Soybean Nitrogen Contribution to Corn and Sorghum in Western Corn Belt Rotations

greatest proportion of the beneficial effects of crop rotation, but other factors, including reduced weed, disease, Increased N availability is often associated with the beneficial efand insect problems, can also be important. fects of rotating grain and legume crops. Our objective was to utilize yield response data from two long-term studies to determine the Corn is now commonly grown in a 2-yr rotation with amount of N supplied by soybean [Glycine max (L.) Merr.] for subsesoybean or other similar short-term (2to 3-yr) rotaquent nonlegume crops in 2-yr rotations. The experiments were lotions. As a result, any beneficial effect for growing corn cated in eastern Nebraska (Mead) (rainfed) and central Nebraska in rotation with a legume is highly relevant in today’s (Shelton) (irrigated). Continuous corn (Zea mays L.) and soybean– cropping systems. Some researchers (Baldock and Muscorn cropping systems were present in both experiments while contingrave, 1979; Baldock et al., 1981) have suggested that uous sorghum [Sorghum bicolor (L.) Moench] and soybean–sorghum the N contribution from the legume is responsible for cropping systems were present at Mead only. Three N fertilizer rates most of this beneficial rotation effect to corn, but other were used for the study at Mead and five at Shelton. Nitrogen fertilizer researchers (Russelle et al., 1987; Hesterman et al., replacement values were estimated using graphical and regression 1987) feel this contribution is overestimated. techniques. Results from both techniques indicated that corn in the rainfed experiment at Mead (20 yr) and irrigated experiment at ShelSeveral approaches have been used to determine the ton (10 yr) obtained approximately 65 kg N ha 1 yr 1 from soybean N contribution from the legume in rotations, and the in a 2-yr rotation with soybean at both locations. Sorghum in the different techniques used to estimate the N contribution rainfed experiment at Mead (20 yr) obtained approximately 80 kg to the successive crop could be part of the discrepancy. N ha 1 yr 1 from soybean in a soybean–sorghum rotation. Current LaRue and Patterson (1981) discussed many of these fertilizer N applications based on fall or early-spring soil tests used methods in detail and stated that the fertilizer replaceextensively in this area need to be reduced by these amounts for corn ment value (FRV) and 15N methods to estimate the N and sorghum grown in 2-yr rotations with soybean when grown on contribution to the following crop were among the most mediumto fine-textured soils in the western Corn Belt to reduce commonly used. Bullock (1992) indicates that FRV excess N available for loss and to reduce unnecessary input costs. methodology has probably overestimated the amount of N supplied by the legume. In addition, Ladd (1981) and Harris and Hesterman (1990) using 15N methodolS and farmers have recognized for centuries ogy found that only 15 to 25% of N from the previous the beneficial effects of crop rotations. However, legume cover crops was recovered by the following nonthere is no consensus on the specific causes. Historically, legume crop. cropping systems with various crop species grown in Using the FRV method, results have varied from sequences of differing lengths were widely used because those similar to Ding et al. (1998) where they found crops were shown to produce more biomass and grain that soybean supplied 30 kg N ha 1 to a following corn when grown in rotation. In more recent times, usage of crop in Ontario while Bundy et al. (1993) found no crop rotation in production systems has ebbed and consistent amount of N supplied to the following corn flowed in the USA as farm programs and technology crop by soybean in Wisconsin. Other problems with the changed. The substantial increase in availability of synFRV method include species differences regarding the thetic fertilizers and pesticides during the 1950s and amount of N supplied to subsequent nonlegume crops. early 1960s induced many farmers to switch to monoculBlevins et al. (1990) reported that legumes provided 65 ture production systems, which they felt could forever to 75 kg N ha 1 to corn and 125 to 135 kg N ha 1 to replace crop rotation without loss in yield (Bullock, sorghum using the FRV method. In contrast to the FRV 1992). Since that time, opinions have changed, and crop method, the 15N method is far more resource intensive. rotation has again become a desirable strategy in crop Specialized and costly fertilizer (15N-tagged) and analytiproduction systems. Bullock (1992) cited many examcal tools (mass spectrometer) must be used to obtain ples of different types of crop rotation systems used data required to calculate N contributions from legumes both in the USA and around the world and their benefiusing 15N tracers. This being the case, very few data are cial effects on crop yields. He also noted that many of available using 15N to construct a general consensus on the factors and mechanisms responsible for the so-called the legume N contribution, especially from long-term rotation effect are not completely understood. Nitrogen experiments conducted for many years covering varying availability is usually identified as responsible for the environmental conditions. On the other hand, FRV can be computed with relatively easy-to-gather data (yield USDA-ARS and Dep. of Agron., Univ. of Nebraska, Lincoln, NE of a nonlegume crop over a series of N fertilizer rates 68583. Joint contribution of USDA-ARS and the Nebraska Agric. in both monoculture and rotation with a legume). These Res. Div., Journal Ser. no. 13821. Received 30 Aug. 2002. *Corredata are frequently collected in cropping system experisponding author ([email protected]). ments. Therefore, estimates using the FRV can be made Published in Agron. J. 95:1220–1225 (2003).  American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: FRV, fertilizer replacement value.