Study On Paddy Soil Fertility And Rice Nutrient Characteristics Under Continuous Non-flooded Plastic Film Mulching

Long-term experiment was conducted to study the effects of continuous plastic film mulchingunder non-flooding condition on paddy soil fertility properties and nutrition uptake of rice, whichstarted in 2001 at Duntou town of Lanxi city (basin area) and Dinqiao town of Haining city (plainarea), in Zhejiang Province, China, with one rice crop annually. The experiment was a randomizedsplit block design with three replications. At Duntou site, the main treatments included: nitrogendoses with 0, 45, 90, 135, 180 kg/hm² under non-flooded plastic film mulching condition (PM), noplastic film mulching and no flooding with 135 kg/hm² nitrogen (UM), and traditional floodingmanagement with 135 kg/hm² nitrogen (TF), subplots include rice straw incorporation or not. AtDinqiao site, the main treatments included: nitrogen doses with 0, 45, 90, 135, 180 kg/hm² undernon-flooded plastic film mulching condition, subplots include rice straw incorporation or not, andCK were UM with 135 kg/hm² nitrogen and TF with 135 kg/hm² nitrogen. Soil samples werecollected and analyzed for soil physical, chemical and biological properties, as well as thenutrition uptake characteristic of rice after six years's continuous planting. The results were asfollows:Continuous PM regime promoted the number of soil microaggregates (less than 5 mm) andimproved soil pH value slightly compared to TF treatment, whereas compared to UM treatment,the amount of more than 5 mm soil aggregation was decreased and that of 2 - 5 mm soilaggregation was increased, but soil pH value was decreased slightly.Continuous PM regime decreased soil organic matter content. After six years, the soil organicmatter content in PM decreased by 36.7% at Duntou site and by 54.1% at Dingqiao site comparedto the initial experiment soils, respectively. Compared to TF, PM decreased soil hydrolysis N andavailable K by 5.3% - 14.8% and 13.2% - 20.8%, respectively, during the growing stage of rice(before transplanting, jointing stage, grain-filling stage and maturing stage) at Duntou site,however, soil available P was increased by 5.1% - 21.6%, as well as soil available Si by 2.5% -9.1%. Compared to UM, PM decreased soil hydrolysis N, available P and available K by 2.4% -11.1%, 7.0% - 12.7% and 1.6% - 25.9%, respectively, however, available Si content had nosignificant difference between PM and UM. At Dingqiao site, compared to TF, PM reducedsignificantly soil hydrolysis N by 8.7% - 25.1%, and improved available P by 23.4% - 114.4%,whereas the dynamic of available K content was inconsistent in different growing stages of rice,and soil available Si was decreased significantly by 11.7% and 7.6% at grain-filling stage andmaturing stage, respectively. Compared to UM, PM reduced soil hydrolysis N significantly atbefore transplanting and jointing stage, available P was decreased significantly by 13.7% - 47.3%,as well as available K and available Si by 5.0% - 22.4% and 1.9% - 7.6%, respectively. Soilorganic matter content was affected by nitrogen fertilizer application. Compared with CK (N0kg·hm^-2), soil organic matter content was increased significantly by 11.8% and 11.3% after N 135kg·hm^-2 and N 180 kg·hm^-2 application at Duntou site. With the improvement of nitrogen dose, soilhydrolysis N was enhanced significantly by 7.7%, 12.9%, 15.3% and 22.5% at Duntou site and by 12.2%, 12.7%, 23.1% and 29.2% at Dingqiao site after 45 kg/hm², 90 kg/hm², 135 kg/hm² and 180kg/hm² nitrogen fertilizer application, respectively. The more the nitrogen fertilizer dose was, thehigher soil hydrolysis N was. Soil available P was significantly improved by 6.6% - 45.1% andavailable K content wasn't influenced by nitrogen fertilizer application at Duntou site, whereasavailaNe P and available K were reduced significantly by 27.1% - 59.8% and 6.3% - 19.6%,respectively, after nitrogen fertilizer application at Dinqiao site.Continuous non-flooded plastic film mulching had no remarkable effect on soil total Fe, Mn,Cu, Zn content compared to TF, but soil total Fe was improved significantly by 11.8% and 7.7% atmaturing stage in 2005 and at jointing stage in 2006 compared to UM, and total Mn content wasenhanced by 17.4% at maturing stage in 2005, total Cu and total Zn content had a slight butstatistically insignificant change. Soil available Fe and available Mn content were decreasedremarkably by 11.4% - 15.1% and 10.8% - 33.5% during the whole growth stage of rice,respectively, compared to TF, and available Cu was improved by 1.6% - 15.0%, and available Zncontent was inconsistent trend during the growth stage of rice. Compared with UM, soil availableFe, available Mn and available Cu content were enhanced under PM regime, but there wasinconsistent trend on available Zn content in 2005 and 2006.Compared with TF, PM had no remarkable effect on catalase activity, however, ureaseactivity under PM treatment was significantly improved by 28.7% and 45.6% at grain-filling stageand maturing stage, respectively. And sucrase activity was also markably enhanced by 14.2% - 3times during the whole growth stage, and soil alkaline phosphatase activity under PM treatmentsignificantly increased 60.0%, 51.1% and 43.8% at maturing stage in 2005 and 2006 and atgrain-filling stage in 2006, respectively. Compare to UM, PM regime had no markable effect oncatalase activity, whereas, PM significantly decreased urease activity by 14.1% - 45.6% during thegrowth of rice, and sucrase was markably enhanced by 95.3% and 57.7% at jointing stage andgrain-filling stage in 2006, respectively, and soil alkaline phosphatase activity under PM treatmentsignificantly increased 26.3%, 17.5% and 31.3% at maturing stage in 2005 and 2006 and atgrain-filling stage in 2006. The results in two years showed that soil catalase, urease, sucrase andalkaline phosphatase activities were improved after nitrogen fertilizer application, but the highestwas the treatment of N135 kg/hm² application.PM regime affected soil microbial biomass content. Compared to TF, microbial biomasscarbon was significantly decreased by 12.2% and 8.2% at before transplanting and maturing stageunder PM treatment, respectively. PM declined microbial biomass nitrogen at before transplanting,but significantly increased by 45.0% and 35.4% at jointing stage and grain-filling stage,respectively. Microbial biomass phosphorus was significantly increased by 8.7% - 3 times duringthe growth stage of rice. Compared with UM, the increased trend of soil microbial biomass C, Nand P was found under PM treatment. Soil microbial biomass C, N and P were improved bynitrogen application, but the highest microbial biomass C, N and P in different N dose were thetreatment of N135 kg/hm² application, which was 243.2 mg/kg, 37.5 mg/kg and 15.0 mg/kg,respectively. Non-flooded plastic film mulching changed soil environment, so soil bacterial communitydiversity was changed. The result of community level physiological profiles (CLPP) showed thataverage well color development (AWCD) generally followed at the sigmoid pattern withincubation time, and AWCD under PM regime was significantly higher than that of TF regime atjointing stage and grain-filling stage after 72 h incubation, and there was statistically significantdifference on PC1 between PM and TF (P＜0.05^*), and Shannon richness and evenness under PMregime were remarkably higher than those of TF regime. These results suggested that continuousPM regime in paddy fields had a diverse culturable bacterical population compared with TF.Moreover, AWCD, Shannon richness and evenness under PM regime were markedly higher thanthose of UM regime at jointing stage, and there was significant difference on PCl between PMand UM (P＜0.05^*), but no remarkable difference was found between PM and UM treatments atgrain-filling stage. These results showed that PM treatment stimulated the development of adiverse bacterial community to a larger extent than UM treatment at jointing stage. Denaturinggradient gel electrophoresis (DGGE) showed that PM enhanced significantly total bands onDGGE fingerprint profiles compared with TF and UM, and similarity dendrograms by the imageanalysis of DGGE profiles showed that the communities of PM and UM regimes were moresimilar to each other than they were to the TF regime.Straw incorporation was important to maintain paddy soil fertility under continuous PMregime. Rice straw incorporation increased soil organic matter content, hydrolysis N content,available P content and available K content by 6.25%, 9.9%, 12.3% and 61.5% at Duntou stie andby 5.2%, 15.3%, 17.8% and 12.9% at Dinqiao site, respectivity. Especially, compared to no strawincorporation under TF, soil organic matter and hydrolysis N content had no significant differenceunder PM and straw incorporation at two sites, but available P and available K were increasedsignificantly by 33.9% and 48.6% at Duntou site and 44.1% and 14.5% at Dingqiao site. Andcatalase, urease, sucrase and alkaline phosphatase activity were improved by 12.3%, 35.3%,24.1% and 25.0% at maturing stage in 2005 and 11.8%, 28.3%, 11.6% and 50.0% in 2006 underrice straw incorporation, and soil microbial biomass C, N, P were increased.Continuous PM regime changed paddy soil fertility, so grain yield and nutrient uptake of ricewere affected. From 2001 to 2003, grain yield increased gradually, the hightest was in 2003, andthe grain yield decreased gradually from 2004 to 2006, but increased slightly in 2007. In 2006,kernel number and seed setting rate of rice under PM were decreased by 6.6% and 2.5%,respectively, so the yield of grain of the PM regime lower than the TF regime, decreased by 5.0%,however, N content in shoot of rice under PM regime was increased by 6.0%, and P content wasdeclined by 9.6%, and K content had no significant difference at maturing stage. Because of theimprovement of the effective panicle number per plant and kernel number, grain yield under PMtreatment was remarkably higher than that of UM treatment, increased by 6.1%, and N, P and Kcontents in shoot of rice under PM regime were increased by 24.8%, 18.3% and 4.3% at maturingstage, respectively. Compared with CK (NO kg/hm²), N, P, K content in shoot of rice under PMregime were increased after N fertilizer application at maturing stage, and the highest content of N, P, K in different N dose was the treatment of N180 kg/hm² application, which were 1.286g/plant, 0.227 g/plant and 1.810 g/plant, respectively. With the improvement of the N dose, total N,P and K content in shoot of rice enhanced gradually, but no signicant difference was foundbetween N135 kg/hm² and N180 kg/hm² application. Average effective panicle number per plant,kernel number, seed setting rate and 1000-grain weight under PM management were enhanced byN application, so the grain yield was improved, and the highest yield was 7104 kg/hm² underN135 kg·hm² application and the incorporation of rice straw. The positive correlated relationshipwas found between grain yield (Y) and N dose (X), and the fitting parabola equations under ricestraw incorporation and no rice straw incroporation were as follows: (?) = 5390.2 + 20.216 X -0.0613 X² (R² = 0.9869^*) and (?) = 5212.2 + 15.287 X- 0.0306 X²(R² = 0.9869^*). In addition,compared to CK (NO kg/hm²), N application increased N harvest index and fertilizer-N-recoveryefficiency, but agronomic-N-use efficiency was decreased. Among these N dose, the highest Nharvest index and fertilizer-N-recovery efficiency were the N135 kg·hm² application and ricestraw incorporation, which were 0.626 and 49.6%, respectively, and agronomic-N-use efficiencywas 12.6 kg grain/kg. Rice straw incropation could promote the nutrient content in shoot of rice,grain yield and N use efficiency under PM treatment.PM affected Fe, Mn, Cu, Zn content in shoot of rice. Compared with TF, Fe content in thestem, panicle axis, hull, brown rice and total Fe content in shoot under PM regime were decreasedsignificantly by 9.1%, 29.1%, 46.2%, 25.0% and 9.5%, respectively. And Mn content in stem, hull,brown rice and total Mn content in shoot also decreased remarkably by 6.5%, 74.2%, 32.9% and10.3%, respectively. However, Cu content in stem and total Cu content in shoot of rice under PMtreatment enhanced by 100.1% and 15.0%, Cu content in panicle axis and brown rice decreased by25.8% and 20.8%. Zn content in hull and brown rice were decreased by 59.5% and 7.9%, but totalZn content in shoot had no significant difference between PM and UM. Compared to UM, Fe, Mn,Cu, Zn content in different organ of rice under PM had different changes, whereas total Fe, Mn,Cu, Zn content in shoot were increased by 28.0%, 35.0%, 35.2% and 15.8%, there was noremarkable difference in brown rice between PM and UM.In conclusion, paddy soil fertility under continuous PM regime was decreased, so we mustpay more attention to apply fertilizer rationally, such as N fertilizer, potassium fertilizer and ricestraw incorporation application for sustainable ecosystem, at the same time, the micronutrientfertilizer was important for the rice growth under PM management to improve grain yield and thequality.