Marginal effect of soybean and peanut intercropped withmaize in upland red soils

To understand the marginal effect of leguminous crops in intercropping systems of maize, chlorophyll content, leaf area index, root dry weight, root nodule, agronomic traits and yield of border-row soybean and peanut were determined under low nitrogen (50 kg·hm²) fertilized soybean-maize and peanut-maize intercropping systems. The field experiment was carried out in the Upland Red Soil Experimental Station of Jiangxi Agricultural University for the period from Jul. 28, 2011 to Nov. 20, 2011. The results showed that the chlorophyll content of the first and second border-rows of intercropped soybean and peanut was higher than that of the mono-crop system at different growth stages with/without nitrogen fertilization. However, no obvious differences were noted in chlorophyll content between the third border-row of intercropped and mono-cropped soybean and peanut. While leaf area index of the first and second border-rows of intercropped soybean and peanut increased at different growth stages, no obvious change was noted in the third border-row, compared with the mono-cropped soybean and peanut. Also the effect of nitrogen fertilization under the mono-cropped was greater than that of the intercropping. Root dry weight of the first and second border-rows of intercropped soybean increased by 14.7% and 2.8% and those of intercropped peanut increased by 16.5% and 3.1%, respectively, compared with mono-cropped soybean and peanut under no nitrogen fertilization. Root dry weight of the first and second border-rows of intercropped soybean increased by 11.3% and 1.3% and those of intercropped peanut increased by 13.5% and 4.6%, respectively, compared with mono-cropped soybean and peanut under nitrogen fertilization. The third border-row of intercropped systems showed no obvious difference from mono-cropped. Nitrogen fertilization under mono-cropping showed greater effect than intercropping. Intercropping also increased per-plant root nodule number and weight of the first and second border-rows of intercropped soybean and peanut at maturity stage. It, however, showed no obvious effect on the third border-row and 50 kg·hm^-2 nitrogen fertilization decreased root nodule number and weight. Nitrogen fertilization and intercropping improved agronomic traits of soybean and peanut, with the most significant marginal effect of the first border-row. The economic and biological yields per plant and yields per row of the first and second border-rows of intercropped soybean and peanut were higher than those of mono-cropping system with/without nitrogen fertilization. The first border-row presented the highest value, while the values of the third border-row were not obviously different from those of the mono-cropping system. Furthermore, the effects of nitrogen fertilization on agronomic traits and yield of soybean and peanut were greater than those of intercropping system. The study therefore showed that marginal advantages of intercropping was the first border-row > the second border-row > the third border-row ≈ mono-cropped system. The effect of nitrogen fertilization was greater than intercropping.