Cotton Response To Nitrogen And The Mechanism Of Efficient Utilization To Nitrogen Fertilizer

It is the necessary requirement for agricultural sustainable and efficient development to increase output without an increase of input or to decrease input without a decrease of output, to enhance the efficiency of four items-material, human work, space (field) and time (season), and to alleviate the burden to the environment. Based on the pending issues in cotton production of low utilization rate in N (fertilizer), profit dropping accompanied with cost rising of production, and aggravating in agricultural surface pollution such as eutrophication, the paper stresses on optimizing N rate, the feasibility of N late application and minimum application frequencies in Hubei cotton production area, to provide principles for ways to increase N utilization rate and decrease production cost. By adopting Huazamian H318(Gossypium hirsutum L.), four experiments were carried out in2008-2009:1) N rate (0-600kg/ha) effect on field grown cotton features in biology (especially seed cotton yield) and physiology under different soil fertilities (sites)(Wuhan, Jingzhou);2) pot grown cotton absorption and distribution features for N (fertilizer) applied at different stages (preplant, first bloom, peak bloom) under different N rate (0-600kg/ha) by labeling15N;3) biological and N absorbing responses of direct sown cotton after rapeseed harvested to N late application (split ratio) by fixing N rate at225kg/ha and the ratio for first bloom application (FBA) at40%in field grown and pot grown (15N labeling) conditions, respectively;4) biological response of direct sown field grown cotton after rapeseed harvested to fertilization frequencies (once at FBA, twice at preplant application (PPA) and FBA50%each, thrice at PPA, FBA and peak bloom application (PBA) at30%,40%and30%, respectively) by fixing the fertilization rate at750kg/ha of compound fertilizer (16:16:16). The main results were:1. Cotton growing period was not affected by N application split ratio or fertilization frequencies if N rate was fixed, but the seedling period was shortened and the flowering and boll setting period was extended as N application was postponed (PPA ratio was decreased), or when fertilization was carried out once. Pot grown cotton had a (15-20d) shorter growing period than field grown cotton.2. N rate for the maximum biological and economic yield harvested was the medium rate of300kg/ha in normal soil fertility field, but the rich rate of600kg/ha in lower soil fertility field. More than1,200kg/ha of cotton lint was produced with a reduced N rate of225kg/ha and a higher density of45,000plant/ha for direct sown cotton after rapeseed was harvested. When fixing the N rate, cotton both biological and economic yield increased as PPA ratio decreased; economic yield was negatively correlated to root and leaf biomass, and correlated to the biomass of the rest organs negatively before peak bloom stage but positively after that. When fixing the fertilizer rate, fertilization once produced the same (biological and economic) yield as fertilization thrice did, but the higher yield than fertilization twice did significantly. Economic yield difference was derived from boll number per unit ground area, but biological yield difference was derived from the biomass accumulation speed during the fast accumulation period (FAP).3. Cotton plant biomass (CPB) accumulation process could be described by a logistic function, and the coefficients varied from treatments of each treatment implied that they had different accumulation characteristics such as initiating and terminating date and duration of FAP, the speed during the FAP. The accumulation speed of CPB during FAP increased as the N rate increased, and when N rate was fixed, it was increased as PPA ratio decreased, and application once had the same speed as application thrice did but higher than application twice did significantly. Vegetative organs biomass (VOB) accumulation initiated and terminated the FAP earlier than reproductive organs biomass (ROB), but terminated the FAP later than ROB when N rate was higher than medium level.4. Cotton plant accumulated N slowly in seedling, faster in squaring, the fastest in flowering and slowly again after boll open, which could be described by logistic function. Cotton plant accumulation for soil N initiated the fast accumulation period (FAP) earlier and lasted a longer FAP than fertilizer N. Cotton plant accumulated more fertilizer N than soil N, and fertilizer N was mainly distributed to reproductive organs, while the fertilizer N applied at PPA was to the vegetative organs. When N rate was fixed, the absorption speed during flowering and boll setting period and then the amount of N accumulated in cotton plant increased as PPA ratio decreased. Cotton plant initiated N FAP earlier than biomass FAP.5. Up to boll open stage, chlorophyll content in cotton functional leaf increased as the plant development, and as the N rate increased, and the difference in chlorophyll content among N rates was greater in low soil fertility field than medium field. The leaf content of soluble sugar, soluble protein and petiole content of nitrate N correlated positively to N rate, and rose first and then dropped as the development with the highest in flowering. 6. Soil alkaline N content decreased steadily as plant grew, as deepening in the soil, but positively correlated to N rate. For pot grown cotton, fertilizer N utilization rate responded positively, but N soil residual responded negatively to N rate, while medium N rate had the highest N loss rate. When N rate was fixed, as PPA ratio decreased, fertilizer N utilization rate and soil residual increased but N loss rate increased. Fertilizer N applied at FBA had the highest utilization rate, but PPA had the least.The above results suggest that:1. Late planting could result no yield reduction even if a variety with normal growth period was adopted resulting from the flexibility in growing period. Therefore, winter crops could be harvested in a higher yield due to their possible full maturity. Land and growing season was utilized much better.2. Conventional cotton yield could be achieved by lower N rate, later application with later planting and higher density, to meet the requirement of reduction in input without any reduction in yield, and improvement in fertilizer utilization rate and in environmental friendship production.3. Conventional cotton yield could also be achieved by fertilization once at first bloom stage during which the plant absorbed the most nutrients and absorbed them the fastest. Therefore, some management could be got rid of and less work for cotton production could be possible.4. Hence, later planting with a big density and a smaller individual, lower N rate with later and once application and plant residual application could result in a higher utilization rate of resources, a less labor consumption, and a lower production cost, and in the end could realize the target of sustainable and efficient development.