Effects Of Phosphorus Application Rates On Soil Nutrient Content,dry Matter Accumulation,and Yield Of Cotton

Phosphorus(P)is one of the main limiting factors for cotton yield.Thus,clear P demand for cotton(Gossypium hirsutum L.)growth can provide a theoretical basis for accurate fertilizer application in production.The effects of P rates on soil nutrient content,microbial biomass carbon and nitrogen(N),and enzymatic activities at different soil depths and its combine effect on the dynamic characteristics of biomass,N,P,and K accumulation in the Reproductive organ(RO)of cotton cultivars with different P sensitivity were determined.In this study,a two-year field experiment was conducted using two cotton cultivars with different P sensitivities[low P-sensitive(Lu-54)and low P-tolerant(Yuzaomian-9110)]under three P rates[P0:0,P1:100 and P2:200 kg P2O5 ha-1]in 2017 and 2018.The plant samples were collected at five different times at days after transplanting(DAT)i.e.39,52,69,83,99 at squaring "SQ",first bloom "FB",peak bloom "PB",boll setting "BS",and boll opening "BO" growth stages.The soil samples collected from two soil depths(0-20 cm and 20-40 cm layers)were analyzed for the determination of soil physico-chemical properties,nutrients contents,and soil enzymes activities.The main results are as follows:1.Soil phosphorus enrichment accelerated the phosphatases activity and improved soil phosphorus nutrient content in cottonResults revealed that the P application(P1 and P2)significantly improved the total and available P in topsoil and subsoil at squaring and harvesting stage during both cropping seasons.Similarly,P application improved urease,acid,alkaline,and neutral phosphatase activities at both soil depths at squaring and harvesting stage.However,other soil nutrients such as ammonium(NH4+-N),nitrate(NO3--N),total nitrogen(TN),available potassium(AK),and total potassium(TK)were not significantly changed between different P rates.The microbial biomass carbon(MBC)and N(MBN)in the soil considerably changed with the application of P rate and recorded higher at P2 treatment by compared to P1 and P0 at harvesting stage across the two growing seasons.The findings showed that P2 compared with the other P rates can ensure higher P availability due to better phosphatase enzyme activity,which is conducive to improving the cotton potential to maintain higher productivity.These findings may also help to devise a cost-effective fertilizer management strategy to sustain the soil fertility as well as to improve cotton yield.2.Phosphorus application enhanced the biomass accumulation and yield of the two cotton cultivars with different P sensitivityCompared to P0 treatment,the number of fruiting nodes,number of fruit branches,and boll setting rate in P1 and P2 treatments increased for both Lu-54 and Yuzaomian-9110 during the two years,respectively.Seed cotton yield was improved in P1 and P2 treatments over P0 treatment by 24.0-35.0%and 31.0-52.0%in Lu-54 while 17.0-26.0%and 21.0-39.0%in Yuzaomian-9110 across the two growing seasons,respectively.The P1 and P2 improved the reproductive organ biomass(ROB)in Lu-54 as well as Yuzaomian-9110 across the two growing seasons.During the fast accumulation period(FAP),the average accumulation rate of ROB was recorded as 11.3-44.0%and 32.4-53.3%higher in P1 and P2 treatments for Lu-54,whereas 20.3-60.9%and 38.5-67.5%higher for Yuzaomian-9110,respectively,compared to P0 treatment.The improvement in the average speed of ROB accumulation and maximum ROB accumulation rate resulted in higher seed cotton yield.The dynamics of RO biomass ensued better response of Lu-54 as compared to Yuzaomian-9110 during both cropping seasons.The partial factor productivity(PFP),P agronomic efficiency(PAE),and partial nutrient balance(PNB)decreased by 45.2%,18.3%,and 36.3%,while P recovery efficiency(PRE)and harvest index(PHI)increased by 0.61%and 2.9%in P2 compared with P1 for Lu-54,respectively.The PFP,PAE,PHI,and PNB were lower in P2 compared with P1 for Yuzaomian-9110,while PRE increased.Conclusively,cotton cultivar Lu-54 can obtain maximum rate of ROB accumulation which is beneficial to the formation of final yield than Yuzaomian-9110.3.Phosphorus application improved the nutrient accumulation of the two cotton cultivars with different phosphorus sensitivityResults showed that positive relationships existed between seed cotton yield and N,P,and K accumulation.The P application rates(P1 and P2)decreased the N and K concentration in the RO of cotton in Lu-54 and Yuzaomian-9110 in 2017 and 2018.The P1 and P2 increased P concentration in the RO of cotton by 18.6-25.8%and 0.1-5.6%in Lu-54,while 20.9-32.8%and 12.0-14.8%in Yuzaomian-9110 during the two growing seasons,respectively.The increases in RO N,P,and K accumulation caused by P application were higher in Lu-54 compared with Yuzaomian-9110 across the two growing seasons.During the fast accumulation period(FAP),the average accumulation rate of N,P,and K in RO at P2 were increased by 15.4%,71.4%,and 16.3%in Lu-54,while 18.2%,100%,and 11.6%in Yuzaomian-9110 compared to P0,during both seasons,respectively.The starting and termination day of FAP of N,P,and K accumulation in cotton plants RO at P2 rate were earlier,while the accumulation rate per day was recorded higher compared to the other P rates.Moreover,P2 rate increased the N accumulation more significant in middle reproductive organ(MRO)as compared to lower reproductive organ(LRO)and upper reproductive organ(URO),while the P and K accumulation recorded higher in LRO followed by MRO and URO during the two years.The comparison between the two cultivars showed that above parameters about nutrients accumulation in low P sensitive cultivar(Lu-54)were more responsive to P application to obtain the higher seed cotton yield in comparison with the low P tolerant cultivar(Yuzaomian-9110).Conclusively,Lu-54 resulted in higher accumulation rate of nutrients(N,P,and K)to enhance the seed cotton yield as compared to Yuzaomian-9110.Hence,the starting and termination day of fast accumulation period of ROB and nutrient(N,P,and K)in cotton plants RO at P2 treatment were earlier and faster,which was conductive to ROB and nutrients accumulation in cotton plant.The cotton yield and its components including number of fruiting nodes,fruit branches,and boll setting rate were sensitive to P rates.Seed cotton yield recorded higher at P2 than other P treatments due to higher average speed of ROB accumulation and maximum ROB accumulation rate.However,the low P sensitive cultivar(Lu-54)was more responsive to P application for higher seed cotton yield in comparison to low P tolerant cultivar(Yuzaomian-9110).