Mineral nitrogen (Nmin = N-NH4 + + N-NO3 −) in oven-dried and field-moist samples was investigated in 2011– 2014 in five areas of Lithuania with soils of different texture (sand, sandy loam, loam and clay) and different mineral nitrogen (Nmin) content. The samples were taken in spring (from late March to early April) and autumn (late October – early November), from the 0–30, 30–60 and 60–90 cm as well as from 0–60 cm soil layers. The aim of the research was to determine the influence of different methods of soil sample preparation on the concentrations of ammonium (N-NH4 +) and nitrate (N-NO3 −) nitrogen in oven-dried and field-moist samples and to assess the suitability of the obtained results for the development of agricultural plant fertilisation plans. According to the research results, drying of soil samples at a temperature of 35°C for 12 hours resulted in significantly higher levels of N-NH4 + compared to those of field-moist samples. The N-NO3 − concentrations in the field-moist samples, when stored at a 4°C temperature for 3 days, increased marginally compared to the oven-dried soil samples. Weak or moderate, however, statistically significant correlations were observed between N-NH4 + concentrations in the oven-dried and field-moist samples. In order to perform faster chemical analyses of soil Nmin for making agricultural plant fertilisation plans, it is necessary to carry out analyses on oven-dried soil samples, and using the linear correlation equations, to convert the results of N-NH4 + analyses into field-moisture data.

http://www.zemdirbyste-agriculture.lt/wp-content/uploads/2018/05/105_2_str13.pdf

Mineral nitrogen in soils of Lithuania’s agricultural land: comparison of oven-dried and field-moist samples

The effect of drying and drying temperature on soil analytical test values

The Nitrogen Soil Test for Rice (N-STaR, Oryza sativa L.) has been calibrated and is being used to predict rice nitrogen (N) fertilizer rates. Research has identified the organic forms of N quantified via N-STaR (NH₄ released by distillation with 10 mol L–¹ NaOH), but no research has looked at the ability of N-STaR to quantify clay-fixed NH₄ (CF-NH₄). This laboratory trial was initiated to determine the amount of CF-NH₄ quantified via N-STaR as well as the influence of soil drying conditions (oven dry vs. field moist) and alkali distillation method (NaOH vs. KOH) on the CF-NH₄ recovered. Seven soils representing five clayey and two loamy soil textures were collected from various rice-producing regions across Arkansas from the 0- to 15-cm and 15- to 30-cm soil depths. Total CF-NH₄ and CF-NH₄ recovered by N-STaR varied greatly across soils and soil depths with a range of 35 to 299 mg N kg soil–¹ and 6 to 21 mg N kg soil–¹, respectively. The N-STaR recovered as much as 15% of total CF-NH₄ and recovery was greatest for silt loam soils. Alkaline hydrolyzable-N (AH-N) concentrations were strongly influenced by soil drying conditions and the alkali used with a higher level (22%) of AH-N recovered from oven-dry than field-moist soils and a higher (7%) recovery of AH-N with NaOH than KOH. These results indicate that the N-STaR method recovers a small, but significant percentage of total CF-NH₄ and may capture the portion of CF-NH₄ that may be plant available during the growing season.

Quantifying Clay-Fixed Ammonium in Paddy Soils and Determining Its Availability Using Alkaline Distillation

Nitrogen dynamics and balance in a lowland rice cropping system.

A greenhouse experiment with sorghum sudangrass (Sorghum bicolor × Sorghum sudanense) and maize (Zea mays) was conducted to assess information on differences in their nitrogen and fertilizer utilization when used as energy crops. The aim was to contribute to the scarce data on sorghum sudangrass as an energy crop with regards to nitrogen derived from fertilizer (NdfF) in the plant’s biomass and fertilizer nitrogen utilization (FNU). Sorghum sudangrass and maize were each grown in eight bags of 45 L volume and harvested at maturity after 154 days. Each crop treatment was further divided in a control treatment (four bags each) that did not receive N fertilization and a fertilization treatment (four bags each) that received 1.76 g N, applying a 15N-labelled liquid ammonium nitrate fertilizer. Fertilization took place at the start of the experiment. After harvest, the whole plant was divided in the fractions “aboveground biomass” (ABM) and “stubble + rootstock” (S + R). Weight, N content and 15N content were recorded for each fraction. In addition, N content and 15N content were assessed in the soil before sowing and after harvest. The experiment showed that FNU of sorghum sudangrass (65%) was significantly higher than that of maize (49%). Both crops accumulated more soil N than fertilizer N. The share of fertilizer N on total N uptake was also higher with sorghum sudangrass (NdfF = 38%) compared to maize (NdfF = 34%). The observations made with our control plant (maize), showed that the results are plausible and comparable to other 15N studies on maize regarding yields, NdfF, and FNU, leading to the assumption that results on sorghum sudangrass are plausible as well. We therefore conclude that the results of our study can be used for the preliminary parametrization of sorghum sudangrass in soil organic matter (SOM) balance at field level. 

Uptake of Fertilizer Nitrogen and Soil Nitrogen by Sorghum Sudangrass (Sorghum bicolor × Sorghum sudanense) in a Greenhouse Experiment with 15N-Labelled Ammonium Nitrate

In order to monitor spatial inorganic N concentrations in soils over time, collected soil samples are composited and thoroughly mixed. The sticky characteristic of Vertisol when wet makes it difficult to thoroughly mix wet samples. There is the need for appropriate drying of Vertisol samples to facilitate thorough mixing and storage to retain mineral N content reflective of field status. We determined the effects of drying method, storage period and C:N ratio on inorganic N contents of tropical Vertisols. The treatments comprised of three soils with different C:N ratios, five drying methods inclusive of a check (method 1), and five storage periods including a check (period 1). Storage temperature was -10°C. In method 1, field-fresh soil samples were kept at -10°C and later used for mineral N extraction using 0.5 M K2SO4. Period 1 involved storing soil samples for two days from sampling date before mineral N extraction. Ammonium-N and NO3 -N were determined using colorimetric method. Method 1 x period 1, for each soil, resulted in NH4+-N and NO3--N contents significantly different from other treatments indicating that extraction for mineral N should be done on field moist soil not later than two days after sampling. Key words : Drying method, mineral nitrogen, storage period, soil preparation, Vertisols.

/pdf/effects-of-drying-method-storage-period-and-carbon-nitrogen-90n0m02sqq.pdf

Effects of drying method, storage period and carbon: nitrogen ratio on inorganic nitrogen contents of Vertisols

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Effects of drying method, storage period and carbon: nitrogen ratio on inorganic nitrogen contents of Vertisols