Mechanism For Efficient Utilization Of Phosphorus And Yield Increasing Of Coated Phosphate Fertilizer Combined With Synergists In Wheat And Maize Growth System

Phosphorus(P),one of the most important macronutrients,is crucial for plant growth and agricultural production.P deficiency is a common phenomenon in agricultural soils worldwide.Low P availability in soils is often due to sorption,precipitation(typically by reaction with Al³⁺and Fe³⁺in acidic soils and Ca²⁺,Mg²⁺in calcareous soils)or microbial immobilization.Despite long-term application of phosphate fertilizers to increase crop yields,P availability is often low,due to the high affinity of phosphate for the soil solid phase.Soil P often needs to be replenished repeatedly to satisfy plant demand in the forms of phosphate fertilizers.However,excessive fertilization has caused potential harm to the environment,such as water eutrophication and soil quality degradation,as well as low P use efficiency(PUE).Controlled release P fertilizers(CRP)improve the availability of P fertilizers by lowering the effective surface area available for contact with Al³⁺,Ca²⁺,Fe³⁺,and other cations that immobilize P.CRP is designed to synchronize the nutrient release rate with crop demand,thereby increasing nutrient uptake for crops and reducing nutrient losses,leaf burning,and environmental pollution.However,continuous nutrient supply only meets the needs of crops in different growth periods,and cannot fundamentally solve the problem of physiological obstacles caused by drought,disease,and extreme weather.The synergists may act as an elicitor in promoting crop growth and protecting crops from abiotic stress and pathogens.However,there were no reports that were available for the combination of controlled release P fertilizers and synergists with wheat and maize.In this study,the humic acid and Paecilomyces variotii extracts were selected as fertilizer synergists.The release characteristics of CRP in wheat and maize growth season were clarified through the incubation experiments in the laboratory and field.Then the effects of CRP combined with humic acid or Paecilomyces variotii extracts were evaluated on the yields and PUE in the pot and field experiment,and the mechanism of high efficiency utilization rate of P fertilizer on the wheat and maize were revealed,which included nutrient supply intensity and physiological characteristics in regulating crop growth.The main results were as follows:(1)During coating,the rough surface of diammonium phosphate(DAP)particles might cause uneven membrane formation,incomplete coating,and excessive accumulation of coating materials in the holes.The water and wax modification of DAP significantly improved the properties and controlled-release characteristics of coated DAP(CDAP).Then the DAP particles were coated with polyurethanes prepared from castor oil.The cumulative release curve from CDAP in the laboratory(25?water)showed an accelerated nutrient-release stage and ended with a stage of reduced nutrient-release.In addition,the CDAP treatments reduced the leaching rate of soil available-P by 96.8%compared with DAP treatments and increased the soil available-P content in 0-40cm soil layer.(2)The differences of N release characteristics between 25°C water in the laboratory and in field soils were probably due to the temperature differences in the study.The differences of nutrient release characteristics between wheat and maize growth season:the cumulative release rate for CDAP reached 84.1%in 220 days during the wheat growth season and 93.8%in 105days during the maize growth season.In the pot experiment,the application of CDAP significantly increased the soil available-P content at the key growth season of wheat and maize,especially during the later growing stages.Sufficient nutrient supply is a requirement for high crop yield.And the application of CDAP improved the SPAD value of leaves at re-greening stage during wheat growing season and jointing stage during maize growing season.Finally,the CDAP treatments increased the yield of wheat and maize by 8.9%-16.0%and 10.5%-11.3%,while the PUE by 3.4-9.1 percentage points and 20.5-28.3 percentage points,and the net income by 12.7%-17.4%and 11.6%-11.7%,respectively,compared with the DAP treatments at the same P rate.Moreover,the application of CDAP were used for achieving the purpose of reducing the P fertilizer rate without reducing the crop yield though 20%less P was applied in these treatments,and significantly improved the PUE and the net income.(3)The activation of humic acid(HA)extracted from danty using hydrogen peroxide(H₂O₂)as oxidizer and birnessite-Mn₂O as catalyst.The activated HA features lower molecular weight and richer functional groups than the danty and HA extracted from danty without the catalyst.After the HA added in soil,the soil structure was improved with increasing of the macro-aggregates(?0.25mm),and the soil water content was enhanced by 5.0%compared the treatments without HA added.In addition,the soil soluble nutrients(eg.P,K)content were also increased in soil.In the pot experiment,the combination of CDAP and HA improved the photosynthetic physiology of crops,and regulated the genes in photosynthesis,hormone,and osmolytes.Moreover,the CDAP combined with HA enhanced the soil available-P supply intensity,and increased the yield by 8.0%-17.5%in wheat and 2.0%-2.8%in maize,while the PUE by 8.3-8.9 percentage points in wheat and 1.1-3.4 percentage points in maize compared with the CDAP alone.During the maize growing season,the CDAP combined with HA increased the activity of PEPC,ATP synthase,and PPDK,then increased the photosynthetic rate at the key stage.(4)The coated diammonium phosphate combined with ZNC provided an emerging green fertilization technology that could reduce losses of P to the environment,improve root and shoot growth,enhance abiotic stress tolerance,and increase the grain yield and net income.The combination of coated diammonium phosphate and ZNC improved the spatial distribution of roots in the 0-40 cm soil layer and the group growth of shoots by regulating hormone content from roots and leaves.In addition,under the low temperature of spring especially during key vegetative stages,the application of coated diammonium phosphate combined with ZNC enhanced POD,SOD,and CAT activities to reduce H₂O₂ content and relieved the damage of leaves.The synergistic effects of CDAP combined with ZNC performed superior to coated diammonium phosphate and significantly improved the photosynthetic rate,and consequently increasing P uptake and improving the accumulation of dry matter of crop grain.The yield and PUE of CDAP combined with ZNC were significantly more than for CDAP by 6.0%and 9.3%in wheat.Although the average yield of CDAPZ treatment was significantly higher than that of DAP treatment by 8.2%,there was no significant difference between yields of CDAP and CDAPZ treatments.This may be due to maize has been defined as an efficient P uptake crop in association with high temperature and large amount of rainfall in summer and a high microbial activity.In summary,the CDAP coated by polymer can reduce the ineffectiveness of P due to the fixation of phosphate by the soil solid phase,and release the nutrient slowly to match the regularity of crop demand.In addition,the combination of CDAP and synergists promotes crop growth and improves the resistance of crop to abiotic stress.This study provides the needed technical basis for the development and application of synergists enhanced fertilizer as a green environmental technology.