Effect of Peanut Roots Intercropped with Rice on Excretion of Nitrogenous Compounds at Different Growth Stages

Abstract

Sand-culture and solution-culture experiments were carried out to study the excretion of nitrogenous compounds by peanut roots intercropped with rice cultivated in aerobic soil at different growth stages, i.e., seedling, flowering and pod-filling stage of peanut crop. Considerable amounts of nitrogenous compounds were excreted at all the growth stages, with the highest amount recorded at flowering stage. Maximum nitrogen (including NO3 −, NH4 + and total nitrogen) excretion rate at seedling stage was detected in the ‘morning’. The concentrations of NO3 − and NH4 + of rice monocropping, intercropping and peanut monocropping treatments in sand-culture experiment were 1.415, 5.044, 2.140 mg L− 1 and 0.0482, 0.332, 0.132 mg L− 1, respectively, while they were 0.0726, 0.743, 0.181 mg L− 1 and 1.036, 1.709, 1.736 mg L− 1, respectively, in solution culture experiment. However, the maximum excretion of nitrogen was recorded during the ‘afternoon’ at flowering stage, and it was in the ‘evening’ at the pod-filling stage. At flowering stage, the total nitrogen concentrations of rice monocropping, intercropping and peanut monocropping treatments were 15.487, 21.530, 10.906 mg L− 1 in sand-culture experiment, respectively, and they were 4.204, 5.445, 3.813 mg L− 1, respectively, in solution-culture experiment. Composition of the nitrogen forms examined as NO3 −, NH4 + and total nitrogen, was found to be changeable during the growth stages, suggesting that the major pathways of excretion are possibly different at different plant ages. Different amounts of nitrogenous compounds were recorded in the two culture experiments and the amounts of nitrogenous compounds in sand-culture were far higher than those in solution-culture experiment, inferring that mechanical resistance of the culture medium could stimulate the excretion of nitrogenous compounds.