Phosphorus Supply In Black Soil And Effect Of Plastic Film Mulching And Phosphate Fertilization On Maize

Black soil is an important soil resource in China. Phosphorus(P) is an essential element for all living organisms. P deficiency is one of limiting nutrients to crop production due to its low solubility, easy fixation and relative immobility. Since last century, P levels in black soils have greatly increased under the conditions of high Pi supply in the intensive agricultural production system. The study of soil P forms and transformation is greatly significant to increase utilization of accumulated P in soils by plants and to reduce P loss in agricultural ecosystems. In this study, four treatments which was taken from Gongzhuling, Jilin at maize harvest stage in 2008, including NK(nitrogen and potassium), NPK, NPKM(NPK + manure), NPKS(NPK + straw) in the long-time fertilizer trial were selected. Solution 31 P nuclear magnetic resonance(31P-NMR) and chemical sequential fractionation were used to determine P forms in black soil. Batch experiment was conducted to reveal the characteristic of P adsorption and desorption behaviors under different temperature conditions(10℃, 15℃ and 25℃). Field experiment was carried out in 2013 and 2014 to investigate effects of P fertilization and plastic film mulching(PLM) on maize growth, yield and soil P availability. The objectives were aimed to assess the ability of P supply in black soil under continuous P fertilizer input and the influences of PLM on the transformation of P in soil and the uptake of P by maize. The results were showed as following:Long-time NK fertilization treatment had lower concentration of total P and available P compared with other treatments under P fertilization. According to the method of Guppy soil P fractionation, long-time NK fertilization treatment had the lowest contents of inorganic and organic P forms as Resin-P, Na HCO3-P, Na OH-P, HCl-P, and long-time NPK + manure treatment had the highest contents.Studied by solution 31 P nuclear magnetic resonance(31P-NMR) spectroscopy, orthophosphate, orthophosphate monoesters and pyrophosphate were detected in the tested black soil. Orthophosphate and orthophosphate monoesters accounted for most of total extracted P amounts. Solution 31P-NMR results showed that NK treatment soil had less orthophosphate and higher percentage of orthophosphate monoesters in total extracted P amounts than other P treatments. The contents of orthophosphate and orthophosphate monoesters increased significantly under long-time NPKM application. Conversely, the percentage of orthophosphate monoesters in total extracted P amounts declined markedly.Low temperature restrained the P adsorption and desorption by the tested black soil. In low temperature, the adsorption coefficient of black soil did not alter significantly, however, the maximum adsorption capacity, the maximum buffer capacity and the extent of absorption decreased significantly. Low temperature also lowered P desorption in black soil and thus inhibited the release of adsorbed P.There were no significant differences of maize yields and soil available P concentrations of soil between the treatments of 75 kg P2O5/hm2 and 60 kg P2O5/hm2 in two years of field experiment.Under PLM treatment during maize seedling stage, the soil temperature and humidity were increased, shoot biomass, root biomass and plant P uptake of maize were significantly improved and available P content of rhizosphere soil was increased. However, these promoting effects of PLM treatment were not showed at the maize harvest stage. There was no significant difference in maize yield between the treatments with and without PLM during the two years.According to 31P-NMR spectroscopy, orthophosphate, orthophosphate monoesters and pyrophosphate were detected in the soil samples under PLM treatment during the maize seeding stage. The contents of total extracted P and orthophosphate in rhizosphere soil were higher than those of non-rhizosphere soil. The treatment with PLM had higher contents of total extracted P, orthophosphate, orthophosphate monoesters and pyrophosphate both in rhizosphere soil and non-rhizosphere soil than those without PLM.This study concluded that the long-time application of inorganic P fertilizers and organic manure could significantly increase the contents of total P, available P and different forms of P. However, without P fertilization, soil available P supply significantly decreased. The low temperature restrained P adsorption and desorption in black soil. Plastic film mulching during maize seeding stage could increase soil P supply and promoted the growth and P accumulation of maize plants.