Cotton Yield Formation And Nutrients Utilization Response Mechanism To K To N Ratio

Nitrogen(N)and potassium(K)are the major mineral nutrients demanded by crop plants,which are crucial for cotton yield and fiber quality.High N amount and low K to N ratio(KNR)are very common in cotton production,resulting in low profit,low fertilizer use efficiency and environmental concern.It is urgently needed to discuss the optimal KNR in the 3 cotton regions combined with cotton nutrients demand and soil nutrient supply when N amounts were reduced under the light and simplified cotton cultivation.Field experiments were conducted separately in Wuhan(2016-2017),Anyang and Alaer(2018-2019).The research focused on cotton responses in yield formation,nutrients utilization to KNRs(0.8,1.0 and 1.2 in the Yangtze River Valley cotton region(Wuhan)and 0.5,0.9 and 1.3 in the Yellow River Basin cotton region(Anyang)and the Northwest Inland cotton region(Alaer).Results showed that the optimal KNRs are 1.0 for Wuhan and 0.9 for Anyang and Alaer,because these KNRs:(1)Benefit the cotton canopy establishment.Higher KNRs increased canopy interception rate of photosynthetically active radiation(Ir)by 7.4-18.6% and 0.3-21.2% at the top of canopy,and 8.1-24.1% and 3.3-34.7% at the middle of cotton rows in Anyang and Alaer,respectively,at peak bloom stage.However,excessively high KNR caused canopy shading with low transmittance rate of photosynthetically active radiation(PAR)at the bottom of canopy.(2)Promote cotton biomass accumulation and partitioning.Higher KNRs increased the cotton biomass accumulation by 7.3-18.6%,5.7-27.4% and 6.5-11.0% in cotton plant biomass(CPB)and by 6.3-18.4%,8.6-18.0% and 7.9-11.5% in cotton reproductive parts biomass(RPB)in Wuhan,Anyang and Alaer,respectively.Furthermore,the increase of KNRs promoted 0.1-3.8% more cotton biomass distributed into reproductive parts and increased the harvest index by 6.0-13.5%.The initiation and termination of cotton reproductive parts biomass accumulation were earlier in higher KNRs,which was accompanied by earlier biomass transportation to the reproductive parts.(3)Benefit cotton source and sink relationship balance.Cotton leaf area index(LAI)was 8.0-35.0% and 10.3-13.5% higher and boll load was 0.7-5.4% and 0.1-4.8% lower in Anyang and Alaer,respectively,in higher KNRs.LAI had positive relationship with cotton yield.Increasing KNR could promote carbohydrate synthesis in leaves and carbohydrate accumulation in cotton plants with 4.5-18.9% higher net assimilation rate(NAR)and 11.7-44.6% higher cotton growth rate(CGR).Meanwhile,the increase of KNR could promote carbohydrate transportation from leaves to reproductive parts with 3.0-22.8% and 5.2-14.1% lower specific leaf weight(SLW)and 0.6-2.3% and 1.1-7.2% lower biomass distribution proportion in leaves in Anyang and Alaer,respectively.And the reproductive parts growth rate(RGR),sucrose transformation rate(STR)in the functional leaves and sucrose/starch ratio increased by 13.4-35.8%,19.2-37.8% and 5.0-28.7%,respectively,in higher KNRs.Moreover,higher KNRs increased boll retention percentage(BRP)in the middle fruiting positions and outside fruiting positions(OFP)by 9.7-17.0% and 9.6-48.8%,respectively.However,excessively high KNR might cause canopy shading,resulting in 9.6% higher boll shedding percentage(SSP)and 1.4-4.7% lower boll density,which was not conducive to balance cotton source and sink relationship and yield formation and LAI had a significant negative correlation with yield in this case.(4)Increase cotton nutrients accumulation and partitioning.The N,P and K accumulation increased by 4.9-38.8%,4.0-31.1% and 4.0-34.2% in Wuhan,5.1-40.6%,8.2-36.5% and 5.1-56.0% in Anyang,and 1.8-4.7%,6.1-7.4% and 1.6-8.0% in Alaer,respectively,in higher KNRs.It is noteworthy that N,P and K accumulation ratio was similar under different KNRs and cotton region with 1: 0.14-0.16: 0.96-1.18 in Wuhan,1: 0.12-0.23: 0.83-1.02 in Anyang and 1: 0.18-0.21: 0.83-0.90 in Alaer,respectively.The N,P and K distribution proportions in reproductive parts showed a Logistic growth and ever-increasing along with effective accumulated temperature.The N,P and K distribution proportions in reproductive parts increased by 1.2-3.7%,4.0-7.2% and 0.3-2.6% in Wuhan,3.0-8.5%,2.9-10.4% and 0.6-10.2% in Anyang,and 1.3-3.7%?5.8-6.7% and 1.8-4.7% in Alaer,respectively,in higher KNRs.Furthermore,there was a significant positive correlation between the BRP in the OFP and the N,P and K accumulation in cotton plant and reproductive parts.(5)Promote cotton utilization of soil nutrients.Higher KNRs accelerates soil nutrient content decline,resulting in a negative correlation between the soil alkali hydrolysable N,available P and available K contents and cotton N,P and K accumulation.Higher soil total N,P and K contents were beneficial to cotton N,P and K accumulation with positive correlations.The application of N and K fertilizer increased soil nutrients contents,and cotton plant nutrients absorption decreased soil nutrients contents gradually along with cotton growth stages.Fertilizer application and cotton nutrients absorption could induce the soil nutrients contents to be stratified in vertical and horizontal positions.(6)Increase cotton yield and fiber quality.Higher KNRs increased cotton yield by higher boll density and boll weight.Higher KNRs had 5.3-11.9%,0.6-18.6% and 6.6-18.7% higher boll density,3.9-8.8%,1.9-3.5% and 1.2-6.9% higher boll weight,and 9.9-24.3%,0.7-22.8% and 5.3-27.1% higher cotton yield,in Wuhan,Anyang and Alaer,respectively.Moreover,higher KNRs significantly improved fiber length,fiber strength,uniformity,elongation and the grade of micronaire.However,further increase of KNR could not significantly improve cotton yield and quality.Therefore,the medium KNR(1.0 in the Yangtze River Valley cotton region and 0.9 in the Yellow River Basin cotton region and the Northwest Inland cotton region)could increase cotton nutrients absorption and utilization,yield and fiber quality,and also be conducive to resources saving,relieve environmental pressure.