Nitrogen from Soybean for Dryland Sorghum
1987
Gakale, L. P. | Clegg, M. D.
Crop and soil data were collected for 2 yr (1984–1985) from a soybean [Glycine max (L.) Merr.]-grain sorghum [Sorghum bicolor (L.) Moench] rotation experiment established in 1974, to evaluate the residual effects of soybean on N uptake, some agronomic characters, and yield of the sorghum crop and residual soil N accumulation. The soil at the experimental site was a Sharpsburg silt clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Fertilizer rates of 0, 56, 112, and 168 kg N ha⁻¹ were applied to the sorghum crop in both the continuous sorghum and rotation cropping sequences. Total N uptake by sorghum was significantly increased by rotation cropping (P<0.05) when the N fertilizer rate was 112 kg ha⁻¹ or less. Sorghum grown in rotation or with the application of 56 kg N ha⁻¹ or more flowered 6.1 days earlier than continuously grown sorghum without N. At the zero level of fertilizer N, sorghum after soybean yielded 85% more grain than did continuous sorghum. Rotation with soybean increased subsequent sorghum grain 14% compared to continuous sorghum when averaged over 2 yr. At or above the 112 kg N ha⁻¹ level, differences between the cropping systems were not different. Estimates of residual soil N as NO⁻₃−N in 1985 showed that after soybean there was 50 to 60 kg N ha⁻¹ more than after continuous sorghum when 56 kg N ha⁻¹ or less had been applied.
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