Effects Of Straw Residue Returned And Nitrogen Application Rates On Yield Formation Of Rice

There are many reports to date regarding the effects of wheat straw incorporation to soil on nutrient cycling in paddy field, soil improvement, field ecology and rice grain yield. However, little information is available on dry matter (DM) production and distribution, and nitrogen (N) uptake and utilization. To investigate the impacts of straw residue returned and N management on rice yield and its components, DM production and distribution, as well as N uptake and utilization, we performed an experiment at Dapu Town (31°17.5N, 119°54.0E), west of Taihu Lake, Yixing City. A middle-maturing late japonica cv. Wuging 15 was grown at three levels of N supply (0 kg N·ha-1, ON; 200 kg N·ha-1, LN; 270 kg N·ha-1, NN) and three treatments of straw residue returned (no straw applied, M0; 3750 kg·ha-1 wheat straw chopped and incorporated with the soil of the plough layer; M1; 3750 kg·ha-1 wheat straw chopped and buried in ditches, M2). The results obtained here are expected to provide some guidelines in technique of all straw residue returned. Results showed as follows:1. Effect of straw residue returned and N application rates on grain yield of rice. (1) Compared with M0, treatments with straw residue returned showed non-significant increases in grain yield in 2004 growing season when rice crops experienced less rain during the vegetative and grain-filling stages and lower temperature during the grain-filling stage, as well as in 2006 growing season when rice plants were grown with more rain during the vegetative and grain-filling stage, as well as higher temperature and less rain during the vegetative and reproductive phases, with the magnitude of increases being larger for M1 than M2 treatment. In contrast, treatments with straw residue returned showed non-significant yield loss in 2005 growing season when lower temperature and more rain during the vegetative and reproductive phase, together with less sunlight across the whole growth duration, were experienced by rice corps. (2) Grain yield increased significantly with N supply from 0 to 200 kg N·ha-1 (LN), but further increases in N supply to 270 kg N·ha-1 (NN) resulted in no significant increase. (3) Maximum grain yield was reached by the combination of M1×NN or M1×LN in 2004, M0×LN in 2005, and M1RLN in 2006, respectively.(4) Interaction between M and N was not observed for grain yield per unit area.2. Effect of straw residue returned and N application rates on yield components of rice. (1) Compared with M0, M1 treatment increased panicle number per unit area by 1.03%, 2.48% and 5.73% in 2004, 2005, 2006 growing seasons, respectively; M2 increased panicle number per unit area by 1.37% in 2004, but decreased by 0.22% and 2.69% in 2005 and 2006, respectively, as compared with M0; Panicle number per unit area increased significantly with increasing N application rate. (2) Compared with M0, M1 treatment increased spikelet number per panicle by 1.03% in 2004, but decreased by 8.47% and 5.11% in 2005 and 2006 respectively; M2 increased by 3.86% and 2.89% in 2004 and 2005 respectively, but decreased by 4.27% in 2006, as compared with M0. Spikelet number per panicle increased obviously with increasing N supply. (3) Compared with M0, filled grain percentage decreased by 1.81%, 2.59% in 2004, 0.80% and 2.51% in 2005 for M1- and M2-treated plants, respectively, but increased by 1.61% and 0.17% in 2005, for M1-and M2-treated plants, respectively. Filled grain percentage decreased obviously with increasing N supply. (4) Compared with plants with straw removed (M0), 1000-grain weight decreased by 1.72%, 0.75% in 2004 for M1- and M2-treated plants, respectively, but increased by 1.61% and 0.17% in 2005, 2.75% and 0.59% in 2006 for M1-and M2-treated plants, respectively. 1000-grain weight decreased obviously with increasing N supply. (5) M×N interactions were not detected for panicle number per unit area, spikelet number per panicle, filled-grain percentage, 1000-grain weight and spikelet number per unit area.3. The effect of straw residue returned and N application rates on biomass yield and economic coefficient. (1) As compared with M0, M1 treatment showed 98.80, -49.43, 66.36 g·m-2 higher biomass yield (relative increases 6.68%, -3.21%, 4.47%) in 2004, 2005 and 2006, respectively, and M2 treatment showed 11.82%, -52.12%, -1.22% g·m-2 higher biomass yield (relative increases 0.80%, -3.29%, -1.22% g·m-2), respectively, with no significant effect of straw residue returned. (2) Compared with M0, M1 treatment decreased economic coefficient by 0.89% and 2.49%in 2004 and 2005 respectively, while it increased 2.68%;M2 increased by 0.98% and 4.10%in 2004 and 2006 respectively, but decreased 2.32% in 2005, as compared with M0. Economic coefficient decreased significantly with increasing N addition levels. (3) No significant M×N interaction was observed for economic coefficient.4. Effects of straw residue returned and N application rate on rice N uptake and utilization. (1) Compared with plants with straw removed (M0), M1 treatment increased shoot N content by 7.29%, 4.04% in 2004 and 2005 respectively, M2 treatment increased shoot N content by 5.21%, 2.73% in 2004 and 2005 respectively. N content increased significantly with increasing N addition levels. (2) Compared with plants with straw removed (M0), shoot N accumulation increased by 14.36%, 5.60% in 2004 for M1- and M2-treated plants, respectively, while it decreased by 0.06% and 0.23% in 2005 for M1- and M2-treated plants, respectively. N accumulation increased significantly with increasing N addition levels. (3) N use efficiency for biomass production (NUEp) showed negative responses to treatments with straw residue returned (P > 0.05), with the magnitude of reduction being larger for M1 than M2 treatment. NUEp decreased obviously with increasing N supply. N use efficiency for grain output (NUEg) and N harvest index (HNI) NUEp NUEg. (4) No significant M×N interaction was observed for N content, N accumulation, NUEp, NUEg and HNI.