 0.89, and RMSE of 10%, 8%, 6% and 7%. Predictions for silt remained poor. Where only archival benchtop calibration models were available, predictions of clay contents for spectra scanned with the handheld ExoScan spectrometer resulted in high error because of spectral intensity mismatch between benchtop and handheld spectra (R2 = 0.72, RMSE = 24.2% and bias = 21%). Pre-processing the benchtop spectra by piecewise direct standardisation resulted in more successful predictions (R2 = 0.73, RMSE = 6.7% and bias = –1.5%), confirming the advantage of piecewise direct standardisation for prediction from archival spectral libraries.

Abstract: Soil phosphorus (P) reserves, built up over decades of intensive agriculture, may account for most of the crop P uptake, provided adequate supply of other plant nutrients. Whether crops grown on soils with reduced supply of other nutrients obtain similar use-efficiency of soil P reserves remains unclear. In treatments of the Askov Long-Term Experiment (initiated in 1894 on light sandy loam), we quantified changes in soil total P and in plant-available P (Olsen P, water extractable P and P offtake in wheat grains) when P-depleted soil started receiving P in rock phosphate and when P application to soil with moderate P levels ceased during 1997–2017. Additionally we studied treatments with soil kept unfertilised for >100 years and with soil first being P depleted and then exposed to surplus dressings of P, nitrogen (N) and potassium in cattle manure. For soil kept unfertilised for >100 years, average grain P offtake was 6 kg ha–1 and Olsen P averaged 4.6 mg kg–1, representing the lower asymptotic level of plant-available P. Adding igneous rock phosphate to severely P-depleted soil with no N fertilisation had little effect on Olsen P, water extractable P (Pw), grain yields and P offtake. For soils with moderate levels of available P, withholding P application for 20 years reduced contents of Olsen P by 56% (from 16 to 7 mg P kg–1) and of Pw by 63% (from 4.5 to 1.7 mg P kg–1). However, the level of plant-available P was still above that of unfertilised soil. Application of animal manure to P-depleted soil gradually raised soil P availability, grain yield and P offtake, but it took 20 years to restore levels of plant-available P. Our study suggests symmetry between rates of depletion and accumulation of plant-available P in soil.

Abstract: Ash produced during burning of crop biomass may affect the behaviour of herbicides applied in the crops sown after burning. Therefore, the effect of wheat straw ash (WSA) on pretilachlor and rice straw ash (RSA) on sulfosulfuron leaching, degradation and bioactivity in soils was studied. Both ash types reduced downward mobility of respective herbicides, but the effect varied with soil type and dose of ash. Effect was greater in the sandy loam soil because masking of ash was observed in the clay loam soil. Pretilachlor degradation studies indicated that the WSA enhanced degradation and effect was greater in the flooded soil where 0.2% ash reduced the half-life (t1/2) by nearly half, whereas increasing the ash content to 0.5% slightly increased the t1/2 values. The effect of RSA on sulfosulfuron degradation was significant in the sandy loam soil. A pot culture study in wheat also confirmed these results. The effect of the WSA on the bioavailability of sulfosulfuron was assayed by observing its effect on mustard seedlings and results suggested that even 0.1% WSA reduced herbicide availability. Burning of crop residues on field is a major concern due to air pollution, but also affects the fate of soil-applied herbicides. Our study has implications in assaying the role of crop ashes on pesticide fate in soils where crop residues are burned regularly.

Abstract: Repeated puddling for rice cultivation and extensive tillage during wheat cultivation in the north-west of India has adversely affected soil health. Adoption of resource conservation technologies (RCTs) is required for long-term sustainability of conventional rice–wheat systems. However, the behaviour of these technologies is site-specific. A field study was conducted in 2016 to evaluate the medium-term impact of tillage and residue retention on soil physical and biological characteristics. Four treatments were imposed during 2011: conventionally-tilled (CT) rice followed by CT wheat all without residue retention (–M); zero-tilled (ZT) rice followed by ZT wheat and –M; CT rice followed by CT wheat and all with residue retention (+M); and ZT direct-seeded rice followed by ZT wheat and +M. In the surface layer (0–15 cm) of ZT, soil organic carbon (SOC) stock was higher by 15%, mean weight diameter (MWD) by 31.8% and bulk density (BD) by 4% compared to CT averaged across residue treatments. Irrespective of tillage, SOC stock was increased by 19% and MWD by 39% and BD decreased by 1.8% in +M compared with –M in the 0–15 cm soil layer. Infiltration rate was higher in +M than –M irrespective of tillage. Microbial biomass carbon, basal soil respiration and soil enzymatic activities were higher in ZT and +M than CT and –M respectively. Thus, medium-term adoption of RCTs such as ZT and residue retention enhanced soil physical and biological properties in this dry-seeded rice–wheat system. However, whether retaining wheat residue improves soil physical and biological properties requires further investigation.

Abstract: Soil salinisation is a global problem that hinders the sustainable development of ecosystems and agricultural production. Remote and proximal sensing technologies have been used to effectively evaluate soil salinity over large scales, but research on digital camera images is still lacking. In this study, we propose to relate the pixel brightness of soil surface digital images to the soil salinity information. We photographed the surface of 93 soils in the field at different times and weather conditions, and sampled the corresponding soils for laboratory analyses of soil salinity information. Results showed that the pixel digital numbers were related to soil salinity, especially at the intermediate and higher brightness levels. Based on this relationship, we employed random forest (RF) and partial least-squares regression (PLSR) to model soil salt content and ion concentrations, and applied root mean squared error, coefficient of determination and Lin’s concordance correlation coefficient to evaluate the accuracy of models. We found that ions with high concentration were estimated more accurately than ions with low concentrations, and RF models performed overall better than PLSR models. However, the method is only suitable for bare land of coastal soil, and verification is needed for other conditions. In conclusion, a new approach of using digital camera images has good potential to predict and manage soil salinity in the context of precision agriculture with the rapid development of unmanned aerial vehicles.

Abstract: Podzols are soils that display a unique vertical distribution of soil organic matter (SOM). We hypothesise that podzolisation, as a pedogenetic process, influences or even controls content, allocation and quality of SOM. We determined soil organic carbon (SOC) and nitrogen (N) contents in six SOM fractions obtained from mineral horizons of five soils with increasing degree of podzolisation: sand and stable aggregates (S + A), particulate organic matter (POM) > 63 µm and <63 µm, silt and clay (s + c), resistant SOC and dissolved organic matter. We applied infrared spectroscopy to evaluate SOM decomposition state, relative abundance of functional groups and SOM-metal complexation. In topsoil horizons, relative SOC allocation shifted from the larger to the smaller size POM fraction with increasing podzolisation. Accompanied with size reduction, the POM < 63 µm fraction was progressively less decomposed, as derived from infrared spectroscopy and C : N ratios. In illuvial subsoils, the proportion of SOC in the S + A fraction increased with increasing podzolisation, implying SOM accumulation in aggregates and coatings on sand grains. Elevated abundance of carboxylate and aromatic C in the s + c fractions of subsoil horizons indicated their preferred sorption. Additionally, metal-carboxyl complexation increased during podzolisation.

Abstract: Although sowing winter cereal crops in rotation with irrigated cotton (Gossypium hirsutum L.) is practised by many Australian cotton growers, summer cereals such as maize (Zea mays L.) are sown more frequently than previously. Our objective was to quantify the impact of sowing maize rotation crops on soil properties, greenhouse gas emissions, incidence of black root rot (BRR) disease and crop yields in an ongoing long-term experiment located in a Vertosol in north-western New South Wales. The historical treatments were cotton monoculture (sown after either conventional or minimum tillage) and a minimum-tilled cotton–wheat (Triticum aestivum L.) rotation. The experiment was redesigned in 2011 by splitting all plots and sowing either maize during summer following the previous year’s cotton or retaining the historical cropping system as a control. pH and exchangeable cation concentrations were highest, and electrical conductivity (EC1 : 5) lowest during 2012, the season following a flood event, but were unaffected by sowing maize. In subsequent seasons, with the onset of dry conditions, pH and cation concentrations decreased, and EC1 : 5 increased. The upper horizons (0–0.3 m) of plots where maize was sown had higher concentrations of exchangeable Ca and Mg during 2012, and 0.45–1.20 m had higher concentrations of exchangeable Na and exchangeable sodium percentage, but these differences disappeared in subsequent years. Soil organic carbon (SOC) in the surface 0.15 m was higher with maize, with differences becoming evident three years after maize was first sown but without any increases in SOC storage. Soil under maize was less resilient to structural degradation. BRR incidence was lower in maize-sown plots only during 2012. Stepwise linear regression suggested that high concentrations of exchangeable Ca and Mg in the surface 0.15 m played a role in reducing BRR incidence during 2012. Maize rotation introduced into cotton monocultures improved lint yields and reduced greenhouse gas emissions but had little impact in a minimum-tilled cotton–wheat rotation. Maize is a suitable rotation crop for irrigated cotton in a two-crop sequence but is of little advantage in a cotton–wheat–maize sequence.

Abstract: Use of soil cover crops of different families in crop rotation or succession under no-tillage system (NTS) for onion production results in higher soil quality compared to land use systems with less plant diversity. The objective was to evaluate the effect of using different combinations of plant species from different botanical families in rotation and succession of soil cover crops in NTS for onion production on formation of macroaggregates, mesoaggregates, and microaggregates, and on total organic C (TOC) and N (TN) contents, including isotopic forms of C and N, in soil aggregates and bulk soil. The treatments (T) evaluated were maize/onion (NTS-T1); cover plants (winter)/onion (NTS-T2); maize/winter grasses/onion (NTS-T3); velvet bean/onion (NTS-T4); millet/cover plants (winter)/onion (NTS-T5); velvet bean/rye/onion (NTS-T6); maize/onion in conventional tillage system (CTS-T7); and intercrop cover plants (summer)/onion (NTS-T8). We evaluated macroaggregates (8.0–0.25 mm), microaggregates (<0.25 mm), and bulk soil (<2.0 mm) at depths of 0–5, 5–10, and 10–20 cm, in a nine-year field experiment. The greater plant diversity in T2–T6 and T8 resulted in higher geometric mean diameter (GMD) of aggregates compared to T1 and T7. The T8 was more efficient in increasing GMD in the 10–20 cm soil depth than the other treatments. The T1 was more efficient in improving the evaluated soil physical and chemical attributes than T7. The use of NTS with plants of the Poaceae and Fabaceae families in single or intercrop systems for onion production resulted in higher TOC and TN contents in the 0–5 and 5–10 cm soil depths compared to CTS. Isotope 15N measurements showed that C and N were more protected in microaggregates in all evaluated treatments and depths compared to macroaggregates and bulk soil. Macroaggregates had more TOC and TN than microaggregates.

Abstract: Soils are a complex mixture with a variety of mineralogical, chemical, biological and physical properties, which can be explored within forensic case work. This study aimed to apply energy-dispersive X-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectroscopic techniques to discriminate soil samples collected in southern Brazil in a forensic context. Four replicates of soil were collected at four sites: two sites from the same parent material (claystone) and two other sites from limestone and granite/gneiss respectively. The physical and chemical (organic and mineral composition) and spectroscopic techniques (EDXRF and FTIR) produced 16 quantitative variables from only 2 g of sample. The main results from a forensic context were the separation of the soils collected from close neighbourhoods developed on the same parent material and the separation of soils collected in the A and B horizons of the same soil profile. The highest degree of similarity in the clustering of samples collected at the same site was 98.6% (B horizon in claystone domain). In addition to the parent material, the effect of organic matter on the chemical and mineralogical characteristics of the A horizon was important in the grouping dynamics of samples. This work demonstrated the potential of spectroscopic techniques in a forensic context.

Abstract: Maintaining the health, and therefore productivity, of agricultural soils is vital for continued sustainable agricultural production to support the world's growing population. Potatoes are grown in a variety of agro-ecological systems and are one of the most important food crops worldwide. Potato crops are demanding on the soil with significant heavy machinery traffic, intensive tillage operations and high inputs of fertiliser, pesticides and water. Maintaining or improving soil health can therefore be challenging for growers. This review considers the different aspects of soil health in a potato production context, how to measure them and how they can be influenced by management practices. Soil health is a complex concept encompassing the physical, chemical and biological properties of the soil and their role in ecosystem services and the growth of plants. Although our understanding of soil health and its impact on crop productivity has improved in the last 30 years, many knowledge gaps remain.

Abstract: Soil erosion by water affects soil organic carbon (SOC) migration and distribution, which are important processes for defining ecosystem carbon sources and sinks. Little has been done to quantify soil carbon erosion in the three major basins in China, the Yangtze River, Yellow River and Pearl River Basins, which contain the most eroded areas. This research attempts to quantify the lateral movement of SOC based on spatial and temporal patterns of water erosion rates derived from an empirical Unit Stream Power Erosion Deposition Model (USPED) model. The water erosion rates simulated by the USPED model agreed reasonably with observations (R2 = 0.43, P < 0.01). We showed that regional water erosion ranged within 23.3–50 Mg ha–1 year–1 during 1992–2013, inducing the lateral redistribution of SOC caused by erosion in the range of 0.027–0.049 Mg C ha–1 year–1, and that caused by deposition of 0.0079–0.015 Mg C ha–1 year–1, in the three basins. The total eroded SOC was 0.006, 0.002 and 0.001 Pg year–1 in the Yangtze River, Yellow River and Pearl River Basins respectively. The net eroded SOC in the three basins was ~0.0075 Pg C year–1. Overall, the annual average redistributed SOC rate caused by erosion was greater than that caused by deposition, and the SOC loss in the Yangtze River Basin was greatest among the three basins. Our study suggests that considering both processes of erosion and deposition – as well as effects of topography, rainfall, land use types and their interactions – on these processes are important to understand SOC redistribution caused by water erosion.

Abstract: The changes of soil organic matter (SOM) humification induced by long-term combination of tillage and olive mill wastewater (OMW) application compared to natural and cultivated soil have been little investigated. This study aimed to compare effects of no cultivation with natural vegetation soil (NC), tillage (CT1) for 80 years and combination of tillage with OMW application (CT2) for 20 years on SOM humification degree. Fluorescence spectroscopy and UV-visible ratios (E4/E6 and CHA/CFA) were used to study soil humic acids (HAs). The SOM and humification distribution was determined for the whole field area using the Inverse Distance Weighting method. Results showed that SOM content, fluorescence emission area and E4/E6 and CHA/CFA ratios were higher in NC. Tillage reduced SOM amount, molecular size, aromatic condensation and humification degree as shown by the strong correlation between fluorescence area and CHA/CFA ratio in CT1 conversely to E4/E6. Contradictory results between fluorescence emission area and E4/E6 ratio found in NC and CT1 indicated that E4/E6 ratio was not a reliable indicator of SOM humification degree. The SOM amount, CHA/CFA ratio and emission fluorescence area increased conversely to E4/E6 ratio in CT2. This revealed a greatly humified organic matter and aromatic structure condensation with tillage and OMW application. Spatial distribution showed a progressive increase of SOM and CHA/CFA from north-west to south-east linked to the positive relationship between CHA/CFA ratio and SOM amount independent of soil management practices. Soil amended with OMW provided a favourable environment for the development of HAs which improved soil quality. The UV-visible ratio CHA/CFA with fluorescence emission area can be used as parameters to investigate SOM humification degree.

Abstract: The global demand to increase food production from underperforming, water and nutrient limited soils is increasing, which has resulted in an increased dependency on water for irrigation. As fresh water is a finite resource, the increase in irrigation use has resulted in competition between water used for municipal purposes and that used for food and fibre production for an increasing global population. An opportunity exists to improve the efficiency of both urban and agricultural systems by taking green waste compost generated in urban centres and incorporating it into agricultural soils with poor water retention, thereby increasing the ability of these soils to efficiently retain irrigation water for plant use and also to capture a greater volume of water from rainfall. Addition of amendments to soil changes the pore space. The magnitude and cause for this change depends on amendment type, application rate, soil type and climatic conditions. The aim of this research was to determine if the incorporation of municipal compost (MC) can increase the quantity (total volume) and concentration (total volume per unit volume) of soil pores that hold readily available water (defined as macro-mesopores of 30–3 μm diameter) and plant available water (defined as mesopores of 30–0.3 μm diameter). We hypothesised that increases in total porosity would be positively correlated with MC application rate and increases in water holding porosity (macro-mesoporosity and mesoporosity) would be positively correlated with decreasing MC particle size due to the creation of inter-particle pore spaces < 30 μm in diameter. The MC was screened to three different maximum particle sizes – MC4 (<4 mm), MC2 (<2 mm) and MC0.25 (<0.25 mm) – and incorporated into repacked soil cores at five different rates: 0, 5, 25, 50 and 80% wt/wt. Incorporation of MC0.25 increased the concentration and quantity of macro-mesopores and mesopores at significantly lower application rates than MC4 and MC2. The finding that modification of MC particle size can produce targeted changes in inter-particle porosity suggests that this practice has potential to remediate hydraulic limitations of soils.

Abstract: Different fungal isolates closely related to Zopfiella erostrata and Cercophora caudata have been found to colonise plant root tissues in an asymptomatic way in the Monte Desert biome of La Rioja Province, Argentina. This interaction has been newly discovered, and the role of these fungi in their desert habitat has never been studied in detail. The objective of this study was to evaluate eight fungal isolates by means of specific physiological traits that could have implications for their interaction with the host plant. The selected isolates, four endophytic and four rhizospheric, were characterised for their ability to produce indole acetic acid, solubilise and mineralise phosphorus (P), and utilise different nitrogen sources. In addition, we evaluated organic acid production and phosphatase activities as mechanisms of P recycling. These analyses revealed that most isolates produced indole acetic acid, and that all isolates could solubilise and mineralise P, although to different degrees. Furthermore, the production of organic acids correlated with P solubilisation levels, which may enhance P availability in soils. Nitrogen utilisation was variable among the isolates, without specific patterns concerning the different sources and fungal isolates tested. Our results demonstrated that the fungal isolates had great variability, probably because they complete their teleomorphic phase in their habitats, generating viable meiotic spores, in addition to the active dispersion of these fungi by the underground rodent Ctenomys aff. knightii from which they were isolated. Although the isolates were variable, the endophytic isolates exhibited improvement in all the P parameters measured. This can be explained by the ability of these isolates to intimately colonise root tissues, while the colonisation by rhizospheric isolates is produced superficially in the rhizoplane. The high occurrence of this interaction, as well as the physiological traits detected, suggest that this kind of fungi could play an important ecological role in the Monte Desert environment, benefiting the establishment and growth of new seedlings in areas occupied by the rodents.

Abstract: Native grassland supports extensive livestock production in the Pampas of South America, but the impact of cattle excreta on nitrous oxide (N2O) emissions remains unknown in this biome. The objective of this study was to determine the N2O emission factor (EF-N2O, % of N applied that is emitted as N2O) for urine and dung from beef cattle grazing on native grasslands. A field trial was conducted under low and moderate forage allowances (FA4 and FA12; i.e. 4 and 12 kg dry matter/100 kg live weight respectively) during the 30th year of a long-term grassland experiment on a Typic Paleudult in South Brazil. Urine and dung were applied onto separate patches, at rates equivalent to one average urination or defecation; and N2O fluxes were monitored with closed static chambers over 338 days. In adjacent microplots receiving the same excreta treatment, water-filled pore space, nitrate, ammonium and extractable dissolved organic carbon were monitored in the top 0.1 m of soil. Averaged across the forage allowances, daily soil N2O fluxes were low in the control without excreta (1.3 g N ha–1), but increased upon application of dung (3.8 g N ha–1) and urine (66 g N ha–1). The annual N2O emission and the EF-N2O for urine were greater under FA12 than FA4, but no difference was observed for dung. The positive relationships between N2O-N emissions and ammonium intensity and nitrate intensity suggest that N2O may have been produced concurrently by nitrification, nitrifier/denitrification and denitrification. On average, the EF-N2O was almost 10 times higher for urine than for dung (0.74% vs 0.08%), both much lower than the IPCC’s Tier 1 default value of 2%. Our findings reinforce the need for disaggregating the EF-N2O for urine and dung and of revising the IPCC’s Tier 1 EF-N2O.

Abstract: It is important to understand the stability of soil organic matter (SOM) sequestered through land management changes. In this study we assessed differences in carbon (C) stability of pasture soils that had high and low C content (2.35% vs 1.73% whole soil C in the 0–10 cm layer) resulting from long-term phosphorus fertilisation. We used soil size fractionation (fine fraction, coarse fraction and winnowing) to assess the amount of stable C and indicators of microbial decomposition capacity (catabolic profiles, metabolic quotient) to assess C stability. As a main effect throughout the 60-cm profile, C concentrations were higher in the fine fraction soil in the high (excess P fertiliser; P2) than low (no P fertiliser; P0) treatments, demonstrating a larger stable C fraction. For both P2 and P0, there was a strong correlation between C measured in the fine fraction and winnowed fraction in the 0–30 cm layer (R = 0.985, P 0.05). In addition, we conducted two incubation experiments to assess C stability in the treatments with depth and to assess C stability in the physical soil fractions. For the surface soils (0–10 cm), the highest respiration occurred in fractions containing plant material, including roots (coarse fraction, 0.65 g CO2-C kg–1 soil; whole soil, 1.48 g CO2-C kg–1 soil), which shows that the plant material was less stable than the fine and winnowed soil fractions (0.43 and 0.40 g CO2-C kg–1 soil respectively). Soil respiration, microbial metabolic quotient and substrate utilisation were similar in P0 and P2. Collectively, the data show that the increased C in P2 was associated with increased C concentrations in the more stable fine soil fraction, but with no change in the stability of the C within the fractions.

Abstract: Direct-seeded rice (DSR) is a potent option for north-west India considering the current shortages of labour and water. The formation of a subsurface compact layer in medium to coarse textured soils due to continuous puddling used for commonly grown puddled, transplanted rice hampers the root growth of DSR and wheat crops. It is thus imperative to study the deep tillage effects on water balance and water productivity of the DSR–wheat cropping system. A two-year field experiment was conducted during 2016–17 and 2017–18 in a sandy loam soil to study the soil water dynamics in relation to tillage and irrigation regimes in a DSR–wheat cropping system. There were two irrigation regimes both in DSR (irrigation at 4-day and 8-day intervals) and wheat (based on irrigation water to pan evaporation ratio of 1.0 (I1.0) and 0.5 (I0.5)) in main plots; with three tillage treatments in subplots: (1) conventional tillage for both DSR and wheat (DSRCT-WCT), (2) deep tillage before sowing of DSR during the first season + conventional tillage in wheat (DSRDT1-WCT) and (3) deep tillage before sowing of DSR during both seasons + conventional tillage in wheat (DSRDT2-WCT). The irrigation water input was lower by 325 mm under 8-day, I0.5 compared with 4-day, I1.0 irrigation regimes during both years. The evapotranspiration (ET) was significantly higher in plots with the 4-day compared to 8-day irrigation regime by 22.8% and 17.2% during 2016 and 2017 respectively. In wheat, ET was significantly higher in plots with I1.0 than I0.5 by 42.7% and 34.8% during 2016–17 and 2017–18 respectively. The ET was significantly higher in DSRDT2-WCT and DSRDT1-WCT than DSRCT-WCT in DSR. The water productivity was higher in less frequently (8-day and I0.5) than in frequently irrigated (4-day and I1.0) plots. Deep tillage during both seasons (DSRDT2-WCT) had no significant influence on the soil water balance components and water productivity in comparison to deep tillage only once in two years (DSRDT1-WCT). However, the ET and water productivity were significantly higher in plots with deep tillage compared to conventional tillage.

Abstract: Conservation agriculture (CA) is increasingly promoted among smallholder farmers of sub-Saharan Africa in a quest to improve food security while sustaining the natural resource base of the agro-ecosystems where agriculture is based. The aim of this study was to investigate the effects of CA and traditional tillage on soil organic carbon (SOC) and selected hydraulic properties in two contrasting agro-ecological zones of Malawi. Six farmers hosted on-farm trials in each location, with each farmer having the following treatments: CA with continuous sole maize (CA-SM), CA with maize–legume intercrops (CA-ML), and traditional tillage with continuous sole maize (CT-SM). Soil samples were randomly collected in October 2015, from farmers’ fields located in Chipeni, Chinguluwe, Lemu, and Zidyana where CA had been implemented for 10 years (2005–2015) at six depth intervals: 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Bulk density, soil water characteristics, and pore size distribution were determined using undisturbed core samples. At all sites, CA improved total SOC, carbon stocks, and the stable fraction of particulate organic carbon. Maize–legume intercropping under CA had 35%, 33%, and 73% more total SOC than CT-SM in Chipeni, Lemu, and Zidyana respectively. In Chinguluwe and Lemu, CA-ML had 0.54 and 0.50 g kg–1 respectively more stable fraction of particulate organic carbon (POMP) than CT-SM; whereas in Chipeni, CA-SM had 0.73 g kg–1 higher POMP compared with CT-SM. CA also improved soil porosity, pore size distribution, and water retention capacity by increasing the proportion of mesopores and micropores compared with CT-SM. Thus, changing management practices from CT-SM to CA has the potential to improve the soil organic matter and soil hydraulic properties across agro-ecological zones in Malawi, which is important for sustainable agriculture. Farmers should be encouraged to minimise tillage, retain residues as mulch on the soil surface, and practice crop rotation.

Abstract: Forests associating with arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi may have distinct belowground carbon (C) and nitrogen (N) cycle processes. However, there are little available data providing evidence for the effects of trees associating with mycorrhizal type on belowground C and N cycling in forest ecosystems in China. Here, we collected a database of 26 variables related to belowground C and N cycling from 207 studies covering 209 sampling sites in China, to better understand the variations in belowground C and N cycling between the two mycorrhizal types in forest ecosystems along a climatic gradient. The AM forests had significantly lower soil total C and N contents, and soil microbial biomass C and N, than ECM forests, probably due to differences in litter quality (N and C/N) between AM and ECM forest types. In contrast, AM forests had significantly higher litter input, litter decomposition and soil respiration than ECM forests. Temperature and precipitation had significant positive effects on litter input and decomposition, soil total C and N contents, and soil respiration in AM and ECM forests. Overall, our results indicated that mycorrhizal type strongly affected belowground C and N cycle processes in forest ecosystems. Moreover, AM forests are likely more sensitive and ECM forests have a greater ability to adapt to global climate change.