| Rice (Oriza sativa L.) is one of the major food crops, high and stable yields of rice grains play a very crucial role for food security. The contribution rate of chemical fertilizer application in the increase of food production is about 50% in the world and more than 40% in China. The optimum application amount of nitrogen internationally recognized is 225 kg/ha. Nitrogen use efficiency in developed countries ranged from 46% to 68%. Nitrogen dose applied for single season crops in China excessed 250 kg/ha, but nitrogen use efficiency ranged from 30% to 35%, lower than the average in the world. Excessive supply of chemical fertilizer has become one of the most prominent environmental problems. Recycling of nutrients in organic manure can partially replace chemical fertilizer, and also has important practical significance to establish the environment-friendly fertilization system. This paper studied on the effects of integrated fertilization with organic manure and chemical nitrogen fertilizer on nitrogen transformation in soils and its relation to ammonia volatilization nitrogen losses under the lab conditions, as well as on the growth and nitrogen use efficiency of early and late rice with rice-rice cropping system under field conditions. The main results were as follows:1. Two simulation experiments using paddy soils were conducted with four treatments such as no fertilization (CK), urea nitrogen treatment (T1),20% organic fertilizer nitrogen+80% urea nitrogen (T2),20% organic fertilizer nitrogen +64% urea nitrogen (T3). The results showed that water-soluble total nitrogen (TN), water-soluble NH4+-N, KCl-extractable NH4+-N, exchangeable NH4+ -N concentrations in paddy soils of T2 and T3 treatments were evidently or significantly (P<0.05) lower than those of urea nitrogen treatment (T1). Water-soluble TN, water-soluble NH4+-N, KCl-extractable NH4+ -N and exchangeable NH4+ -N concentrations in paddy soils were significantly (P<0.01) positively correlated to each other. Accumulated nitrogen losses of ammonia volatilization of T2 and T3 treatments were significantly (P<0.01) lower than that of T1 treatment. Accumulated nitrogen losses of ammonia volatilization of T3 treatment was significantly (P<0.01) lower than that of T2 treatment, indicating that application of chemical nitrogen fertilizer combined with organic manure can reduce ammonia volatilization loss in paddy soils. The peak value of ammonia volatilization rate was significantly (P<0.01) linear correlated to soil water-soluble NH4+-N and exchangeable NH4+-N concentrations with the regression coefficients as 0.0233 and 0.0062 in the soil from Jiangxi and as 0.0133 and 0.0003 in the soil from Hubei. The regression coefficients of exchangeable NH4+-N was significantly less than that of water-soluble NH4+-N, implying that nitrogen existent as exchangeable NH4+-N can reduce ammonia volatilization rate at the same nitrogen dose. The appropriate technical measures for increasing soil CEC and nutrient preserving capability should be recommended.2. Two simulation experiments using upland soils were conducted with four treatments such as no fertilization (CK), urea nitrogen treatment (T1),20% organic fertilizer nitrogen+80% urea nitrogen (T2),20% organic fertilizer nitrogen +64% urea nitrogen (T3). The results showed that water-soluble TN, water-soluble NO3-N concentrations in paddy soils of T2 and T3 treatments were significantly (P<0.05) lower than T1 treatment (except the second day sampling). Water-soluble TN concentration in paddy soils was significantly (P<0.01) positively correlated to water-soluble NO3-N concentration, and water-soluble NO3-N concentration was significantly (P<0.01) negatively correlated to water-soluble NH4+-N, KCl-extractable NH4+-N and exchangeable NH4+-N concentrations. Accumulated nitrogen losses of ammonia volatilization of T2 and T3 treatments were significantly (P<0.01) lower than that of T1 treatment. Accumulated nitrogen losses of ammonia volatilization of T3 treatment was significantly (P<0.01) lower than that of T2 treatment, indicating that application of chemical nitrogen fertilizer combined with organic manure can reduce ammonia volatilization loss in upland soils. The peak value of ammonia volatilization rate was significantly (P<0.01) linear correlated to soil water-soluble NH4+-N and exchangeable NH4+-N concentrations with the regression coefficients as 0.0207 and 0.0108 in the moisture soil and as 0.0045 and 0.0017 in the black soil. The regression coefficients of exchangeable NH4+-N was significantly less than that of water-soluble NH4+-N, implying that nitrogen existent as exchangeable NH4+-N can reduce ammonia volatilization rate at the same nitrogen dose. It is practically significant to enrich the soil fertility.3. A field experiment with rice-rice rotation was conducted with six treatments such as no fertilization (CK), phosphorus and potassium treatment (PK), the farmer conventional fertilization (FP(N)), single manure (M(20%N)),20% organic fertilizer+80% chemical fertilizer-high yield and high efficiency fertilization treatment (CM(N)),20% organic fertilizer +64% chemical fertilizer-nitrogen efficiency treatment (CM(-N).In early rice growing season, the results showed that soil water-soluble NO3-N, water-soluble NH4+-N, water-soluble TN, KCl-extractable NH4+-N, exchangeable NH4+-N and alkali-hydrolyzable N concentrations of CM(N) treatment were significantly (P<0.05) higher than those of CK, PK, M(20%N)treatments at beginning of tillering stage. Soil KCl-extractable NH4+-N, exchangeable NH4+-N and alkali-hydrolyzable N concentrations of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK, M(20%N)treatments at maximum tillering stage. Soil water-soluble TN was significantly (P<0.05) positively correlated to water-soluble NO3 at all growing stages, and alkali-hydrolyzable N was significantly (P<0.05) positively correlated to KCl-extractable NH4+-N and exchangeable NH4+-N at tillering stage and harvest stage. Soil urease activities of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK, M(20%N) treatments at regeneration and harvest stage, and soil sucrase activity of CM(N) treatment was significantly (P<0.05) higher than those of CK, PK treatments at maximum tillering stage.Early rice grain yields and total shoot biomass of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK M(20%N) treatments. Rice grain yields and total shoot biomass of CM(N), CM(-N) treatments were similar to that of FP(N) treatment. Nitrogen agronomic efficiency of CM(N) and CM(-N) treatments were 15.08 kg/kg and 18.65 kg/kg in order, which were significantly (P<0.05) higher than that of FP(N) treatment. Apparent nitrogen use efficiency of CM(N) and CM(-N) treatments were 35.18% and 38.96% in order, which were evidently or significantly (P<0.05) higher than that of FP(N) treatment. It was found that integrated fertilization with organic manure and chemical fertilizers at the same nitrogen dose or reducing nitrogen dose could produce similar grain yield, and improve nitrogen use efficiency as well.In late rice growing season, the results showed that soil water-soluble NO3-N, water-soluble TN, and alkali-hydrolyzable N concentrations of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK treatments at tillering stage. Soil KCl-extractable NH4+-N and exchangeable NH4+-N concentrations of CM(N), CM(-N) treatments were significantly (P<0.05) higher than that of FP(N) treatment at maximum tillering stage. Soil water-soluble TN was significantly (P<0.05) positively correlated to water-soluble N03N at all growing stages, and alkali-hydrolyzable N was significantly (P<0.05) positively correlated to water-soluble TN, water-soluble NO3-N, KCl-extractable NH4+-N and exchangeable NH4+-N at tillering stage and harvest stage. Soil urease activities of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than that of CK treatment at maximum tillering stage, and soil sucrase activities of FP(N), CM(N) treatments were significantly (P<0.05) higher than that of CK treatment at maximum tillering and harvest stage.Late rice grain yields, total shoot biomass and nitrogen amounts accumulated in shoot of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK M(20%N) treatments. Rice grain yields, total shoot biomass and nitrogen amounts accumulated in shoots of CM(-N) treatment were significantly (P<0.05) lower than those of FP(N) treatment. Nitrogen agronomic efficiency of CM(N) and CM(-N) treatments were 16.53 kg/kg and 18.82 kg/kg in order, which were significantly (P<0.05) higher than that of FP(N) treatment. Apparent nitrogen use efficiency CM(N) and CM(-N) treatments were 48.07% and 48.41% in order, which were significantly (P<0.05) higher than that of FP(N) treatment. It was found that integrated fertilization with organic manure and chemical fertilizers at the same nitrogen dose could produce similar grain yield and total shoot biomass, accumulate nitrogen amounts in shoots, and improve both of nitrogen agronomic efficiency and apparent nitrogen use efficiency.For the rice-rice cropping rotation, the results showed that two-season rice grain yields, and nitrogen amounts accumulated in shoots of FP(N), CM(N), CM(-N) treatments were significantly (P<0.05) higher than those of CK, PK M(20%N) treatments. Two-season rice grain yields of CM(N), CM(-N) treatments were significantly (P<0.05) lower than that of FP(N) treatment, and nitrogen amounts accumulated in shoots of CM(-N) treatment was significantly (P<0.05) lower than those of FP(N), CM(N) treatments. Nitrogen agronomic efficiency of CM(N) and CM(-N) treatments were 15.86 kg/kg and 18.74 kg/kg in order, which were significantly (P<0.05) higher than that of FP(N) treatment, and nitrogen agronomic efficiency of CM(-N) treatment was significantly (P<0.05) higher than that of CM(N) treatment. Apparent nitrogen use efficiency of CM(N) and CM(-N) treatments were 42.16% and 44.07% in order, which were significantly (P<0.05) higher than that of FP(N) treatment, and apparent nitrogen use efficiency of CM(N) treatment was similar to that of CM(-N) treatment. It was found that integrated fertilization with organic manure and chemical fertilizers at the same nitrogen dose or reducing nitrogen dose could improve nitrogen use efficiency, but the treatment with reducing 20% chemical nitrogen fertilizer based on CM(N) treatment was not conducive to maintain sustainable high-yield of rice grain. |
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