Managing livestock manure for profitability and water quality protection

The Manure Management interdisciplinary research issue team formed in 1990 to study several issues related to Iowa\u27s rapidly accel­ erating increase in animal production, both in the number and size of animal units, particu­ larly swine units. Swine facilities being built in Iowa today include a number of 3,500-head farrowing units and 15,000-head (and larger) finishing units. The poultry industry has also grown rapidly. Economic pressures have caused animal production systems to become larger and more concentrated, requiring sig­ nificant capital investment. This concentra­ tion has occurred at the family farm level as well as in production systems controlled by large agribusiness firms. One disturbing trend is the increase in family farm units that do not own the animals they are producing

Soil Compaction Problems of 1993

The 1993 crop season will be one that few Iowa farmers will forget. Excess precipitation was common from the last half of 1992 and throughout the entire 1993 cropping season. There has been an increased concern over soil compaction problems throughout this season, and what these problems may create for the 1994 crop year. The objective of this paper will be to review how and why the problem has occurred and what should be done, if anything, to minimize the problem in 1994

Soil Compaction Research Summary

Soil compaction has become a major topic of discussion among scientists and crop producers in recent years. Even though some producers consider soil compaction to be a problem on their own farms, they feel resigned to the fact that there is little they can do to control it. Some recent solutions have been offered based on research efforts with soil compaction. There is significant interest in developing crop production systems with controlled traffic to help control the problem of soil compaction. There have also been new machine developments to address the problem of soil compaction, particularly with rubber tracked equipment and lower pressure tires

Comparison of Simulated (DRAINMOD) and Measured Tile Outflow and Water Table Elevations From Two Field Sites in Iowa

Four years of field data on subsurface drain flows and water table elevations from two experimental sites in Iowa were used to compare the predicted values by DRAINMOD, a water management model. DRAINMOD simulations conducted for Nicollet silt loam and Kenyon loam soils of Iowa predicted water table elevations within an average deviation of 15 cm and 19 cm, respectively. The subsurface drain outflows predicted by DRAINMOD were within an average deviation of 0.065 cm/day

Simulating Corn Yields for Two Iowa Soils

Corn yields in Iowa often could be improved with better water table management practices, but many soils in this region do not have adequate information about their yield potential. This study was conducted to evaluate the applicability of DRAINMOD in simulating crop yields for artificially drained soils of central and northeastern Iowa. Ten years of field data on crop yields from two drainage experimental sites in Iowa were used to compare relative crop yields with yields predicted by DRAINMOD. Data on saturated hydraulic conductivity, soil-moisture tensions, soil infiltration, and other physical properties were collected either at the experimental sites or in the laboratory on disturbed soil samples. Data on upward flux and infiltration constants for the Green and Ampt equation were calculated by using the infiltration data and soil-moisture retention characteristics of the surface layer. Relative crop yields predicted by DRAINMOD were reasonably close to the observed relative yields for both Iowa sites. Standard error of the estimates of relative yields was 17.41% and the average deviation was 12.99%. The coefficient of determination, r2, between the predicted and measured yields was 0.54. Overall performance of the model suggests that DRAINMOD can be used successfully for predicting yields for different locations if data on site characteristics, soil-water properties, and plant growth functions are available

Spatial Analysis of NO 3 -N Concentration in Glacial Till

Analysis of the spatial variability of groundwater NO3 –N concentration is a logical step for a meaningful groundwater quality assessment, for mapping out areas of environmental concern, and for developing appropriate management schemes in a glacial till aquitard. This study was conducted to characterize the spatial variability of NO3 –N concentration in shallow (\u3c6.0 m) and deep (\u3e6.0 m) groundwater in a 12–ha. glacial till aquitard and to estimate NO3 –N concentration in unsampled locations. Omnidirectional and directional semivariogram analysis, statistical anisotropy analysis, and model fitting were performed for average and extreme monthly groundwater NO3 –N data. Results indicated a weak spatial structure of NO3 –N concentration for both shallow and deep well data. However, the best–fitted variogram models generally performed satisfactorily during cross validation, yielding a mean reduced error of –0.01 to –0.074 and reduced variance of 0.6 to 2.18. Untransformed shallow–well NO3 –N exhibited a lower range of correlation than deep–well data. Statistical anisotropy was found to coincide with the general groundwater flow directions for the average and maximum observed NO3 –N concentrations in shallow wells. Geostatistical estimation using ordinary kriging indicated relatively higher NO3 –N concentrations at the down–gradient areas for shallow wells and at regions close to nitrogen fertilizer application sites for the deep wells. With satisfactory cross–validation performance of the variogram models, the geostatistical results of this study may be used as basis for estimating spatially variable NO3 –N loading rates in the glacial till aquitard

Tillage and crop rotation effects on subsurface drainage response to rainfall

A field study was conducted to determine if tillage and crop rotation affected subsurface drainage response to rainfall. An instrumentation system collected subsurface drain flow data from thirty-six, 0.4 ha plots during the 1993, 1994 and 1995 growing seasons. Response time, time-to-peak drain flow rate, drainage volume, peak drain flow rate and percent preferential flow were compared between two tillage systems (no-till and chisel plow) and two crop rotations (continuous corn and corn-soybean) for 23 drainage events over the three-year study. The influence of preferential flow was estimated for each drainage event using a hydrograph separation procedure based on subsurface drain flow rate changes