Effects Of Nitrogen And Potassium Fertilizer Allocation Strategies On Cotton Yield Formation

Nitrogen(N)and potassium(K)are the two most important macro elements required for substantial growth and productivity of cotton crop.The application rate of N and K fertilizers drastically affects cotton yield.Therefore,nutrient management is important to increase cotton yield without increasing inputs in Hubei province.A field experiment was conducted in a randomized complete block design with split pot arrangement during growing season of 2021-2022.In this experiment,the early maturing cotton variety Huamian 2270 was subjected to two splits of K(once(K1),twice(K2)application)relative to 3 splits of N(twice(N2),three times(N3),four times(N4)application).The effects of fertilizers split treatments on cotton growth and development,physio-biochemical attributes,yield formation and fiber quality were investigated.The main results showed that:1.The growth period of cotton was not affected by K treatments,thus N application times had prolonged it.Cotton plant positively responded to K2 exhibiting better morphological structure,plant width,and node numbers as comparing to K1.On other hand,the N2 significantly improved plant height,plant width,node number.The plants had responded to split application of K and produced maximum lint yield for K2 under N3,which is 13.0%higher than that of K1N4.The high lint yield might be due to relative increase the number of bolls(m~2)by 6.2-8.6%.In case of cotton fiber quality,K1 and N3illustrated a short fiber index and high fiber strength,respectively,indicating that the fiber quality of K1N3 was higher than that of K2N4.2.Cotton biomass,plants relative response to K applied on later growth stage was greater as indicated by increasing biomass of source,flow,and sink organs by 23.8%,11.4%,and 10.8%respectively.At early flowering stage,N2(N3)>N4;N3(N4)was 5.7-32.4%higher than N2 at stem elongation stage.As compared to K1,the K2 had delayed the end time of rapid accumulation period,(Δt)prolong,and reduced V_T.With the increase of N application times,the start and end time of cotton biomass rapid accumulation period were delayed,and the average accumulation rate and maximum biomass accumulation increased.The N and K accumulation in cotton plant was higher in K1 in sink organ at early flowering stage while during the boll opening period,the K2 showed an increase by 21.2%and 15.1%compared to K1 in source and sink organs.The N,P and K accumulation in cotton plants was greater for N2(N3)at the early flowering stage whereas,under N3(N4)plants showed higher accumulation of nutrients over N2 from the boll setting stage to the boll opening stage.Maximum biomass accumulation was observed for K1N4 at the stem elongation stage while K1N3 and K2N3 illustrated the longest time for accumulationΔt Cotton plants under K2N3 and K2N4 were more efficient to accumulate N,P and K than the plants from other treatments.3.The leaf area index(LAI)showed contrasting behavior as it enhanced with the increase of K application times(from full flowering stage to boll opening stage)while decreased with the increase of N application times(from bud stage to full flowering stage),and increased at boll setting stage and subsequently.Cotton plants supplied with basal does of K exhibit high canopy light transmittance and improved boll opening period.On other hand,increasing time of Napplication resulted in an increase of canopy light transmittance from the initial flowering stage to the full flowering stage,and decreased after the boll setting stage.Cotton chlorophyll content and photosynthetic capacity were higher for the plants grown under split doses of K over K basal dose.In case of N,N2(N3)showed better results before full-bloom stage,while N3(N4)was more effective from boll-setting stage to boll opening stage.At bud stage,treatment N2 for both K application times was more effective for better LAI and photosynthetic capacity,while N4 gave best results at the boll stage.4.The split doses of K had no effects on enzymatic activities and products of carbon(C)and nitrogen metabolism at early growth stage,however it produced significant results on later stages.Likewise results were also observed for N thus N2 and N3 treatments wer e effective from bud stage to early flowering stage,and from full flowering stage to boll o pening stage,respectively.As compared to other treatments,K2N3 promoted Cmetabolism and enhanced N assimilation capacity of cotton plants at boll-setting stage.It can be seen that K2N3 treatment proved more effective as it increased LIA,reduced light transmittance in cotton fields,enhanced chlorophyll content and photosynthetic capacity,promoted the accumulation of C-N metabolites by stimulating the activities of enzymes involved in C-N metabolism,improved nutrient absorption,biomass accumulation,and finally increased cotton yield.