Nitrogen transformation and acidity remediation in responses to water-fertilizer coupling management during straw decomposition at fixed temperature in yellow-paddy field

【Objectives】The impacts of soil water content, fertilization incorporated with addition of decay-facilitating microbial incolua on the N transformation and soil acidity remediation were investigated in low yield acidified yellow-paddy soil in double rice cropping area, central China. 【Methods】An incubation experiment involved by decay-facilitating microorganisms was respectively performed at 15℃ and 35℃ in laboratory for 105 days to evaluate impacts of soil water content 40% and 100% of water holding capacity (WHC) and N fertilizer (urea and manure). The soil inorganic nitrate (NO-3-N), ammonium (NH+4-N)), total dissolved nitrogen (TDN) and changes of pH were monitored periodically. 【Results】Data showed that water content and N fertilizer exhibited similar effects on N transformation and pH variance when soils were incubated by two kinds of temperatures, 35℃ and 15℃, and ammonium contents in soils were orderly classified into four levels by WHC40%+U WHC40%+M WHC100%+U WHC100%+M across the entire incubation period (P0.01) regardless of N fertilizer, but the contents of nitrate and TDN in treatments were all in orders of WHC100%+U WHC100%+M WHC40%+U WHC40%+M. The contents of nitrate and TDN reatments under WHC100% were increased significantly comparing with those under WHC40% (P0.05), not difference existed between fertilizer treatments. WHC40%+U showed higher net N mineralization than WHC100%+U when manure was applied, suggesting that microbial immobilization occurred in soils. Additionally, net nitrification in WHC100%+U was higher than that in WHC100%+M, but treatments incubated under WHC40% show slight nitrification; pH values are elevated in nearly all the treatments following a specific trend of WHC40%+M WHC40%+U WHC100%+M WHC100%+U, with net pH variation of +0.35, +0.51, -0.61 and +0.15, respectively. Obviously, although WHC100%+U leads to great increase in pH at initial stage, but decrease the pH by 0.61 at the end of incubation. Higher temperature, water content and urea application should be recommended as an effective field management practice for satisfactory N mineralization and pH elevation. Soil microorganisms have an adaptation to temperature for N mineralization, the magnitude of C- and N- mineralization mainly depend on the availability of soil water and N resources. Manure is an applicable choice despite of supplying less N of various forms and weak affecting in pH fluctuations. 【Conclusions】An integrative manage practice in maintaining capacity of soil water content and increasing the efficiency of N fertilizer should be an effective pathway during the process of returning straws from early rice and late rice to field at the low yield paddy soils in central China.