Study on decomposition of maize straw under different green manure cropping patterns

【Objectives】 Maize (Zea mays L) is the largest grain crop in China, how to treat large amount of maize straw is one of key problems. Studying the effect of different winter green manure on the decomposition of maize straw is very important for the development of sustainable agriculture.【Methods】 We used nylon bags under four different green manure cropping patterns winter fallow (YCK), Medicago sativa L.(YZ), Lolium perenne L.(YH), Raphanus sativus L.(YL) to assess residue decomposition dynamic and major nutrients release carbon (C), nitrogen (N), phosphorus (P) and potassium (K)of maize straw within 177 days in red soil.【Results】 The decomposition and nutrient release rates in maize straw were fast in the early stage and slow in the later stage under the four different green manure cropping patterns. The maximum decomposition and nutrient release rates both appeared at the 7th day after the maize straw was plowed into the red soil. At the 177th day, the cumulative decomposition amounts in the maize straw were 23.41, 21.22, 20.86 and 20.95 g respectively under four green manure cropping patterns(YCK, YZ, YH, YL), and compared to YCK, YZ, YH and YL treatments were significantly decreased by 9.3%, 10.9%, 10.5% respectively; the cumulative carbon release amounts were 12.38, 11.07, 11.18, 11.36 g respectively, were also significantly reduced by 10.6%, 9.7% and 8.3% respectively under the three treatments, compared to YCK. The cumulative N release amounts under each treatment were 479.46, 513.04, 442.58 and 530.20 mg respectively, compared with YCK, there was no significant difference under green manure treatments; but the cumulative N release amounts under YH was 13.7% and 16.5% lower than that under YZ and YL. For phosphorus, the cumulative release amounts were 58.10, 57.91, 58.47 and 59.47 mg respectively, YL treatment significantly increased by 2.35% compared to YCK. At the 28th day, the cumulative release amount of K in each treatment was 487.20, 444.85, 456.94 and 434.55 mg, the cumulative release amount of K under YCK reached 100%, those under YZ, YH and YL reached 91.31%, 93.79% and 89.19% respectively, which were significantly decreased compared to the YCK, all the treatments released K completely at the 42th day. The C/N, C/P and C/K ratios in the maize straw in the YZ, YH and YL were significantly higher than that in the YCK at the 177th day.【Conclusion】 The maximum rates of the cumulative decomposition and nutrient release in the maize straw appear at the 7 days and get slow in the later time. Planting green manure can significantly slow down the decomposition rate of maize straw and release rates of C and K; cultivating Medicago sativa L.(YZ) and Raphanus sativus L.(YL) can promote N release of maize straw, Lolium perenne L.(YH) can inhibit maize straw N release, Raphanus sativus L.(YL) could significantly promote P release. Planting Raphanus sativus L. not only can promote N release, but increase the effectiveness of phosphorus in the red soil. While it can reduce the rate of potassium release from maize straw, make the straw potassium more effective. So that, considering of improving soil fertility and reasonable straw nurients release, Raphanus sativus L is the better winter green manure after the maize harvested.