Effects Of Planting Patterns, Straw Application And Site-specific Nitrogen Management On Grain Yield And Quality Of Rice And Their Physiological Mechanism

Straw application, development of dry-cultivation and direct-seeding and increase in nitrogenfertilizer use efficiency are hot issues in agricultural research. This study investigated the effectsof planting patterns, wheat-residue application and site-specific nitrogen management (SSNM)on grain yield and quality of rice and their physiological mechanisms by using typical ricecultivars and conducting field experiments. The main results are as follows:1. Effects of wheat-residue application and SSNM on grain yield and qualityIn comparison with the wheat-residue removal treatment, the wheat-residue application (theresidue was incorporated into soil) treatment increased the grain yield, reduced panicles per area,and increased the spikelets per panicle, filled-grain percentages and 1000-grain weight, andimproved rice appearance and cooking qualities. In comparison with farmers' fertilizer-Npractice (FFP), SSNM increased grain yield, reduced the grain protein content, but improved ricecooking quality. In comparison with the transplanting rice, the direct-seeding reduced grain yield,milled rice rate, head milled rice rate and gel consistency, increased amylose content, degradedthe milling quality and cooking quality, and showed little change in the appearance quality. Thewheat-residue application plus SSNM treatments enhanced the maximum grain filling rate andmean grain filling rate, shortened the active grain filling period in both transplanting anddirect-seeding. Compared to the transplanting rice, direct-seeding rice increased the maximumgrain filling rate and mean grain filling rate, shortened the active grain filling period the timereaching the maximum grain filling rate, and reduced the final grain weight. The results indicatedthat wheat-residue application and SSNM could increase the yield and improve rice quality simultaneity. Whereas direct-seeding might reduce the yield and degrade the milling and cookingqualities, relative to the transplanting rice.2. Growth and development characteristic under wheat-residue application and SSNMIn comparison with those under the residue removal or FFP, the number of stems and tillers,leaf area index (LAI), chlorophyll content (SPAD value) and biomass accumulation were less orlower under the wheat-residue application or SSNM during the early growth period, but thedifferences between the treatments were small at heading and thereafter. Both the strawapplication and SSNM increased the percentage of productive tillers, ratio of total spikeletnumber to leaf area, photosynthetic rate of the flag leaves, root activities, the activities ofAdenosine triphosphate enzyme (ATPase) and nitrate reductase (NR). Under the same nitrogenmanagement and the same amount of straw application, the direct-seeding increased themaximum number of tillers, while reduced the percentage of productive tillers and the ratio oftotal spikelet number to leaf area, and degraded the population quality. The differences intemperature and humidity between the day and the night, biomass accumulation and LAI weresmaller or lower under the direct-seeding than under the transplanting. During the grain fillingperiod, the direct-seeding increased the amount of root bleedings, NR activities of roots andmalondialdehyde (MDA) content in leaves, whereas reduced photosynthetic rate and ATPaseactivity of leaves at the late stage. The results suggested that the straw application and SSNMplay an important role in harmonizing the relationship of source and sink, accelerating thetransport of photosynthetic assimilation to grains, and enhancing matter production efficiency.3. Absorption and utilization characteristics of nitrogen (N), phosphorus (P) andpotassium (K) in rice plants under wheat-residue application and SSNMUnder the same planting pattern, wheat-residue incorporation reduced N content and theaccumulation of N, P and K in plants at the early growth stage, while increased P and K contentsin plants during the whole growth period and the percentage and amount of assimilatestransported from vegetative organs to grains. The straw application treatment also increased thenitrogen utilizing efficiency and harvest index and biomass production efficiency of N, P and Kwhen compared with the straw removal treatment. Under the same amount of strawincorporation, the amount of N and P absorption in plants were lower under SSNM than FFP.There was no significant difference in the amount of K absorption between SSNM and FFP. SSNM increased transportation percentage of N, P, K from heading to maturity, harvest index ofP and the K efficiency of grain production. In comparison with those under the transplanting, N,P and K contents of plants under direct-seeding were higher during the early growth period,whereas lower during the late growth period. The direct-seeding rice showed higheraccumulation of N and P in vegetative tissues, lower accumulation in the spikelets, lowertransportation percentage of N and P, higher amount and transportation efficiency of K, andhigher biomass production efficiency and harvest index of P and K, relative to the transplantingrice.4. Effect of wheat-residue application on physical and chemical characters andenzymatic activities in soilThe peak value of decomposition of wheat-residue was found at the first month after ricetransplanting or sowing. The contents of organic acids were increased significantly atmid-tillering and panicle initiation stages. Activities of urase and hydrogen peroxidase wereenhanced initially and then decreased, and showed a peak value at 30 and 60 days after ricetransplanting, and were significantly different at different developmental stages. The activity ofalkaline phosphatase in soil showed two peaks. The value of pH declined significantly, while thecontents of organic acids were raised, under wheat-residue incorporation, and there was negativecorrelation between them. The straw application increased activities of urase, hydrogenperoxidase and alkaline phosphatase, organic matter content and respiration rate, while reducedion contents of Na⁺, Mg²⁺ and Ca²⁺ in soil. Increase and decrease in the enzymatic activities andion contents were associated with the decay degree of wheat-residue. Urase activity was higherunder FFP than SSNM. There was no significant difference in other measurements of soilbetween FFP and SSNM. Activities of urase and alkaline phosphatase were significantlycorrelated with organic matter content and contents of total N, P and K.Hydrogen peroxidaseactivity was significantly correlated with the total N content, but not significantly correlated withthe contents of total P and K in soil.5. Effect of dry-cultivation mulched with straw (DCMS) on the yield, growth andphysiology of riceThere was no significant difference in the grain yield between DCMS and moist-cultivation(MC), but the grain yield of DCMS was significantly higher than that of dry-cultivation mulched with film (DCMF) or that of bare cultivation (BC). The differences in the milling quality,appearance quality, and cooking and nutrient quality of rice were not significant between DCMSand MC. Grains from DCMF and BC had higher chalkiness, smaller gel consistency, whencompared with those from MC. Peak viscosity and breakdown values were reduced and setbackvalues of the starch profile of rice endosperm were increased under dry-cultivation, speciallyunder DCMEDCMS rice showed slower tillering before the critical stage of productive tillers and higherpercentage of productive tillers than MC and DCMF rice. Dry matter accumulation of shoot fromheading to maturity under DCMF was lower, when compared with that under MC, butsignificantly higher than that under DCMF or under BC. Remobilization of assimilates fromvegetative tissues to grains and harvest index were higher under DCMF than those under MC.Dry-cultivation exhibited higher chlorophyll content, photosynthesis rate, and activities ofsuperoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) during grain filling,especially at the late filling stage when compared with MC. MDA content in leaves underdry-cultivation was higher than that under MC. The root activity of dry-cultivation ricedecreased rapidly at late grain filling stage. Except MDA, above physiological traits showed theorder of MC＞DCMS＞DCMF＞BC,. The results suggest that grain yield is higher and ricequality better under DCMS than those under other two dry-cultivation patterns.6. Grain-filling characteristics and changes in hormonal contents in the grains underdry-cultivationCompared to MC rice, dry-cultivation rice had lighter grain weight, greater grain-filling rate,and earlier time to reach the maximum grain-filling rate and shorter active grain-filling period,which was more obvious for inferior grains than for superior ones. The contents ofindole-3-acetic acid (IAA), zeatin riboside (ZR) and abscisic acid (ABA) were higher in superiorgrains than in inferior ones at early grain-filling stage. The peak of IAA and ZR contentsappeared just before, and that of ABA content simultaneously with the maximum grain-fillingrate. The grains of dry-cultivation rice contained less IAA and ZR but more ABA than those ofMC rice at early and mid grain filling stages, and the differences were mainly in inferior grains.When 20×10^-5 mol/l IAA was applied to plants at the initial grain filling stage, IAA and ZR wereincreased and ABA was reduced in inferior grains, and active grain-filing period was prolonged and grain-filling rate decreased. The grain weight of dry-cultivation rice was increased and thatof MC rice decreased to a different degree by application of IAA. When 25×10^-6 mol/l ABA wasapplied, the contents of hormones in grains, active grain-filling period and grain-filling rate werereversed with those of application of IAA, and the grain weight in dry-cultivation rice wassignificantly reduced. The results suggest that shortened grain filling period and reduced grainweight in dry-cultivation rice are attributed to an increase in ABA or decreases in IAA and ZR inthe grains. Regulation of the ratio of ABA to IAA in grains would increase the grain weight indry-cultivated rice.