| China is the largest rice producer in the world.Double cropping rice plays an important role in stabilizing rice planting area,increasing rice yield and ensuring food security in China.Although nitrogen application increased rice yield,long-term nitrogen application led to soil acidification.Straw returning can improve soil fertility and increase rice yield.However,straw decomposition is slow,especially in late rice season,affecting agricultural operations and even restricting rice growth.Previous studies have shown that accelerating straw decomposition can promote rice growth and increase rice yield.The application of lime in paddy field can promote straw decomposition due to its own alkaline,but there are few studies on the dynamics of straw decomposition.In addition,lime can significantly increase soil p H,improve soil microbial activity,promote organic mineralization,and increase the absorption of mineral nutrients by rice.However,previous studies mainly focused on the effect of lime on rice yield and soil quality,and few studies on rice quality.In particular,the effects of different limes on straw decomposition,yield and rice quality in double cropping rice system are still unclear.Therefore,through field experiments,we examined the effect of different lime materials(Ca O: calcium oxide;Ca(OH)2:calcium hydroxide;Ca CO3: calcium carbonate)application on yield and quality of double cropping rice under the condition of straw returning,with no lime as control(CK),in order to provide technical bases for yield increase and soil improvement in acid double cropping rice fields.The main research results are as follows :(1)The application of different lime materials had no significant effect on the yield and nitrogen uptake of early rice,but it was beneficial to improve the yield and nitrogen uptake of late rice.Compared with CK,the yield of late rice under Ca O,Ca(OH)2 and Ca CO3 treatments increased by 11.3 %,17.3 % and 17.6 %,respectively,and the nitrogen uptake increased by 16.6 %,17.1 % and 13.5 %.(2)Compared with the CK,except the application of Ca O had significant effect in chalky degree of early rice,different lime materials had no significant difference on other rice quality indexes of early rice.and had increased trend in Cd content in milled rice and brown rice of early and late rice,but the difference was not significant.which were 1.3-2.1 % and 6.1-6.3 % higher than those of CK.Application of lime significantly reduced amylose content of late rice by 4.7-4.8 %.Compared with CK,the application of Ca(OH)2 significantly decreased the the chalky rate of late rice,the application of Ca O and Ca CO3 increased the gel consistency,the application of Ca CO3 had significantly increased the breakdown value,but significantly decreased the setback value.(3)In winter fallow-early rice,different limes had significantly promoted straw decomposition at 138 days,169 days and 183 days after late rice straw returning,significantly promoted straw N release at 154 days and 183 days after straw returning,significantly promoted straw P release at 45 days after straw returning,and significantly promoted straw K release at 154 days and 183 days after straw returning.In late rice,different limes had significantly promoted straw decomposition rate at 43 days after early rice straw returning,promoted straw N release at 15 and 59 days after straw returning,and increased significant straw K release at 43 days after straw returning.Compared with the CK,the application of different limes had significantly increased the soil p H value after harvest of early and late rice,which increased by0.42-0.52 units and 0.41-0.57 units.The application of different limes had significantly increased the soil available N content at the early and late rice.Therefore,in acidic double cropping rice fields,the application of lime can significantly promote straw decomposition,increase late rice yield and improve rice quality while improving soil acidification,and the effects of different lime substances are consistent. |
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