Agricultural soils undergo periods of saturation followed by desiccation throughout the course of a growing season. It is believed that these periods of wetting and drying influence soil structure and may affect the rate of soil detachment. Thus, an experiment was conducted to investigate the influence of a disturbed soil (soil sieved to simulate tillage) subjected to various wetting and drying cycles, on soil bulk density and the resistance to soil detachment with runoff. Seven treatments consisting of wetting and drying cycles ranging from 0 to 6 cycles were evaluated under laboratory conditions using an experimental flume apparatus. A Richards growth model proposed for predicting the influence of wetting and drying on soil detachment was also evaluated. Results showed that the soil bulk density increased as the number of wetting and drying cycles increased. The soil detachment rate decreased as the number of wetting and drying cycles increased. Moreover, initial soil detachment (occurring as soon as runoff began) rates were high for 1 to 3 wetting and drying cycles, while the rate of initial detachment decreased after the third cycle. For example, soils with two and three wetting and drying cycles took 6.5 and 7 min to reach the maximum 1 cm souring depth, respectively, while the soils subjected to four or more wetting and drying cycles did not reach the maximum 1 cm depth during the 15 min runoff experiment. In addition, the proposed S-Shaped Richards growth model was a good predictor for estimating the soil detachment of soils experiencing various wetting and drying cycles. Findings from this study suggest that more attention should be given to the influence that soil wetting and drying have on the prediction of soil detachment. Information from this study is expected to be useful for improving soil management strategies for reducing soil erosion.

Optimal yield of corn fertilized with poultry litter (PL) may be achieved with less PL if applied by subsurface banding (LSS). The objective of this study was to determine, using economic analysis, if profit maximizing PL rate can be reduced if applied by LSS relative to the conventional surface broadcast (LBC) in corn production. Corn was grown with six PL rates ranging from 4.4 to 27.0 Mg ha⁻¹ applied by LSS or LBC and with seven synthetic N (sN) rates ranging from 0 to 292 kg ha⁻¹. Rates of PL or sN that maximized yield or profit were determined from yield response curves. The results showed that yield maximizing PL was greater than profit maximizing PL by as much as 25% regardless of the application method showing that targeting maximum yield is wasteful and may reduce profit. Both yield and profit maximizing PL rates were less if applied by LSS than by LBC while the respective yields did not differ greatly. As much as 17% more grain was produced by 1 Mg ha⁻¹ profit maximizing PL if applied by LSS than by LBC. Availability of N from PL was 40% if applied by LSS. These results show that applying PL by subsurface banding conserves N, leads to greater grain yield per 1 Mg PL, and thus the same corn yield may be obtained with less PL if applied by banding than by surface broadcasting.