Progress 10/01/01 to 09/30/06
Outputs
One of the most widely referenced theories in soil fertility research is Liebig's, Law of the Minimum. This theory states that plant growth is limited by the plant nutrient that is in the smallest quantity, with all others being present in adequate amounts. Liebig's, Law of the Minimum, does not account for synergistic relationships between yield limiting factors, and therefore it may not be appropriate for site specific applications. The objective of this research was to investigate the effect of N on water use efficiency and water on nitrogen use efficiency in corn (Zea mays L.). A randomized block experiment was conducted in 2002, 2003, and 2004. Blocks were split into natural and natural + supplemental irrigation treatments. Four rates of urea fertilizer (0, 56, 112, and 168 kg N ha-1) were applied to irrigation treatments. The efficiency of precipitation, soil N, and fertilizer N were determined. The utilization of grain N derived from the soil was determined
using the natural abundance δ15N approach. Findings from this study showed that: 1) plants responded to N and water simultaneously; 2) N fertilizer increased precipitation use efficiency and water increased soil and N use efficiency; and 3) the net effect of a synergistic relationship between N and water was that the amount of N fertilizer per kg of grain was less in the irrigated than the non-irrigated treatment. Findings from this study suggest that N recommendation models based on Liebigs, Law of the Minimum, are not appropriate for precision farming purposes and to improve site-specific N recommendations interactions among multiple factors must be considered.
Impacts
improved N fertilizer recommendations
Publications
- Chang, J., and D.E. Clay. 2006. Identifying factors for yield prediction models and evaluating model selection methods. Korean Crop Sci. Soc. J. Korean J Crop Science 50:268-275.
- Clay, D.E., Ki-In Kim, J. Chang, S.A. Clay, and K. Dalsted. 2006. Characterizing water and N stress in corn using remote sensing. Agron. Journal. 98:579-587.
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Progress 01/01/05 to 12/31/05
Outputs
Techniques for measuring soil organic C (SOC) turnover in production fields are needed. The objectives of this study were to propose and test non-isotopic and 13C stable isotopic techniques for assessing SOC turnover. Based on SOC equilibrium and mass balance relationships an equation, NHC/SOCinitial= [1/(SOC*kNHC )] (dSOC/dt) + kSOC/kNHC , where dSOC/dt was the annual change in SOC, NHC was non-harvested C returned to soil, kSOC was the annual mineralization rate of SOC, and kNHC was the annual mineralization rate of NHC was derived. Maintenance rate were calculated by: (i) defining NHC/SOCinitial as y and (dSOC/dt) as x; (ii) fitting the data to a zero order rate equation; and (iii) multiplying SOC times the y intercept. An isotopic approach that was based on simultaneously solving the equations was developed. Using this approach C budgets could be delopeved. Both approaches were tested on a production field where above ground corn (Zea mays) and soybean (Glycine
max) yields were measured with a yield monitor and soil samples collected from a slightly offset grid (30 m) in 1995 and 2003 were analyzed for organic C and 13C discrimination. Analysis of the non-isotopic approach showed that maintenance rates increased with SOC and that an accurate measure of NHC was required to calculate maintenance requirements. Sensitivity analysis of the isotopic approach showed that calculated budgets were sensitive to 13C discrimination. If 13C discrimination during SOC and NHC mineralization did not occur, then 14.9 and 7.6 % of the SOC measure in 1995 (SOCinitial) were mineralized, and 7,420 and 2,780 kg C ha-1 of NHC was incorporated into SOCfinal, in the 523.4- 527.3 and 527.3-529.2 m elevation zones, respectively. Landscape differences were attributed to drainage stimulating C mineralization.
Impacts
Results from this research showed that organic C at different elevation zones has different stabilities. Organic matter in summit/shoulder areas was much more stable than organic matter in footslope areas. Landscape differences has implications toward N management.
Publications
- Clay, D.E., C.G. Carlson, S.A. Clay, J. Chang, and D.D. Malo. 2005. Soil organic C maintenance in a corn (Zea mays L.) and soybean (Glycine max L.) as influenced by elevation zone. Journal of Soil Water and Conservation. 60:342-348.
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Progress 01/01/04 to 12/31/04
Outputs
A critical component in developing crop management systems that mitigate economic, environmental, and energy related problems is the ability to measure and predict the impacts of management on soil organic carbon (SOC). The objectives of this study were to propose and develop C-budgets for fields containing spatial variability. The approach is based on 13C isotopic discrimination changes over time. SOC retained in soil was calculated with the equation, SOC retained = [SOC final (13C discrimination(soil final) - 13C discrimination (plant C added))/(13C discrimination (soil initial) - 13C discrimination (plant C added)). The amount of C incorporated into the soil was the difference between SOC final and SOC retained. The average amount of annual C additions required to maintain SOC was calculated using the equation, NHC/SOCinitial= m (dSOC/dt) +b, where NHC was the average amount of nonharvested C returned to soil. When dSOC/dt was zero, b times the SOC initial was the
average annual C additions required to maintain surface soil SOC. Soil samples (0-15 cm) collected from a 30 by 30-m grid in May of 2005 and May/June of 2003 were analyzed for SOC and 13C discrimination. SOC and 13C discrimination values were aggregated to grid-cells from which elevation-based C budgets were developed for a 65-ha field cropped to corn and soybean. SOC and 13C discrimination contained substantial spatial variability. The isotopic approach determined that 14.6 and 9.0 % of the SOC measure in 1995 in elevation zones less than 527.3 m and greater than 527.3 m, respectively were mineralized, and that 7,560 and 3,630 kg C/ha of new C was incorporated into surface soil SOC in elevation zones less than 527.3 m and greater than 527.3 m, respectively. Differences between C inputs and mineralization suggest that a small amount of C was lost from the soil(630 kg C/ha)during the 8 years of the study. The isotopic and non-isotopic approaches were consistent and complemented each
other. Elevation zone differences in C-budgets were attributed to landscape processes that impacted water stress and root and shoot growth characteristics and tile-line repairs that increased SOC susceptibility in footslope areas to mineralization.
Impacts
By understanding soil organic mineralization kinetics, we will be better able to manage water and N fertilizer inputs.
Publications
- Clay, D.E., C.G. Carlson, and J. Chang. 2004. Identifying the Best Approach to Identify Nutrient Management Zones: A South Dakota Example SSMG 41. Clay et al. (Ed) Site Specific Management Guidelines. Potash and Phosphate Institute. Norcross, GA.
- Chang, J. D. E. Clay, C. G. Carlson, C. L. Reese, S. A. Clay, and M.M. Ellsbury. 2004. The Influence of different approaches to define yield goals and management zones on N and P fertilizer recommendations errors. Agron. J. 96:825-831.
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Progress 01/01/03 to 12/31/03
Outputs
Field experiments that evaluate N mineralization and nitrate leaching often assume that Br, 14N-nitrate and 15N-nitrate have similar leaching kinetics. This study tested this assumption. Twenty-four undisturbed soil columns (15-cm diameter) were collected from summit/shoulder, backslope, and footslope positions of a no-tillage field with a corn (Zea mays) followed by soybean (Glycine max) rotation. Each of the landscape positions had a different soil series. After conditioning the columns with 4 L of 0.01 M CaCl2 (2 pore volumes), 15N labeled Ca(NO3)2 and KBr were applied to the soil surface, and they were leached with 4 L of 0.01 M CaCl2. Leachate was collected, weighed, and analyzed for nitrate, ammonium, 15N, 14N, and Br. The total amount of 15N-nitrate and 14N-nitrate collected in 1000, 2000, and 3000 mL of leachate were similar. These data suggests that 15N discrimination during leaching did not occur. Bromide leached faster through the columns than nitrate--N.
The more rapid transport of Br than nitrate was attributed to lower Br (0.002 mg kg) than nitrate(0.17 mg kg) sorption. Results from this study suggest that: (i) if Br is used to estimate nitrate leaching loss, then nitrate leaching losses may be overestimated by 25%; (ii) the potential exists for landscape position to influence anion retention and movement in soil, and (iii) 15N discrimination was not detected during the leaching process.
Impacts
By understanding the leaching kinetics of different tracers, we will be better able to predict N mineralization and the amount of nitrate lost through leaching.
Publications
- Clay, D.E., Z. Zhen, Z. Liu, S.A. Clay, and T.P. Trooien. 2004. Bromide and nitrate leaching in undisturbed soil columns collected from three landscape positions. J. Environ. Qual. 33:338-342
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Progress 01/01/02 to 12/31/02
Outputs
The objective of this study was to determine the impact of different techniques of identifying management zones on soil NO3-N and Olsen-P sampling variability. Approaches evaluated for locating N and P management zone sampling boundaries included: (i) sampling areas impacted by old homesteads or grazing separately from the rest of the field; (ii) sampling different blocks; (iii) using geographic information systems (GIS) or cluster analysis to identify zones based on apparent electrical conductivity, elevation, aspect, and distance (connectedness) information; and (iv) sampling each soil series separately. Soil samples collected on a 60 by 60 m or smaller grid, in three fields that were 65, 53, and 40 ha, were analyzed for NO3-N and Olsen-P. F values were used to determine if the sampling approach reduced nutrient sampling variability. The F statistics were calculated by dividing the variances for the entire data set by the pooled variances for each sampling approach.
Relative to whole field sampling, the 4-ha block sampling combined with sampling old homesteads separately from the rest of the field reduced the percentage of the field that was under-fertilized for P and N 36 and 35%, respectively. Improving fertilizer recommendations should improve profitability. Results from this study suggested that: (i) old homesteads and grazing areas should be sampled separately from the rest of the field; and (ii) soil sampling variation can be reduced by block sampling. Locating zone boundaries using either GIS or cluster analysis of EC, elevation, and aspect information did not consistently reduce sampling variability.
Impacts
By developing techniques to identify nutrient management zones, preliminary research suggests that N and P fertilizer recommendations can be improved.
Publications
- Clay, D.E., S.A. Clay, J. Jackson, K. Dalsted, C. Reese, Z. Liu, D.D. Malo, and C.G. Carlson. 2003. C13 discrimination can be used to evaluate soybean yield variability. Agron. J. (in press).
- K.A. Sudduth, N.R. Kitchen, W.D. Batchelor, G.A. Bollero, D.G. Bullock, D.E. Clay, H.L. Palm, F.J. Pierce, R.T. Schuler, K. Thelen, and W.J. Wiebold. 2002. In Robert et al (eds.). Characterizing field-scale soil variability across the Midwest with electrical conductivity. Proceedings of the 6th International Conference of Precision Agriculture July 14-17 2002, Minneapolis MN. (in press).
- Drummond, S.T., K.A. Sudduth, N.R. Kitchen, W.D. Batchelor, G.A. Bollero, D.G. Bullock, D.E. Clay, H.L. Palm, F.J. Pierce, R.T. Schuler, K. Thelen, and W.J. Wiebold. 2002. In Robert et al (eds.). Neural network analysis of site-specific soil, landscape and yield data. p. 59. Proceedings of the 6th International Conference of Precision Agriculture July 14-17 2002, Minneapolis MN. (in press).
- Chang, J., D.E. Clay, C.G. Carlson, S.A. Clay, and D.D. Malo. 2002. The influence of different classification approaches on N an P fertilizer recommendations. Proceedings of the 6th International Conference of Precision Agriculture July 14-17 2002, Minneapolis MN. (in press)
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