| Intercropping is one of the tradition planting patterns in China, which increases crop yield and nitrogen utilization efficiency. Therefore it is a common pattern in the arid and semiarid regions in northwest of China. More researches have studies the crop yields and the efficiency of light energy, nutrient and water of intercropping in recent years. However, less studied have evaluated the decomposition characteristics of the straw after returning to the field and its effect on nutrients in soil. There will be two sorts of straws under the legume and cereal intercropping system, ie., the cereal straw with higher C/N ratio and the legume straw with lower C/N ratio. There are some researches to study the effect of the maize or faba beans returning to the soil; but the contribution of both maize and faba beans straw returning to the field has not been studied.Therefore, we had used the methods of field trial and incubations to study the space variation of carbon and nitrogen in soil the recent reclaimed soil under legume-maize intercropping system in Hong Si Pu, Ningxia Hui Autonomous Region; the decomposition characteristics and their effects on nitrogen in soil of maize and faba beans straw added into soil were also evaluated. The main results showed as follows:1. The contents of soil microbial biomass C and N (SMBC, SMBN) in this intercropping soil were high in comparison with single cropping soil. It showed that intercropping system can improve the fertility of soil. Application of N fertilizers significantly increased SMBC and SMBN. Soil microbial biomass C increased significantly as the addition of N fertilizer. The contents of SMBC and SMBN in soil after harvesting maize were significantly higher than harvesting faba bean. The contents of SMBC, SMBN were the highest between lines of faba bean, followed by on lines of maize, and between lines of maize.2. Application of N fertilizers significantly increased the contents of soluble organic C and N (SOC, SON) at faba bean harvest in comparison to the treatment without addition of N fertilizer. And it had no effect on SOC and SON contents at maize harvest. The contents of SOC and SON in soil were the highest between lines of maize, followed by between lines of faba bean, and on line of faba bean, and between lines of maize and faba bean and the lowest were in on line of maize. 3. Additions of maize and faba bean straws increased the soil microbial biomass C (SMBC) and N (SMBN) increased significantly (P<0.05); and the increase rate of SMBC and SMBN in treatments combined addition of maize and faba bean straws was higher than the treatment only added maize straw; it also enhanced the decomposition of straws, and the immobilized N was also released in early time. The ratios of 2:1 and 3:1 of maize to faba bean had better efficiency than other ratios.4. The organic carbon decomposed from the straws was faster than total nitrogen after returning into soil. At the end of the incubation, the organic carbon release rate was 57.05%, but only 33.98% of the total nitrogen was decomposed. This explains the decrease of C/N of straw with increasing of the decomposition times. The treatments with higher C/N ratio immobilized soil nitrogen at the first stage of the incubation. The decomposition characteristics of two crop residues were different among the different proportion of maize and legume returning back into field under the faba bean / maize intercropping system. Additions of maize and faba bean straws promoted the decomposition and nutrition release of straws compared with the treatment only adding one kind of straw; 2:1 was the best ratios of legume and maize. |
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