Effects Of Straw Incorporation Coupled Nitrogen Levels On Biochemical Properties Of Paddy Soil And Growth Characteristics Of Rice

Higher nitrogen (N) application rate and large number of straw residual are not beneficial to thesustainable development of rice (Oryza sativa L.) production. Therefore, it is worth studying effects ofstraw incorporation coupled with nitrogen application rates on biochemical properties in paddy soil andgrowth characteristics in rice. Four straw incorporation rates coupled with four N application rates wereconducted in the field experiment from2012to2013. Rice cultivar used in this trial was hybrid indicarice, Zhongzheyou1. Straw incorporation rate used in this trial was0(S0),4000kg ha-1(S4),6000kgha-1(S6),8000kg ha-1(S8), respectively. N application rate used in this trial was0(N0),90kg ha-1(N90),180kg ha-1(N180),270kg ha-1(N270), respectively. Soil organic matter and quality, soilenzyme activities, soil microbial biomass carbon, rice tillers variations, photosynthetic characteristics ofrice flag leaf, dry matter accumulation, and rice nitrogen uptake were studied to compare the effects ofstraw incorporation coupled with nitrogen application rates on soil fertility and rice grain yield. Therelationship between biochemical properties in paddy soil and growth characteristics in rice was alsoinvestigated. Main results showed as follows:After two-year filed experiment, soil humus became more active, soil enzyme activities, microbialbiomass, soil N, P, K content were increased by straw incorporated with N fertilizer. Soil dissolvedorganic carbon and organic matter in straw incorporated with N treatments were significantly increasedby41.96~115.77mg kg-1and20.26%~33.51%, respectively. The highest content of soil dissolvedorganic carbon and organic matter were observed in N180S6. Compared with CK (N0S0), strawincorporated with N decreased HA/FA (Humic/Fulvic), and N180S6obviously decreased the HA/FAcomparing to CK. To compare with CK, straw incorporated with N enhanced soil enzyme activitiesrelating to straw decomposition. Compared with CK, the activity of urease, invertase, celluase andβ-glucosidase in N180S6was increased by22.11%,69.55%,41.07%, and52.06%, respectively. Strawincorporated with N effectively weakened the inhibition of soil microorganism induced by fertilizerapplication, and greatly increased soil microbial biomass carbon. In the same N application rate, soilorganic matter quality, enzyme activity, and microbial biomass were improved with the increase ofstraw incorporation rates, while these biochemical properties were declined after straw incorporationrate was higher than S6. After two-year experiment, soil available nitrogen, phosphorus and potassiumcontent in straw incorporated with N treatments were increased by0.48,18.58and18.21mg kg-1,respectively. The total nitrogen, phosphorus and potassium content were increased by8.82,16.14and10.81mg kg-1, respectively. Compared to N0S0, available and total phosphorus, potassium contentswere increased significantly in straw incorporated with N treatments.After two years of field experiment, the phenomenon of “nitrogen competition” between ricegrowth and straw decomposition was effectively alleviated in straw incorporated with N treatments.Meanwhile, straw incorporated with N maintained high photosynthetic rate of rice flag leaf after ricefull heading stage, increased rice tillers number, improved rice dry matter accumulation andtransformation. To compare with CK, rice yield of N application, straw incorporation and its interactiontreatments was increased by2.57%~23.51%, and grain yield in N180S6treatment was significantlyhigher than CK. Variance analysis showed that N application, straw incorporation and its interactionsignificantly affected rice yield formation. Compared with N0S0, straw incorporated with N increasedtotal plant nitrogen absorption significantly, N270S6showed the highest values. In the same nitrogen application rate, rice plant nitrogen absorption was enhanced with the increase of straw incorporationrates, while nitrogen contents was declined after straw incorporation rate was higher than S6. Nitrogenphysiological efficiencies and physical productive efficiencies in straw incorporated with N treatmentswere significantly improved comparing to CK, indicating that straw incorporated with N application notonly increased dry matter accumulation but also improved nitrogen using efficiency.