Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheatstraw return

Dry direct-seeded rice(DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient,relatively cheap,and environmentally friendly.However,this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment.To address this problem,we performed field experiments to determine the rice yield at five seedling density levels(B1,B2,B3,B4,and B5=100,190,280,370,and 460 seedlings m-2,respectively) and clarify the physiological basis of yield formation.We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018.The proportion of main stem panicle increased with increasing seedling density.There was a parabolic relationship between yield and seedling density,and the maximum yield(9.34-9.47 t ha-1) was obtained under B3.The maximum yield was associated with a higher total spikelet number m-2 and greater biomass accumulation from heading to maturity.The higher total spikelet number m-2 under B3 was attributed to an increase in panicle number m-2 compared with B1 and B2.Although the panicle numbers also increased under B4 and B5,these increases were insufficient to compensate for the reduced spikelet numbers per panicle.Lower biomass,smaller leaf area,and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5.The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m-2 of land,crop growth rate,net assimilation rate,and leaf area index.Furthermore,the B3 rice population was marked by a higher grain–leaf ratio,as well as a lower export ratio and transport ratio of biomass per stem-sheath.A quadratic function predicted that 260-290 seedlings m-2 is the optimum seedling density for achieving maximum yield.Together,these results suggested that appropriately increasing the seedling density,and thereby increasing the proportion of panicles formed by the main stem,is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.

Heavy soil drying during mid-to-late grain filling stage of the main crop to reduce yield loss of the ratoon crop in a mechanized rice ratooning system

Yield loss(Y_(Loss)) in the ratoon crop due to crushing damage to left stubble from mechanical harvesting of the main crop is a constraint for wide adoption of mechanized rice ratooning technology.Soil drying before the harvest of the main crop has been proposed to overcome this problem.The objective of this study was to determine the effect of soil drying during the mid-to-late grain filling stage of the main crop on grain yield of the ratoon crop in a mechanized rice ratooning system.Field experiments were conducted to compare Y_(Loss) between light(LD) and heavy(HD) soil drying treatments in Hubei province,central China in 2017 and 2018.Y_(Loss) was calculated as the percentage of yield reduction in the ratoon crop with the main crop harvested mechanically,relative to the grain yield of the ratoon crop with the main crop harvested manually.In comparison with LD,soil hardness was increased by 42.8%-84.7% in HD at the 5-20 cm soil depth at maturity of the main crop.Soil hardness at 5 and 10 cm depths reached respectively 4.05 and 7.07 kg cm^(-2) in HD.Soil drying treatment did not significantly affect the grain yield of the main crop.Under mechanical harvesting of the main crop,HD increased the grain yield of the ratoon crop by 9.4% relative to LD.Consequently,Y_(Loss) was only 3.4% in HD,in contrast to 16.3% in LD.The differences in grain yield and Y_(Loos) between the two soil drying treatments were explained mainly by panicles m^(-2),which was increased significantly by HD in the track zone of the ratoon crop compared with LD.These results suggest that heavy soil drying practice during the mid-to-late grain filling stage of the main crop is effective for reducing Y_(Loss) of the ratoon crop in a mechanized rice ratooning system.

Effects of different mechanical direct seeding methods on grain yield and lodging resistance of early indica rice in South China

Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China.Dry direct seeding(DDS)has been widely used for single-season rice planting establishment.However,few studies have examined the performance of early-season indica rice under mechanical dry direct seeding.A two-year field experiment was conducted with two indica rice cultivars(i.e.,Zhongjiazao 17 and Zhuliangyou 819)to study lodging characteristics and grain yield formation under DDS,flooded direct seeding(FDS)and wet direct seeding(WDS)patterns.The results showed that the annual grain yield in DDS was higher by 14.42–26.34%for cultivar ZLY819 and 6.64–24.58%for cultivar ZJZ17 than in WDS and FDS,respectively,and these increases were mainly attributed to the improvement of the panicles.The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars,and increased total dry weight and crop growth rate.Meanwhile,shorter basal internodes,better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS.In particular,DDS improved the stem lodging resistance.Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.

A Preliminary Study of the Key Technologies in Rice Seed Production

To study the production technology of rice seeds,with Lianjing 7 as test material,this paper explores the effects of the key rice seed production,processing and storage technologies( such as nitrogen fertilizer application and management,weeding mode in seed breeding field,temperature control of mechanical drying and water control on seed storage) on the quality of rice seeds. The results show that the optimal application proportion of tillering stage dressing and earing fertilizer is 8: 2,followed by 7 : 3; the best time of weeding is booting stage,with the highest purity; the effect of drying and germination rate is best when the temperature is controlled at 44℃ in mechanical drying process; the seed storage quality and storage costs can be guaranteed when the water content of rice seed is controlled at 18%.