D.R. Linden

Soil organic carbon and 13C abundance as related to tillage, crop residue, and nitrogen fertilization under continuous corn management in Minnesota

Long-term field experiments are among the best means to predict soil management impacts on soil carbon storage. Soil organic carbon (SOC) and natural abundance 13 C( d 13 C) were sensitive to tillage, stover harvest, and nitrogen (N) management during 13 years of continuous corn (Zea mays L.), grown on a Haplic Chernozem soil in Minnesota. Contents of SOC in the 0‐15 cm layer in the annually-tilled [moldboard (MB) and chisel (CH)] plots decreased slightly with years of corn after a low input mixture of alfalfa (Medicago sativum L.) and oat (Avena sativa L.) for pasture; stover harvest had no effect. Storage of SOC in no-till (NT) plots with stover harvested remained nearly unchanged at 55 Mg ha ˇ1 with time, while that with stover returned increased about 14%. The measured d 13 C increased steadily with years of corn cropping in all treatments; the NT with stover return had the highest increase. The N fertilization effects on SOC and d 13 C were most evident when stover was returned to NT plots. In the 15‐30 cm depth, SOC storage decreased and d 13 C values increased with years of corn cropping under NT, especially when stover was harvested. There was no consistent temporal trend in SOC storage and d 13 C values in the 15‐30 cm depth when plots received annual MB or CH tillage. The amount of available corn residue that was retained in SOC storage was influenced by all three management factors. Corn-derived SOC in the 0‐15 cm and the 15‐30 cm layers of the NT system combined was largest with 200 kg N ha ˇ1 and no stover harvest. The MB and CH tillage systems did not influence soil storage of corn-derived SOC in either the 0‐15 or 15‐30 cm layers. The corn-derived SOC as a fraction of SOC after 13 years fell into three ranges: 0.05 for the NT with stover harvested, 0.15 for the NT with no stover harvest, and 0.09‐0.10 for treatments with annual tillage; N rate had no effect on this fraction. Corn-derived SOC expressed as a fraction of C returned was positively biased when C returned in the roots was estimated from recovery of root biomass. The half-life for decomposition of the original or relic SOC was longer when stover was returned, shortened when stover was harvested and N applied, and sharply lengthened when stover was not harvested and N was partially mixed with the stover. Separating SOC storage into relic and current crop sources has significantly improved our understanding of the main and interacting effects of tillage, crop residue, and N fertilization for managing SOC accumulation in soil. Published by Elsevier Science B.V.

Long-term corn grain and stover yields as a function of tillage and residue removal in east central Minnesota

Because the adoption of conservation tillage requires long-term evaluation, the effect of tillage and residue management on corn (Zea mays L.) grain and stover yields was studied for 13 seasons in east central Minnesota. Three primary tillage methods (no-till (NT), fall chisel plow (CH), fall moldboard plow (MB)) and two residue management schemes (residue removal versus residue returned) were combined in a factorial design experiment on a Haplic Chernozem silt loam soil in Minnesota. No significant effects on grain yield were seen due to tillage treatments in 9 out of 13 years. The NT treatment resulted in lower yields than CH and MB treatments in years 6 and 7, and lower than the MB in year 8, indicating a gradual decrease in yield over time with continuous use of NT. There were differences due to residue management in 8 out of 13 years. The residuereturned treatments contributed about 1 Mg ha ˇ1 greater yields in intermediate level dry years such as years 3 and 6, which had cumulative growing season precipitation 20 and 30% below the 9-year average, respectively. In excessively dry or longterm-average years, residues resulted in little yield difference between treatments. The most pronounced effects of residues were with the CH treatment for which yields were greater in 8 out of 13 years. The ratio of grain to total dry matter yield averaged 0.56 and did not vary with time or between treatments. These results apply primarily to soils wherein the total water storage capacity and accumulated rainfall are insufficient to supply optimum available water to the crop throughout the growing season. Under conditions with deeper soils or in either wetter or drier climates, the results may differ considerably. Published by Elsevier Science B.V.

Modeling the incorporation of corn (Zea mays L.) carbon from roots and rhizodeposition into soil organic matter

Experimental data reported in the literature over the last decennium indicate that roots and rhizodeposition are important sources of carbon for the synthesis of soil organic carbon. Our objective was to verify the capability of the simulation model NCSWAP to reproduce the general conclusions from the experimental literature, and to gain some insight about the processes that control the incorporation of corn belowground production into the soil organic matter. The model was calibrated against the experimental data gathered from a long-term field experiment located near St. Paul, Minnesota. The simulation model updated daily the soil conditions to reproduce over a 13 year period the measured kinetics of seven variables: above-ground corn production, and the total soil organic matter, soil d value, and the soil organic matter derived from corn in the 0‐15 and 15‐30 cm depth. The simulation gave a root-plus-rhizodeposition 1.8 times larger than stalks plus leaves. The translocation efficiency of corn-C into soil organic C at the 0‐15 cm depth gradually decreased to 0.19 of the below-ground deposition. The sensitivity of below-ground photosynthate incorporation into the soil organic matter was analyzed relative to variations in the parameters that control the formation and decay of roots and rhizodeposition. Roots had a greater effect than rhizodeposition on the soil organic matter, though more photosynthates were translocated to rhizodeposition than to roots. q 2001 Elsevier Science Ltd. All rights reserved.

Nitrogen-tillage-residue management. I. Simulating soil and plant behavior by the model NCSWAP

SummaryNCSWAP (nitrogen and carbon cycling in soil, water and plant) is a simulation model of the soil-crop-water system which integrates water flow dynamics, crop growth, N transformations, tillage and residue effects, soil temperature, and solute transport. A small plot field study was initiated in May of 1980 to determine the effects of N rate (2 or 20 g N/m2), tillage (rototill or no-till), and residue management system (residue return or noresidue) on soil parameters, and maize (Zea mays L.) production.Significant differences due to treatments (N rate, tillage, and residue) were not detected in 1981 for the measured soil-plant parameters including soil moisture, yield, and N uptake. Therefore, two representative treatment combinations (N rates of 2 or 20 g N/m2-tilled-no residue) characterized the field research data. Calculated and observed data sets were compared for several parameters including: (1) soluble NO3−N, (2) N leaching losses (3) plant total-N and15N, (4) root growth, (5) soil moisture, and (6) fertilizer efficiency.The objectives of this study were to initiate the validation process of the model NCSWAP, and to illustrate how NCSWAP can be used as a research tool to infer operational characteristics of the N cycle.

Simulation of Nitrogen, Tillage, and Residue Management Effects on Soil Fertility

A comprehensive simulation model of the soil-crop-water system has been developed as a management tool for nitrogen, tillage, and crop residues. The overall model integrates process level submodels for water flow, crop growth (including roots), nitrogen transformations, tillage effects, soil temperature, soil chemistry, and solute transport to provide an Interactive process simulation. The nitrogen-tillage-residue management model is capable of seasonal and longer-term estimates of soil fertility and its effects on crop yield. Model validation and verification have been obtained for each submodel and for the overall model package. Output from the model can be used in farm and extension level management programs and models, in research and engineering studies, and in teaching programs. The NTRM1 model has been made “user friendly” by developing an extensive user operating system, computer graphics capabilities, and user documentation. The model can be directly accessed via remote terminals through Telenet or similar telephone systems, and the ANSI standard FORTRAN source code is available for adaptation to a specific computer.

Tillage influence on redox potentials following rainfall

Tillage influences many soil properties which impact the oxygen flux into the soil profile. Rainfall can amplify the influence of tillage on relative aeration by differentially saturating the soil profile with water, and thus reducing oxygen flux into the soil. Understanding how tillage influences relative aeration following rainfall is important in order to evaluate the effect of soil physical properties on biological activity and the decomposition of organic compounds. The objective of this study was to investigate the influence of rainfall on redox potential patterns for different tillage and residue management treatment combinations. Platinum electrodes, copper-constantan thermocouples, and tensiometers were installed in soil that had been under rototill/residue-incorporated or no-till/surface-residue treatments after 6 years of a continuing field experiment at depths of 7, 15, and 22 cm during a complete corn (Zea mays L.) growing season. Climatic and physical factors interacted to determined the impact of tillage on the redox potentials following rainfall.

Nitrates in Soils and Waters from Sewage Wastes on Land

Research was initiated in 1973 at St. Paul, Minnesota, with objectives to develop efficient, practical, and environmentally safe methods for utilizing sewage wastes on land in harmony with agricultural usage. Applications of municipal sewage sludge and/or wastewater effluent were studied. Liquid digested sewage sludges from several wastewater treatment plants were applied to a 16-ha terraced watershed cropped to maize ( Zea mays L.) and reed canarygrass ( Phalaris arundinacea L.). The sludge was transported to the site by tank truck, stored in lagoons, and spread by combinations of traveling gun and subsurface injection. Sludge was applied to the maize areas for 20 years (total of 68 cm, 224 tonnes ha −1 solids, and 9460 kg ha −1 total N) and to the reed canarygrass areas for 12 years (total of 96 cm, 173 tonnes ha −1 solids, and 10 040 kg ha −1 total N). Crop yields were high with normal plant tissue concentrations of N, P, and K. Analysis of water samples from runoff, soil, and ground water showed no movement of potentially polluting materials out of the watershed via surface runoff or leaching. Wastewater effluent was sprinkled onto a 2-ha area containing maize and eight forage species for a four-year period at about 5 and 10 cm wk −1 (total of 120 to 280 cm yr −1 and 260 to 680 kg N ha −1 yr −1 ). Tile drainage, ground and soil water, soils, and crops were analyzed for N, P, K, and trace metals. Maize and forage grasses produced high yields (average of 13.4 and 11.1 tonnes ha −1 for maize and reed canarygrass, respectively). Removal of N and P from effluent by the combination of crop uptake and soil sorption was satisfactory. No increase in trace metal concentrations was detected in either the water percolate or crops. Special management of the crop was important for maintaining adequate infiltration rates, for producing high yields of dry matter, and for maximum removal of N.