Excretion of nitrogenous compounds by the root system of peanut intercropping with rice at different growth stages

Recent success in cultivation of rice plants in aerobic soil makes rice plant intercropping with legumes possible.A previous study has shown an obvious yield advantage and nitrogen(N) transferring from antecedent peanut to rice in a peanut and rice intercropping system.Sand-culture and solution-culture experiments were carried out to study the(excretion) of nitrogenous compounds of peanut roots intercropped with rice at different growth stages(seedling,flowering and pod-filling stage of peanut).Considerable amounts of extraction of nitrogenous compounds were observed at the growth stages,with the highest amount recorded at flowering stage.The N(including NO3-,NH4+ and total nitrogen) (excretion) rate in the morning was the highest at seedling stage.The concentrations of NO3- and NH4+ of rice monocropping,(intercropping) and peanut monocropping treatments in sand-culture experiment were 1.415,5.044,and 2.140(mg/L) and 0.0482,0.332,and 0.132 mg/L,respectively,while under water cultivation condition,for different cropping practices,they were 0.0726,0.743,and 0.181 mg/L and 1.036,1.709,1.736 mg/L,respectively.However,the highest excretion of N was recorded during the afternoon at flowering stage,and it was in the evening at the pod-filling stage.At flowering stage,the total N concentrations of rice monocropping,intercropping and peanut monocropping treatments were 15.487,21.530,and 10.906 mg/L in sand-culture experiment,respectively,but under water cultivation way,they were 4.204,5.445,and 3.813 mg/L,respectively.Composition of the N forms examined as NO3-,NH4+ and total N,was found to be changeable during the growth stages,suggesting that the major pathways of excretion are possibly different at different plant ages.Our results also showed that extraction amounts of different N forms were variant under different cultivation conditions.The N extretion under sand-culture was far higher than that under solution-culture,indicating that the N excretion was stimulated by mechanical resistance of the culture medium,which in turn enhanced the plant N uptake.