Abstract:

In order to improve soil fertility and make full use of straw resources, the effect of straw returning to fields by wet harrow in autumn on the stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in rice leaves and soil and their relationships with rice yield were explored. The experiment was carried out in Panjin City, Liaoning Province,China, with a random block design. Three treatments were set as no straw returning to the field (CK), one-year straw returning to the field by wet harrow in autumn (S1), and two consecutive years of straw returning to the field by wet harrow in autumn (S2). The C, N, P contents in rice leaves and soil at different growth stages were determined, and their stoichiometric ratios were calculated. The results showed that the soil organic carbon content under S1 and S2 treatments was significantly (P<0.05) increased by 8.71% and 28.36%, respectively, compared with the CK treatment. Soil total phosphorus content under S1 and S2 treatments at each growth stage was significantly higher than that under CK, and the soil total nitrogen content under S2 treatment was significantly higher than that under CK at tillering stage and maturity stage. The soil C/P ratio under S1 treatment was significantly decreased at each growth stage as compared with CK. However, the soil C/P ratio under S2 treatment was only significantly lower than that of CK at the jointing stage. The soil N/P ratio ranged from 2.02 to 2.74. Except the maturity stage, the soil N/P ratio among treatments signifiantly increased as S1<S2<CK at the other growth stages. The C, N, P contents of rice leaves were not significantly affected by straw returning, and the leaf N/P ratio ranged from 8.68 to 11.50. The leaf C/N raito and C/P raito were significantly positively correlated with soil organic carbon and total nitrogen. The theoretical yield and actual yield of rice under S2 treatment were significantly increased compared with those under CK. Rice yield was significantly (P<0.01) positively correlated with soil organic carbon, soil total nitrogen, soil C/P ratio and soil C/N ratio, but was not significantly correlated with the ecological stoichiometric characteristics of rice leaves. In conclusion, short-term continuous straw returning to the fields by wet harrow in autumn could improve soil nutrients contents and rice yield. But, the relatively lower N/P raito in rice leaves and soil indicated that the rice growth in the experimental conditions was limited by N. Therefore, nitrogen fertilizer management should be oprimized on the basis of straw returning to ensure stable and increased rice yield.

Key words: rice straw returning to fields by wet harrow in autumn, rice, soil, ecological stoichiometry