Source of the soybean N credit in maize production

• Published in: Plant and soil 2001-10, Vol.236 (2), p.175-184
• Main Authors: Gentry, L.E., Below, F.E., David, M.B., Bergerou, J.A.
• Format: Article
• Language: English
• Subjects: Accumulation; Agricultural soils; Agrology; Agronomy. Soil science and plant productions; Biological and medical sciences; Corn; Corn belt; Crop management; Crop production; Crop residues; Crop yield; Cropping systems. Cultivation. Soil tillage; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Generalities. Cropping systems and patterns; Grains; Mineralization; Nitrogen; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Plants; Residual soils; Soil samples; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; Soybeans; Tillage
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/A:1012707617126

Nitrogen response trials throughout the United States Corn Belt show that economic optimum rates of N fertilization are usually less for maize (Zea mays L.) following soybean (Glycine max L.) than for maize following maize; however, the cause of this rotation effect is not fully understood. The objective of this study was to investigate the source of the apparent N contribution from soybean to maize (soybean N credit) by comparing soil N mineralization rates in field plots of unfertilized maize that had either nodulated soybean, non-nodulated soybean, or maize as the previous crop. Crop yields, plant N accumulation, soil inorganic N, and net soil mineralization were measured. Both grain yield (6.3 vs. 2.8 Mg ha⁻¹) and above-ground N accumulation (97 vs. 71 kg ha⁻¹) were greatly increased when maize followed nodulated soybean compared with maize following maize. A partial benefit to yield and N accumulation was also observed for maize following non-nodulated soybean. Cumulative net soil N mineralization following nodulated soybean, non-nodulated soybean, and maize was 112, 92 and 79 kg N ha⁻¹, respectively. Net mineralization of soil N appeared to be influenced by both quality (C:N ratio) and quantity of residue from the previous crop. In addition to an increase in plant available N from mineralization, the amount of soil inorganic N (especially in soil 5 cm from the row) was greater following nodulated soybean than non-nodulated soybean or maize. Based on these data, the soybean N credit appears to result from a combination of a decrease in net soil mineralization in continuous maize production and an increase in residual soil N from symbiotic fixation.