Effects Of Nitrogen Fertilizer And Plant Density On Cotton Yield And Its Formation Under Two Ecological Conditions

Cotton is a tropical crop and plays a considerable role in the economic development worldwide.Cotton is an important source of fiber,oil,and animal feed.It plays a significant role in the country's economy because of its high quality fiber.For efficient cotton production,it is very important to understand the response of cotton growth,development and yield to various management practices.A number of factors such as plant density?PD?,and nitrogen?N?are considered as crucial factors that influence cotton production significantly.N is a major nutrient for sustainable production of cotton and is very important for photosynthesis,enlargement of canopy and enhance cotton yield by enhancing number of bolls per plant.PD is often practiced to overcome input costs without sacrificing yield.It was reported that rural employment decreased from 355 million in 1995 to 314 million in 2007 in China,but the labor off-farm employment ratio to the total employment increased from 33%in 1986 to 63%in 2008 in China,resulting in increased labor costs in agricultural production.However,the problem could be solved by the study's hypothesis that one application of fertilizer with suitable planting density should result in no yield reduction if the fertilizer is applied at the suitable time in late sown cotton when the plant requires it most.The main objective of this study was to find the optimum combinations of planting density and nitrogen application rate for the efficient production of cotton crop.The study was conducted at two locations,China and Pakistan during the year 2015 and 2016 respectively.The experiments were designed in randomized complete block design with a split-plot arrangement,where the main plot was N rate and the sub plot was PD.There were two N levels;low nitrogen?LN?120 kg ha^-1 and high nitrogen?HN?180 kg ha^-1 and three levels PD;8 plants m-2 as low density?LD?,10 plants m-2 as medium density?MD?and 12 plants m-2 as high density?HD?.In this study,we observed the response of N and PD and their interactive effects on physiological,agronomical attributes and total N contents of cotton at different development stages.The results showed that:1.Cotton growth and total N contents were varied among treatments and among different development stages.Significant N and PD interaction was also found on plant growth,leaf gas exchange and yield.2.Plant biomass production,photo synthetic rate?Pn?,intercellular CO₂?Ci?,water use efficiency?WUE?and total N contents were unaffected by N application and PD at seedling stage,nonetheless highest Pn and Ci and total N contents were observed at squaring stage followed by blooming stage.3.Among treatments,higher N contents were obtained with LN with HD and HN application with MD.Among growth stages,we found that squaring stage is more crucial followed by blooming stage for N contents while considering N application rate and PD.4.Higher plant growth and cotton yield was noted under LN with HD than other treatment combinations.Maximum values of leaf photosynthesis,stomatal conductance?gs?,Ci,Ts and WUE were obtained under LN with HD or HN with MD,while the least values were observed under LN with LD.Correlation analysis revealed highly significant and positive relation between leaf gas exchange and cotton yield.5.In Pakistan,a Pakistani cultivar FH-142 took more days to reach maturity as compared with Chinese cultivar Huamian-3109.FH-142 produced higher seed cotton and lint yield under high N application with MD.6.Low N with HD or high N with MD harvested the highest yield for two locations of Hubei China and Punjab Pakistan and two cotton cultivars of Huamian 3109 and FH-142,although great differences were existed between two locations and between two cultivars.It is suggested that these combinations be better for each of cotton cultivars under different agro climatic conditions of China and Pakistan.