| Controlled-release fertilizer and biochar amendment has been shown to increase crop yields and nutrient use efficiency(NUE)in a number of production systems.However,understanding the effect of controlled release fertilizers and biochar on leaf photosynthesis and NUE of cotton is currently limited.A 4-year located-field experiment applied 50%(100 kg ha-1),100%(200 kg ha-1)and 150%(300 kg ha-1)of the local practice N rates with CRU and urea was conducted under the cotton-garlic intercropping system in Shandong Province,China.Meanwhile,effects of potassium fertilizer rates and biochar rates on crop yield and soil fertility were studied in the same region.There were four treatments,which was: CK(K2O 0 kg hm-2),K90(K2O 90 kg hm-2),K180(K2O 180 kg hm-2)and K270(K2O 270 kg hm-2).To investigate the effect of successive biochar amendment at four rates,i.e.,0,5,10 and 20 t ha-1 on cotton yield and soil nutrients distribution in 0-100 cm soil profiles.Besides,a 3-year pond experiments were conducted consecutively with Six K treatments: basal application of potassium chloride,potassium sulphate,50% basal and 50% top-dressing at full bloom stage of potassium chloride,basal application of potassium chloride with sulfur,basal application of controlled release potassium chloride and controlled release potassium chloride with sulfur.Furthermore,incubation experiments applied CRU and Urea with 0%(0 mg N kg-1soil),50%(110 mg N kg-1 soil),75%(165 mg N kg-1 soil),100%(220 mg N kg-1 soil),125%(275 mg N kg-1 soil)and 150%(330 mg N kg-1 soil)of the recommended N fertilizer rate were conducted to explore the effects of CRU on soil NH3 volatilization,NUE,and cotton yield.A two-year pot experiment was consecutively conducted in 2014 and 2015 with three kinds of potassium fertilizer including potassium sulfate(KPS),potassium chloride(KPC)and polymer coated potassium chloride(CRK),each at four application rates(0,1.04,2.08 and 3.12 g K2 O plant-1,respectively).A two-year pot experiment was consecutively conducted in 2014 and 2015 with three kinds of potassium fertilizer including potassium sulfate(KPS),potassium chloride(KPC)and polymer coated potassium chloride(CRK),each at four application rates(0,1.04,2.08 and 3.12 g K2 O plant-1,respectively).In addition,to investigate the interacting effects of different carbon sources(C)and nitrogen sources(N)on cotton growth,an experiment was conducted with containerized plants in 2014 and 2015.There were three kinds of N sources(without N source,urea and CRU)each combined with three C sources(without C sources,straw and biochar).(1)Results showed that the cotton yield increased with higher nitrogen appilcation.The cotton yields of Urea and CRU with the N rate at 200 and 300 kg·hm-2 were all significantly higher than that of 100 kg·hm-2.The cotton yields in CRU treatment were 17.3% and 7.7% higher than Urea with the same nitrogen rate at 200 and 300 kg·hm-2,respectively.The NO3--N concentration of soil(0-20 cm)in CRU treatment was significantly higher than that of Urea.Soil NH4+-N content was not affected by the N fertilizers.Cotton yields of CRU100% were 7.7% and 14.5% higher than those of Urea100% and CRU50%,respectively.The linear increase in garlic yield and curvilinear increase in cotton yield indicates that crop yields increased as the input N rate increased with both urea and CRU while exceeded N application decreased cotton yields.The NO3--N contents of CRU treatments were augmented in 0-40 cm soil compared with urea treatments,but the opposite trend was found in 60-100 cm soil.The organic matter and total N contents in 0-40 cm profile were increased with CRU fertilization over 4-year fertilization.Results indicate that the N release characteristic of CRU in soil closely conforms to cotton demand for N over its entire growth period.Ammonia volatilization was reduced by 65.1%-104.9% with CRU in comparison to urea treatments at the same N rates.As a result,CRU treatments achieved significantly higher lint cotton yield by 7.2%-30.2%,and the NUE of CRU treatments was increased by 25.0%-124.0% relative to that of urea treatments.For each type of N fertilizer,the NH3 volatilization,lint cotton yield,and NUE increased with the rate of N application,with NUE reaching a threshold and decreasing when N application rates of urea and CRU exceeded 238.7 and 209.3 mg N kg-1 soil,respectively.Soil inorganic N contents,leaf SPAD values,and net photosynthetic rates were significantly increased by CRU application,particularly from the full bloom stage to the initial boll-opening stage.(2)Results indicated that the K release characteristics of controlled release potassium chloride(CRK)in soil condition were closely matched to the K requirement of cotton.The contents of soil available K in CRKS treatment were significantly higher at initial boll-opening stage and harvest stage than in the CK1 and CK2 treatments.Soil water-soluble K and exchangeable K contents increased while non-exchangeable K contents decreased with CRKS fertilization compared with CK1 and CK2 treatments after three year fertilization.Meanwhile,the SPAD value and net photosynthetic rate of function leaf in CRKS was also significantly enhanced,especially after boll stage.The lint yield of CRKS treatment was 16.9%-24.9% higher than CK1,24.4%-30.9% higher than CK2,12.2%-16.1% higher than 50% basal and 50% top-dressing of potassium chloride potassium chloride(KClD),but no significant difference observed between CRK and KClD treatments in all the three years.The release characterizes of potassium from CRK corresponded well to the potassium requirements during cotton growth.The contents of soil available potassium,as well as leaf SPAD values,net photosynthetic rate(Pn),maximal photochemical efficiency(Fv/Fm)and effective quantum yield of photosystem II(?PSII)in CRK treatments was increased after full bloom stage compared with conventional potassium fertilizers under the same potassium application rate.For each type of potassium fertilizer,the yield and potassium uptake of cotton increased but the KUE decreased with higher potassium application.Consequently,the CRK treatments significantly increased lint cotton yields by 8.1%-32.7% and 3.7%-20.8% while the KUE increased by 15.5%-54.8% and 14.5%-45.4%,compared with KPC and KPS treatments,respectively.The results indicate that the application of CRK is intensively recommended to replace conventional potassium fertilizers for gaining greater yields and higher KUE of cotton.(3)Biochar enhanced lint cotton yield by 8.0%-15.8%,9.3%-13.9% and 9.2%-21.9% in 2013,2014 and 2015,respectively,while high levels of biochar application achieved high cotton yields each year.The fiber length and elongation rate in BC20 were significantly higher than the Control in 2014 and 2015.The leaching of soil NO3--N was reduced,while the pH values,soil organic carbon,total N and available K contents of 0-20 cm soil were increased in 2014 and 2015.However,the changes in soil available P content were less remarkable.The effects of biochar addition on cotton yield were greatly dependent upon the biochar application rate,mainly associated to its nutrient content due to the low fertility of the soil used.However,cotton yield of biochar amendment treatments increased by 6.8%-32.3% in relation to biochar free treatment.However,1% biochar application treatment produced the higher yield as with the 2% biochar application treatment,possibly through a reduction of the availability of soil P and a elevation of soil C/N,indicating that higher biochar successive amendment with moderate N fertilizer application could reduce cotton yields in soils with a low indigenous N supply.The fiber length,fiber elongation and strength were enhanced with biochar amendment,but the micronaire and fiber uniformity was not affected.In addition,leaf chlorophyll values(SPAD)and photosynthetic rates(Pn)were enhanced by biochar amendment in the late cotton growth period.The results suggested that soil inorganic nitrogen contents were significantly increased by using CRU instead of urea,and the same trend was observed with leaf SPAD values.Meanwhile,the bolls and lint yields of cotton in the CRU treatments were increased than urea treatments.Soil pH values,soil organic carbon,total N,available K contents and C/N ratio were increased with Biochar.Lint yields also increased by 9.1%-12.7% with biochar compared with the straw treatment at the same nitrogen source.Hence,application of CRU combined with biochar on cotton increased the yields and fertilizer use efficiencies in addition to improving fiber quality and delaying leaf senescence.(4)Results indicated that the bolls and boll weight under CRF1 and CRF2 treatments were increased compared with CK.Seed cotton yields in CRF1 and CRF2 were 10.2%-21.9% and 18.15%-25.24%,respectively,higher than CK.Although there was no significant difference between CRF1 and Urea,CRF1 was much labor savable.Fiber length and strength were improved by CRF2 fertilization when compared with CK,indicates that CRF2 is an effective approach to increase fiber quality.The contents of nitrate andavailable K were higher in 0—20 cm soil of CRF2 treatments than CK over 2-year fertilization.These results suggest that the basal application of controlled release urea and controlled release potassium chloride on cotton increased the yields and fiber quality in addition to improving soil fertility. |
PDF Full Text Request