Response And Mechanism Of Cotton Yield To Nitrogen And Potassium Fertilization Strategy When Rapeseed Meal Applied At Preplant

To overcome the technical barrier of high cost and low efficiency of conventional seedling transplanting and cotton planting models in the cotton region of the Yangtze River Basin.We proposed a technical approach of“increasing production without increasing investment”.Therefore,based on the streamlined cotton planting model of summer direct seeding,the Hubei Province-promoted cotton variety Huamian 3097 was selected to conduct field experiments during the 2021-2022 growing season.The mechanism of cotton yield formation in response to nitrogen and potassium fertilizer application was explored using rapeseed cake as a substitute for some chemical fertilizers.The current experiment was conducted under a randomized complete block design in a split-plot arrangement where potassium（K）fertilizer application frequency K1（100%pre-plant fertilizer）and K2（50%pre-plant fertilizer+50%first bloom fertilizer）were kept in the main plot and the sub-plots were allocated with nitrogen（N）fertilizers splits N2（20%pre-plant fertilizer+80%first flower fertilizer）,N3（20%pre-plant fertilizer+60%first flower fertilizer+20%peak bloom fertilizer）,N4（10%pre-plant fertilizer+50%first flower fertilizer 30%first bloom fertilizer 10%peak bloom fertilizer）.Pre-plant application of620.0 kg hm^-2 rapeseed cake（containing 3.4%N;1.3%P;1.8%K）replaces N,P,and K fertilizers by 10%,19.2%,and 6.4%,respectively.The results showed that K2N3 proved more effective than other treatments,and the main findings are as follows:1.The K2N3 achieves higher cotton yield and fiber quality.The split application of K fertilizer（K2）took longer time（2 d）to achieve the flowering and boll stages as compared to one-time application（K1）.while N4（N3）is 2 days longer than N2.Therefore,K2N4was statistically at par with K2N3（longest）and 3-4 days longer than K1N2（shortest）.Likewise,seed cotton yield in K2 was higher by 8.5%over K1,and 20.3%higher in N4and N3 as compared to N2 which indicated that K2N4 and K2N3 behaved alike and produced higher seedcotton yield（33.6%）as compared to K1N2 treatment.This yield difference might be attributed to the effective number of bolls in the population.The plants subjected to K2 exhibited improved fiber length and elongation by 3.6%and 2.7%respectively,over K1 application,thus the K2N3 has produced the fiber with the finest quality.2.K2N3 was more effective in terms of biomass accumulation and distribution in cotton plants,as K2 and N4（N3）accumulated more biomass by 8.6%and 20.1%（8.2%）respectively,over their respective controls K1 and N2 Therefore,K2N4 showed the highest values for biomass accumulation followed by K2N3,on other hand,K2N3 demonstrated5.0%more biomass distribution to the reproductive organs than K2N4 regime.However,minimum biomass accumulation and distribution were observed for the K1N2 application.3.The K2N3 has significantly influenced the plant architecture and developed a more desirable cotton canopy structure.An increase in the leaf area index and a decline in canopy light transmittance was recorded from the boll setting to the boll opening stage under the K2 application as compared to K1.A similar trend was also observed for the N application where N4（N3）was more efficient than N2.Which illustrated that K2N4 received the lowest light transmittance and exhibited minimum canopy shading followed by K2N3（moderate）and K1N2（highest）treatment.4.The K2N3 proved to be more beneficial for the accumulation and distribution of mineral nutrient in cotton.The N,P,and K contents of cotton plants were 16.8%,17.5%,and 13.7%higher in K2 than in K1,respectively.In case of N,the N4（N3）application was higher by34.1%（20.6%）,30.2%（15.5%）,and 22.5%（9.3%）than N2,respectively.Therefore,K2N4application resulted in the highest miniral accumulation and distribution followed by K2N3,and K1N2.Moreover,K2N3 allocates more N（3.2%）P（3.1%）,and K（2.2%）to the reproductive organs than K2N4.It was also noted that the difference in cotton nutrients content among treatments was contrary to the difference existed soil nutrient content in cotton fields.5.The K2N3 illustrated a key role in the regulation of carbon and nitrogen metabolism in cotton plants.As compared to K1 and N2,the treatment K2 and N4（N3）have considerably increased the chlorophyll content,Rubisco enzyme activity,and net photosynthetic rate of functional leaves in the later stages of cotton growth,accelerated the output of photosynthetic products,respectively.in addition,the activities of N metabolism enzymes i.e.nitrate reductase,nitrite reductase,glutamine synthetase,glutamic acid synthase,glutamic acid transaminase,glutamic acid transaminase in functional leaves were improved,and the protein content was also enhanced.In crux,the basal application of rapeseed cake fertilizer substitutes some chemical fertilizers,reducing the application rate of N,P,and K under summer direct seeding simplified cotton planting model Two applications rates of K fertilizer combined with three levels of N fertilizer（K2N3）optimize the cotton canopy,regulate carbon and nitrogen metabolism,improve fertilizer utilization efficiency,enhance biomass accumulation and distribution,increase the bolls density in the population and eventually improve cotton yield and fiber quality.So,it is concluded that the present approach is one of the technologies that may cope the current challenges in cotton production.