Effect Of N Rate On Yield Formation And Nutrients Utilization Of Summer Direct Seeding Cotton

To make sure the feasibility of reduce further nitrogen fertilizer under the condition of late sown,high density,once fertilization(first flower),2-yr field and pot experiments with five N rates(120,150,180,210,240 kg ha-1)were carried out by adopting Huamian3109(G.hirsutum L.).Parameters were studied such as cotton biological characteristics(growth,yield and its component,biomass accumulation),physiological(SPAD,nitrate-nitrogen,free amino acid,soluble sugar and soluble protein),as well as the utilization of mineral nutrients.The results showed that: 1.Cotton yield and its componentsCotton yield increased with the increase of nitrogen application,but it has increased upto a certain extent and thereafter yield increment is not obvious(1370 kg ha-1 180 kg ha-1),However boll weight and lint percentage remain unaffected.2.Cotton growth process and agronomic charactersDifferent amounts of N applications had no effect on cotton growth,seedling and squaring,but boll setting period extend 1-2 d with increased N application,Pot and field trial had same trend.Increase in the amount of nitrogen fertilizer has a significant influence on plant height,cotyledon diameter of fruit branch length,number of branches however climatic conditions also had considerable impact on cotton agronomic attributes.3.Dry matter accumulationCotton plant and different organs biomass followed the normal “logistic” growth curve.Accumulation speed increased with 120-180 kg ha-1 and further increase in nitrogen application will have a little effect on accumulation speed while increase in nitrogen application.4.Nutrient(NPK)accumulationand nitrogen partial productivityNitrogen and biomass accumulation synchronised with each other followed by potassium however phosphorus accumulation appeared prior to nitogen and potassium.Nitrogen application at 180 kg ha-1 nitrogen assimilation rate was higher and it remained steady or decreased with enhanced nitrogen application.5.Thephysiological and biochemical characteristicsSPAD value remains unsteady prior to fertilization but increased rapidly after fertilizer application and remains steady after flowering and boll opening however SPAD value declines as the temperature reduced.Nitrate nitrogen and soluble sugar contents had a very little affect by fertilizer application though amino acid and protein had a significant effect.Amino acid contents enhanced considerably at flowering and boll setting period however soluble protein increased at boll opening stage,respectively.