| Field experiments were conducted from 2013 to 2015 under field conditions.The first experiment was conducted at Xinghua(33.10°N,119.96°E)of Lixiahe region,Yangzhou(32.30°N,119.25°E)of Yanjiang region,Changshu(31.69°N,120.68°E)of Taihu Lake region,and Ningbo(29.45°N,121.31°E)of Ningshao Plain in 2013 and 2014,with 15 LMYS as the materials and japonica(CK-J)and indica(CK-I)varieties as the check.The suitable growing zone of LMYS was defined based on their maturity dates and grain yield performance.The second experiment was conducted at Ningbo to identify physio-morphological traits underlying high yield of LMYS.The physio-morphological traits were mainly focused on grain yield and its components,plant-type traits,grain filling characteristics,nitrogen(N),phosphorus(P),and potassium(K)accumulation and translocation,and dry matter accumulation characteristics after heading.Besides,suitable application rate of K and silicon(Si)were also explored in this study.This study provided important implications for development of LYMS in the lower reaches of Yangtze River and identifying physio-morphological traits underlying high yield of LYMS.The main results were followings:(1)The maturity dates of the 15 LMYS were later than the secure maturity date at Xinghua and 6,14,and 15 LMYS were mature before the secure maturity date at Yangzhou,Changshu,and Ningbo,respectively.One variety was identified as high-yielding variety among LMYS(HYYS)at Yangzhou,8 HYYS in 2013 and 9 HYYS in 2014 at Changshu,9 HYYS at Ningbo.HYYS here refers to the variety among LMYS that was mature before the secure maturity date and had at least 8%higher grain yield than both CK-J and CK-I at each experimental site.High yield of HYYS was mainly attributed to larger sink size due to more spikelets per panicle.Significant positive correlations were recorded between duration from heading to maturity and grain yield,and also between whole growth period and grain yield.Comprehensive consideration about safe maturity date and yield performance of LMYS at each experimental site,Taihu Lake region(representative site Changshu)and Ningshao Plain(representative site Ningbo)were thought suitable growing zone for LMYS in the lower reaches of Yangtze River.The main factors underlying high yield of HYYS were larger sink size,longer duration from heading to maturity and whole growth period.(2)CK-I had the highest panicle length,followed by LMYS,and CK-J.LMYS showed higher grain density and number of spikelets in six parts in the panicle compared with CK-J and CK-I.The leaf length and width of upper three leaves of CK-I were the highest,followed by LMYS,and CK-J.LMYS showed lower leaf basic angle and dropping angle relative to CK-J and CK-I.The plant height,panicle height,and stalk height of CK-I were the highest,followed by LMYS,and CK-J.LMYS showed higher dry weight per stem,and dry weight per sheath when compared with the CK-J and CK-I.(3)LMYS showed higher N accumulation at jointing,heading,and maturity relative to CK-J and CK-I,as well as N accumulation from jointing to heading and from heading to maturity.There existed significantly(p<0.01)positive correlation between N accumulation from sowing to jointing,from jointing to heading,and from heading to maturity,and rice grain yield.CK-J showed the highest P accumulation at jointing,followed by CK-I,and LMYS.LMYS showed the highest P accumulation at heading and maturity among rice variety types,as well as P accumulation from jointing to heading and from heading to maturity.There existed a significantly(p<0.01)negative correlation between P accumulation from sowing to jointing and rice yield.There existed significantly(p<0.01 or p<0.05)positive correlation between P accumulation from jointing to heading and from heading to maturity and rice grain yield.LMYS showed higher K accumulation at jointing,heading,and maturity.LMYS showed higher K accumulation from heading to maturity compared with CK-J and CK-I.CK-I showed the highest NUEg,followed by CK-J,and LMYS in both years.LMYS showed higher KUEg relative to CK-J and CK-I.There existed a significantly(p<0.05)negative correlation between NUEg and rice grain yield,while a significantly(p<0.01)positive correlation between KUEg and rice grain yield was observed in our study.There existed a positive(p<0.01)correlation between N translocation from the stem from heading to maturity and rice grain yield,while a negative correlation between N and P translocation from the leaf from heading to maturity and rice grain yield was observed.Our study showed that LMYS showed higher N,P,and K accumulation relatie to CK-J and CK-I.LMYS showed lower NUEg,while higher KUEg.Stimulating N translocation from stem from heading to maturity,while not N or P translocation from the leaf from heading to maturity was beneficial for increasing rice grain yield.(4)For Yongyou 538,grain-filling processes of UP and MP were synchronous types,as well as US and MS,and LP and LS,but grain-filling processes of UP and MP,US and MS,LP and LS were asynchronous types.For Zhongzheyou 1 and Xiushui 09,grain-filling processes of UP,US and MP were synchronous types,while asynchronous types existed between UP,US,MP and LP,LS.Yongyou 538 showed more asynchronous in grain filling process compared with the check.The mean final weight of a kernel of the six parts in the panicle of Xiushui 09 was the highest,mean value of maximum grain-filling rate and mean grain-filling rate showed Zhongzheyou 1>Xiushui 09>Yongyou 538,while effective grain-filling period showed Yongyou 538>Xiushui 09>Zhongzheyou 1.The grain filling in panicle and panicle weight of Yongyou 538 were greatly increased due to its higher effective grain filling duration and more spikelets per panicle,although lower filling rate.(5)Dry matter accumulation of LMYS was 8.9 t ha-1,19.1%and 25.8%higher than that of CK-J and CK-I,respectively.Richards' equation was fit to simulate the relationship between dry matter weight and days after heading for three types of rice variety(R2>0.990).Rate of dry matter accumulation of three types of rice variety decreased after an even increase.Maximum rate of biomass accumulation and mean rate of biomass accumulation after heading of CK-I were the highest,followed by those of CK-J,and LMYS.Days to maximum rate of dry matter accumulation after heading of LMYS was at 43-44 d after anthesis,while those of CK-J and CK-I were both at 27-28 d after anthesis.Duration of gradual increase stage and dry matter accumulation in this stage were higher in LMYS than in the CK-J and CK-I,while mean rate of dry matter accumulation during gradual increase stage was higher in CK-I than in LMYS.The duration and dry matter accumulation during fast increase stage and slow increase stage of CK-J were the highest among three types of rice variety,while mean rate of dry matter accumulation during fast increase stage and slow increase stage of CK-I was the highest.Our results implied that greater dry matter accumulation mainly occurred in the gradual increase stage for LMYS,which was mainly attributed to the longer duration of this stage.(6)This study was conducted to determine the suitable Si application rate of LMYS in Ningbo zone with respect to the Si deficiency in soil.Using Yongyou 12 and Yongyou 15 as the material,effects of Si application rate on the grain yield and characteristics of yield formation of Yongyou 12 and Yongyou 15 were compared and studied.Grain yield of Yongyou 12 and Yongyou 15 were both increased firstly and then decreased with the Si application rate.The highest grain yield of Yongyou 12 and Yongyou 15 were both achieved at the Si application rate of 225 kg ha-1.Analysis on yield components showed that number of panicles of Yongyou 12 and Yongyou 15 were increased with the increased Si application rate,while 1000-grain weight and seed-setting rate were both decreased with the increased Si application rate.With the increased Si application rate,number of tillers and stems of Yongyou 12 and Yongyou 15 at jointing,heading,and maturity stage were both increased synchronously.Panicle rate of Yongyou 12 and Yongyou 15 were both increased firstly and then decreased with the Si application rate,with Si rate of 225 kg ha-1 the highest.With the increased Si application rate,dry matter weight and leaf area index at jointing,heading,and maturity stage were increased synchronously.As well as dry matter accumulation and leaf area duration from jointing to heading and from heading to maturity.With the increased Si application rate,leaf length and leaf width of the 1st leaf,2nd leaf,and 3rd leaf of Yongyou 12 and Yongyou 15 were increased synchronously,while leaf basic angle and dropping angle of the 1st leaf,2nd leaf,and 3 rd leaf of Yongyou 12 and Yongyou 15 were decreased synchronously.Moreover,compared with check(0 kg ha-1),Si application treatment significantly increased dry matter per stem,per sheath,and per length of stem.(7)In order to investigate proper K application rate and its effects on growth and grain yield for LMYS,a field experiment was conducted using Yongyou 12 and Yongyou 538 with five K application rate treatments of 0,75,150,225,and 300 kg ha-1.Results indicated that compared with check treatment(0 kg ha-1),K application treatment increased yield by 9.2%-14.0%for Yongyou 12,and 9.8%-15.0%for Yongyou 538.In both years,the highest grain yield of Yongyou 12 and Yongyou 538 was both achieved at K application rate of 225 kg ha-1.K application treatment significantly increased number of panicles and spikelets per panicle.With the increase of K application rate,leaf area index and plant dry matter weight at jointing,heading,and maturity stages,as well as leaf area duration and dry matter accumulation from jointing to heading,and leaf area duration from heading to maturity were increased synchronously.Dry matter accumulation of plant from heading to maturity increased firstly and decreased then with the increase of K application rate,and the highest dry matter accumulation was achieved at K application rate of 225 kg ha-1.Compared with check treatment(0 kg ha-1),K application treatment increased SPAD value,photosynthetic rate,and root blending rate from heading to maturity.Compared with check treatment(0 kg ha-1),K application treatment increased significantly N and K absorption at jointing,heading,and maturity stage.N and K accumulation from heading to maturity was increased firstly and decreased then with the increase of K application rate,and the highest N and K accumulation was achieved at K application rate of 225 kg ha-1.K partial productivity,internal nutrient efficiency in K,and K agronomy efficiency all decreased with the increase of K application rate.Our study showed that K application treatment increased obviously rice grain yield relative to check treatment(0 kg ha-1),and the highest grain yield was observed at K application rate of 225 kg ha-1.The increased grain yield by K application treatment was mainly attributed to increasing spikelets per panicle and panicle.K application treatment significantly increased dry matter and leaf area index at main growth stages,delayed leaf and root senescence after heading,and increased N and K accumulation at main growth stages. |
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