Phosphorus Management

a significant relationship was found between soluble P loss in runoff and soil test P. Eghball and Gilley (2001) Soils with high levels of P can contribute to excess P in runoff and found that erosion was the most important factor in subsequently pollute the surface water. Excess P in the soil can be removed from the system by harvesting crops. The objectives of this loss of total and particulate P, whereas runoff amount, study were to evaluate corn (Zea mays L.) P removal effects on tillage, and P source were the important factors influencsoil P reduction, and to evaluate various corn hybrids and soybean ing loss of dissolved and bioavailable P in runoff. The [Glycine max (L.) Merr.] varieties for differences in grain P concentrasoil test P levels in this study did not seem to be high tion and P removal. Soil with varying P levels as a result of annual enough (ranged from 25 to 101 mg kg 1 in the top 5 cm or biennial beef cattle (Bos taurus) feedlot manure or compost applisoil) to influence dissolved or bioavailable P in runoff. cation was cropped to corn for 4 yr without any P addition. In other Soils with high P test concentrations can be managed studies under various water and N regimes, corn hybrids and soybean varieties were evaluated for grain P concentration and P removal. to reduce the soil test P level and the subsequent reducFour years of corn production without P addition lowered surface tion for P loss potential in runoff. Crop, soil, and mansoil (0–15 cm) extractable P level (Bray and Kurtz no. 1) from 265 mg agement factors can change soil test P (Pierzynski and kg 1 to 171 mg kg 1 in the biennial N-based compost treatment. Based Logan, 1993). Practices such as deep tillage to bury the on a decay equation, it would have required 10 yr of corn P removal high P containing surface soil, crop P removal, and P to lower the soil P level to the original 69 mg kg 1 that existed before application strategies can be used to reduce soil P level. treatment application. The rate of decrease in extractable soil P was However, tillage can increase soil erosion and hence greater when soil P was higher and reduced with decreasing soil P result in greater total P loss in runoff (Eghball and level. Most of the P in the plants was absorbed from the 0to 15-cm soil depth since no significant reduction in soil P level was observed Gilley, 1999). The build-up and maintenance P applicafrom 1996 to 1999 in the 15to 30-cm soil depth. Across 2 yr, there tion strategy can increase soil test P while the sufficiency was as much as 54% difference among corn hybrids for grain P restrategy (apply only what is needed) can maintain soil moval. The differences in P concentrations among corn hybrids inditest P near the original level (Olson et al., 1982). Crop cated that hybrids could be selected for low P uptake when lower removal can be an effective method of reducing soil test P level in ethanol production by-product or in animal ration and P. The amount of P removed by grain from the soil subsequently in manure is desired. Soybean grain P concentration depends on the crop grown. McCallister et al. (1987) was nearly twice that for corn but grain P removal was less for soybean found that soil test P in surface layers (0–15 cm) of two than for corn. Crop P removal can significantly reduce soil P level with time. Mollisols under irrigated corn decreased by 42% while soil test P in two other Mollisols under fallow–winter wheat (Triticum aestivum L.) did not decline following A of manure or composted manure can 20 yr of cropping without any P addition. McCollum result in a significant accumulation of P in soil. (1991) showed that high soil test P ( 50 mg kg 1, MehEghball and Power (1999) found that N-based applicalich-1) could not be maintained by annual replacement tions of manure and composted manure resulted in a of crop-removed P because P conversion to unavailable significant P increase in the soil while P-based applicaforms was a larger factor than crop removal in depleting tions maintained the soil P near the original level. High the extractable P pool in an Ultisol. However, when P levels of plant-available P in the soil can result in signifilevel was 20 to 24 mg kg 1, soil test P was maintained cant P loss in runoff (Pote et al., 1996). How much soil by band application of crop-removed P. Grain P removal test P influences the P loss in runoff depends on the by corn, soybean, and winter wheat increased as the time of P application. Eghball et al. (2002) showed that fertilizer P application rates increased from 0 to 54 kg soil test P was not a significant factor in soluble P loss ha 1. This occurred even though yield was maximized in runoff when application of manure or inorganic fertilat about 11 kg P ha 1 in a 25 yr P buildup–decline study, izer was made just before simulated rainfall. In contrast, indicating luxury consumption of P by crop when soil when manure or P fertilizer was applied a year earlier, test P was high (Barber, 1979). Genotypes of each crop can remove different amounts of P from the soil. GorUSDA-ARS, Dep. of Agronomy and Horticulture, Univ. of Nebraskadon et al. (1997) found differences among corn hybrids Lincoln, Lincoln, NE, 68583. Joint contribution of USDA-ARS and for total P uptake in a no-till rainfed system. Univ. of Nebraska Agric. Res. Div., Lincoln, NE, as paper no. 13763. The objectives of this study were (i) to evaluate corn Received 10 July 2002. *Corresponding author (BEGHBALL1@ unl.edu). grain P removal effects on soil test P in a soil with a history of manure and composted manure applications Published in Agron. J. 95:1233–1239 (2003). and (ii) to evaluate differences among corn hybrids and  American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA soybean varieties for grain P concentration and removal.