H. P. Johnson

Soil and Water Loss from Conservation Tillage Systems

ABSTRACT A rainfall simulator was used to evaluate the effects of six different tillage practices on soil and water losses from continuous corn for three soils in Iowa. Soil loss decreased as tillage decreased. Percent of soil covered by corn residue explained between 78 and 89 percent of the variance in erosion among tillage systems. The effect of non-uniformly distributed corn residue on controlling erosion was greater than expected based on a published mulch factor. Runoff amounts decreased as residue cover increased for two of the three soils studied. No critical slope length limits were found for the tillage practices, soils, slopes, and slope lengths studied except for till-planting on the Ida soil. As sediment concentra-tions increased, mean sediment size increased for one soil, decreased for a second soil, and was unrelated to sediment concentration for the third soil.

The Effect of Tillage Systems on Pesticides in Runoff from Small Watersheds

ABSTRACT RUNOFF losses of fonofos (insecticide), alachlor, atrazine, and cyanazine (herbicides) with sediment and water were measured under natural rainfall con-ditions for six small watersheds planted to continuous corn with conventional, till-plant, and ridge-plant tillage systems. Losses were very dependent on the time between pesticide application and the first runoff event. Soil sampling indicated that pesticide half-lives were about 2 wk (except for atrazine, 1 to 2 months), with pesticides remaining concentrated in the top 5 cm. Not quite 50 percent of the average fonofos loss was with water, whereas from 80 to 90 percent of the average herbicide losses were with water. Decreased runoff and erosion for the till-plant and ridge-plant tillage systems relative to conventional resulted in decreased pesticide losses, but pesticide concentrations in sediment and (or) water were sometimes higher for conservation tillage systems.

Tillage System Effects on Sediment and Nutrients in Runoff from Small Watersheds

ABSTRACT TWO conservation tillage systems were studied and compared with the conventional (plow-disk-plant) tillage system. Runoff, soil loss, and nutrient losses dur-ing the 1973-75 growing seasons were measured for six small, paired watersheds planted to continuous corn (runoff and soil loss for the year, 1972, when conservation tillage systems were being established were also measured). Fifty-nine percent of the soil surface under ridge-planting and 11 percent under till-planting were covered with crop residue, compared to less than 2 per-cent for conventional planting. Conservation tillage systems on the average reduced runoff about 40 percent and reduced soil loss from 60 to 90 percent. Total losses of nitrogen and phosphorus (total P in sediment measured only in 1973) were mostly associated with soil loss and consequently were decreased for conservation tillage systems. Solution phosphorus losses and concen-trations and available P concentrations in sediment (measured in 1974 and 1975) increased with residue cover. Several factors could be responsible, including decreased fertilizer incorporation, selective erosion pro-cesses, and the residue being a phosphorus source. Corn yield data are given.

Drainage Needs and Returns in North-Central Iowa

CURRENT status of drainage and estimated drainage needs of the soils in the Des Moines River basin as indicated from an extensive survey are presented. A high percentage of the area has the potential for receiving benefits by improving county mains and on-the-farm drainage. Analyses have been made of the economic potential for drainage improvements by comparing three drainage input levels. Benefit-cost ratios indicate drainage of very poorly drained and poorly drained soils is a good investment for corn and soybean production..

Comparison of Simulated and Measured Nitrate

ABSTRACT A hydrologic and nitrate-transport simulation model was developed and used to simulate the major water and nitrogen-transport processes occurring in a typical agricultural watershed during the crop growth period. Data from a tile drainage experiment were used to evaluate the simulation model. Predicted values of tile flow volumes and nitrate concentrations in the tile effluent were compared with the measured data and, although variable, were encouraging. Deviations between predicted and measured nitrate losses in the tile effluent existed on a daily basis but usually were small when considered over the entire crop growth period.

Simulated Effects of Fertilizer Management on Nitrate Loss with Tile Drainage Water for Continuous Corn

ABSTRACT Acomputer simulation model was used to estimate the impact of different fertilizer management practices for continuous corn production on the loss of nitrate-nitrogen with tile drainage water. Simulations using historical weather data were conducted for seven consecutive growing seasons for a location in Iowa. Currently, nitrogen management by most farmers in Iowa can be represented by a single application (usually NH3-N) of about 150 kg/ha. Management schemes tested to improve the efficiency of nitrogen use include fertilizer application rates, and timing and the number of applications. Model results indicate that lower application rates and multiple applications significantly decrease nitrate-nitrogen losses in both wet and dry years

Transport of nitrate and gaseous denitrification in soil columns during leaching

Abstract Leaching of nitrate with first-order denitrification in a soil column of finite length has been theoretically analyzed. Transport equations and boundary conditions describing the movement of nitrate and denitrification, by chemical and/or microbiological means, in a soil column were set up and solved for continuous application of nitrate at the soil surface. From the mathematical model presented, relative concentration profiles can be determined for any time and known values of the diffusion coefficient and average solute velocity. The validity of this model has been supported by comparison of the results with experimental data from the literature.

Particle Movement and Separation Phenomena for a Gravity Separator: I. Development of a Markov Probability Model and Estimation of Model Parameters

ABSTRACT THE complexity of gravity separator mechanics precludes the use of a deterministic model for particle movement on a gravity separator. Particle movement is examined as a stochastic process; a distance-transition Markov probability model for particle movement is proposed. A linear programming method for estimation of the Markov model parameters is explained.

A Water-Balance Model for Deep Loess Soils

ABSTRACT A digital computer model was developed to simulate the moisture balance on an agricultural watershed, including interception, infiltration, surface-depression storage, surface runoff, soil moisture redistribution, deep percolation, and evapotranspira-tion. The model is for small homogeneous watersheds on deep, well-drained soils, and was calibrated and tested using data from small research watersheds operated in the deep loess hills in western Iowa. The model produced continuous simulation of the moisture balance during the growing season. The correla-tion between measured and predicted surface runoff depths for individual events during 4 yr of records was 0.80. The correlation between predicted soil moisture in the root zone and bi-weekly measurements during the same 4 yr was 0,91.

Stochastic modeling of granular flow in seed sorting

The complexity of gravity separator mechanics precludes the use of a deterministic model for particle movement on a gravity separator. Particle movement is examined as a stochastic process; a distance-transition Markov probability model for particle movement is proposed. A linear programming method for estimation of the Markov model parameters is explained.