Field experiments were conducted to investigate the effect of potassium(K) fertilizer on cotton yield components and correlations between yield components and yield in 2007-2008 in Beijing at the Shangzhuang Experiment Station(40°08'N,116°10'E) of China Agricultural University,with 34 cotton conventional cultivars/hybrids as materials.The results indicated that K fertilizer increased lint yield significantly,especially in 2008,characterized by lower temperature during seedling and square periods and excessive precipitation during almost whole growing season.Among yield components,the boll numbers per plant was affected most by K fertilizer,then the boll weight,and the lint percent was influenced least.Partial correlation analysis and path analysis showed that the correlation between yield and lint percent under low K levels was closer than that under high K levels.However,the effect of K level on the correlations of yield with boll number and boll weight changed with years,indicating that efficient selection in breeding probably requires appropriate environment.Furthermore,path coefficient analysis indicated that indirect effects of yield components upon yield changed with years and K levels,suggesting complex mutual relationships among lint percentage,boll weight and boll numbers.

Field studies were conducted in 2004 and 2005 at Wuqiao experimental station,Hebei province,of China Agricultural University,to investigate the effect of plant density on yield and fiber quality of cotton with sympodial branches,with hybrid cotton Xinza2 and conventional cotton Guokang12 as materials.The results showed that there was no significant difference in seed cotton yield between cotton with and without sympodial branches at medium density(60000 plants.hm-2) in 2004,characterized by less rainfall.However,yield of seed cotton with sympodial branches significantly reduced 13.4% compared to that without sympodial branches in 2005,characterized by excessive rainfall during blooming stage,mainly due to fewer bolls per plant.Compared to Guokang12,Xinaza2 was less susceptible to rainfall.Additionally,the reservation of sympodial branches could decrease fibre micronaire value.With the increase of population density from 15000 to 120000 plants.hm-2,the yield of seed cotton with sympodial branches increased at first,while reached the peak at about 60000 plants.hm-2,then decreased.Nevertheless,there were no significant differences in yield among population density from 30000 to 90000 plants.hm-2.The change tendency of boll numbers per unit area with population density was similar to that of yield,and boll numbers per plant and boll weight reduced significantly with the increase of density.Moreover,high density could reduce the micronaire value of cotton.It was concluded that 60000 plants.hm-2 is appropriate for the cultivation of cotton with sympodial branches in the North of the Yellow River area,but it is necessary to avoid excessive vegetative growth during overcast and/or rainy period.

The invention discloses a novel purpose of gamma-aminobutyric acid in the application of increasing the temperature stress resistant ability of plants. The method of increasing the temperature stress resistant ability of plants is to use gamma-aminobutyric acid to treat plants by soaking and/or foliage spraying. The invention further discloses the applications of gamma-aminobutyric acid on promoting growth, and/or, increasing productivity, and/or increasing quality of plants. Experiments show that it is able to, through the processes, such as seed treatment, foliage spraying using the gamma-aminobutyric acid of a certain concentration, increase the endurance of crops, decrease hazard from temperature stress, such as high and low temperatures, and reduce loss of production.

Recently,premature senescence caused by potassium deficiency has become an important problem in cotton production throughout the Huanghuaihai Plain,China.Therefore,field experiments were conducted in Wuqiao,Hebei Province and Xiajin,Shandong Province in 2004.These were carried out to investigate the effects of K fertilizers on yield and yield components of transgenic insect-resistant cotton and conventional cotton.The content of exchangeable potassium in the soil of Wuqiao and Xiajin were 100 and 130 mg·kg~(-1),respectively.The varieties of transgenic insect-resistant cotton used in Wuqiao included DP99B,Jimian668,CCRI 41 and Handan284,in Xiajin included DP99B,Jimian668, Lumianyan21 and Lumianyan22.The varieties of conventional cotton used at the two sites were all CCRI 12 and CCRI 35.By applying 600 kg·hm~(-2) KCl before sowing,the results showed that seed cotton yield averaged across all varieties was increased 20.4% and 6.4% in Wuqiao site and Xiajin site respectively.The number and weight of bolls located in the top sympodial branches(≥10) and the outer nodes(≥3) were enhanced by potassium fertilizer more greatly than those located in the bottom(1～5) and medium(6～10) sympodial branches and inner nodes(1～2).It's noteworthy that there weren't any significant differences between transgenic insect-resistant cotton varieties and conventional cotton varieties in their sensitivity to potassium fertilizer under conditions of this research.Because the content of exchangeable potassium in the soil of the two sites exceeded 90 mg·kg~(-1),the lowest value of potassium supply normally in general soil,there was a need to study further the sensitivity to potassium fertilizer of transgenic insect-resistant cotton varieties under potassium deficiency conditions.Furthermore,this research screened the optimal quantity of potassium fertilizer in Huanghuaihai Plain,and found that applying 150 kg·hm~(-2) KCl could get a great benefit while the exchangeable potassium in soil was 100～130 mg·kg~(-1).