Organic Carbon, Nitrogen, and Phosphorus Concentrations and pH in Soil Profiles as Affected by Tillage Intensity

TL;DR: Dick et al. as mentioned in this paper investigated the effect of various tillage intensities on the profile (0-30 cm) distribution of organic C, N, and P concentrations and pH was investigated.

Abstract: No-tillage (NT), minimum tillage (MT), and conventional tillage (CT) practices were continuously applied to a Hoy tville silty clay loam (Mollic Ochraqualf) soil (18 years) and a Wooster silt loam (Typic Fragiudalf) soil (19 years) in Ohio. The effect of the various tillage intensities on the profile (0-30 cm) distribution of organic C, N, and P concentrations and pH was investigated. Results showed that NT resulted in significantly (P < 0.05) higher organic C and N concentrations in the 0to 15-cm soil increment of the Hoy tville soil but significantly lower concentrations in the 15to 30-cm soil increment. For the Wooster soil, NT resulted in higher concentrations in the 0to 7.5-cm soil increment. No significant differences were observed among tillage intensities in the 7.5to 30-cm soil increment. Comparison of organic C concentrations in the plow layer (0-22.5 cm) of the soils at the beginning of the longterm tillage experiment and at present showed that concentrations remained constant or decreased 11 % under NT in the Hoytville and Wooster soils, respectively. Present organic C concentrations in the Hoytville 1 Contribution from the Dep. of Agronomy, Ohio Agric. Res. & Dev. Ctr., Wooster, OH 44691. Published with approval of the Director as Paper no. 72-82. Received 19 May 1982. Approved 24 Aug. 1982. * Assistant Professor, Dep. of Agronomy, The Ohio State University and The Ohio Agric. Res. & Dev. Ctr., Wooster, OH 44691. soil were decreased 12 to 14% by long term MT or CT while a 23 to 25% decrease was observed for the Wooster soil. Organic P concentrations under NT were significantly (P < 0.05) higher in the 0to 7.5cm increment of the Wooster soil and significantly lower in the 22.5to 30-cm soil increment. Organic C/N, C/P, and N/P ratios were calculated and higher ratios were observed under NT than under MT or CT in the surface soil increments. Tillage intensity, however, had little effect on the ratios averaged over the entire profile (0-30 cm). Soil pH was 0.1 to 0.3 units lower (P < 0.05) under NT in all soil increments except in the 22.5to 30-cm increment of the Wooster soil where no significant differences in pH were observed among the tillage intensities. Additional Index Words: no-till, zero tillage, minimum tillage, nutrient distribution, organic C/N/P ratios. Dick, W.A. 1983. Organic carbon, nitrogen, and phosphorus concentrations and pH in soil profiles as affected by tillage intensity. Soil Sci. Soc. Am. J. 47:102-107. A INCREASING NUMBER of farmers are changing to crop production methods which are less tillage-intensive. No-tillage, defined as a crop production system DICK: ORGANIC C, N, AND P CONCENTRATIONS AND PH IN SOIL PROFILES AFFECTED BY TILLAGE INTENSITY 103 where weed control is accomplished entirely by herbicides and tillage is limited to the opening of a small slot for seed placement, is a method rapidly being adopted by farmers throughout the U.S. This is because no-tillage reduces soil erosion and fuel use, conserves soil water, and allows row-crop production to be practiced on steeply sloping farmland. By the year 2000 an estimated 65% of the seven major crops (corn, soybeans, sorghum, wheat, oats, barley, and rye) in the U.S. will be grown by the no-tillage system and 78% by the year 2010 (Phillips et al., 1980). With no-tillage, mechanical incorporation of fertilizer within the soil plow layer is not possible and the nutrients taken up by plant roots from the subsoil and incorporated into the plant are subsequently deposited on the soil surface as plant residue. A few reports on changes in the distribution of organic matter, nutrients, and acidity (pH) in the soil profile as a result of no-tillage practices have been previously published (Van Doren et al., 1976; Blevins et al., 1977; Juo and Lal, 1979; Doran, 1980). These reports, however, dealt with studies on sites where continuous no-tillage crop production practices had been maintained for only 10 years or less and cannot describe longer-term effects of continuous no-tillage. In Ohio, experiments dealing with various tillage intensities (no-tillage, minimum tillage, and conventional tillage) were begun in 1962 and 1963 and have continued to the present. These 18and 19-year continuous tillage experiments have allowed a much greater time for changes in organic matter, nutrients, and pH to become established. The objectives of this study were to investigate changes in organic C, N, and P concentrations and pH as affected by tillage intensity in soil profiles collected from these long-term experimental plots. MATERIALS AND METHODS Experimentation on a Hoytville silty clay loam (fine, illitic, mesic Mollic Ochraqualf) soil and a Wooster silt loam (fine, mixed, mesic Typic Fragiudalf) soil concerning the effects of tillage intensity on crop production was begun in 1963 and 1962, respectively. This corresponds to an 18-year period where the various tillage intensities have been continuously applied at the Hoytville site and a 19-year period at the Wooster site. The complete history and the soil characteristics of these sites were described by Van Doren et al. (1976). Briefly, prior to the beginning of the tillage experiment, the Hoytville site (slope, < 1%) had been maintained for 6 years in a conventional tillage corn-oats-meadow rotation and a grass meadow had been maintained for 6 years at the Wooster site (slope, 2.5 to 4.0%). Soil characteristics observed at the two sites can be attributed primarily to parent material, topography, drainage, and shrinkswell potential. The Hoytville soil has poor surface and internal drainage when wet but cracks substantially when dry. In contrast, the Wooster soil has much better surface and internal drainage and little or no shrink-swell potential. At each site nine combinations of three levels of each of two variables in a complete factorial, randomized block design with three replications were established. The tillage variable is defined as follows: 1. No-tillage (NT)—planting was accomplished directly into the proceeding years crop residue by means of a coultertype planter. 2. Minimum tillage (MT)—moldboard plow 20 to 25 cm deep with no other tillage prior to planting. 3. Conventional tillage (CT)—moldboard plow 20 to 25 cm deep and at least two other 10-cm deep secondary tillage operations prior to planting. The rotation variable consisted of (i) continuous corn, (ii) corn and soybeans, and (iii) corn, oats, and alfalfa meadow in a 3-year rotation. Sufficient numbers of plots were established so that each crop in each of the nine treatments appeared each year. The same tillage treatments have been maintained on each plot to the present time. Tilled treatment plots were plowed in the spring 1 to 4 weeks before planting for the Wooster soil and in the fall for the Hoytville soil. The third year (meadow) of the corn-oatsmeadow rotation received no tillage prior to planting. Common management practices were maintained for the various rotations across the tillage treatments, i.e., the total amount of N, P, K, and lime applied was the same for the three tillage treatments and in all cases was broadcast-applied. Fertilizer was broadcast in the spring prior to planting and lime was broadcast in the winter as required to maintain a pH in the Ap horizon of the continuous corn plots at or above 6.0. Herbicide materials and rates varied with years but the total amounts added to the NT plots compared to the MT or CT plots was approximately one-third greater over the experimental time period. Soil samples (2.5-cm outer diameter soil cores) from 0 to 1.25 cm, 1.25 to 2.5 cm, 2.5 to 7.5 cm at 2.5-cm increments, and from 7.5 to 30 cm at 7.5-cm increments from the NT plots and from 0 to 30 cm at 7.5-cm increments from the MT and CT plots were collected prior to tillage in the fall of 1980. Samples were obtained after first removing from the soil surface easily identified plant materials, i.e., corn stalks and leaves. The soils were air-dried and ground to pass through a 60-mesh sieve. Soil pH was determined by a glass electrode (soil-to-water ratio, 1:1), organic C by the Walkley-Black method (Allison, 1965), organic N was determined by semimicro-Kjeldahl digestion as described by Bremner (1965), and organic P was obtained by subtracting the value of inorganic P (Olsen and Dean, 1965) from the value obtained for total P (Dick and Tabatabai, 1977). All concentrations reported for organic C, N, and P are expressed on a gravimetric basis. For the statistical analyses, the concentration of the various parameters measured in the 0to 7.5-cm soil increment for the NT plots was obtained by calculating a weighted average of the concentrations in the 0to 1.25-, 1.25to 2.5-, 2.5to 5.0-, and 5.0to 7.5-cm soil increments. Data were interpreted using analysis of variance and Duncan's Multiple Range Test. RESULTS AND DISCUSSION The main effect of tillage intensity on organic C, N, and P concentrations and on pH in soil profile samples will be the focus of this paper. No mention of rotation effects and interaction effects of tillage and rotation will be made. Data for all three tillage treatments will be presented but in most cases the results for the MT and CT treatments were similar.