The effects of two different nitrogen fertilizers （urea and NH4C1） with monocalcium phosphate （MCP） on the movement and transformation of fertilizer P in soil microsites along with soil pH changes at different distances from the fertilizer application site were studied in an incubation experiment. A highly acidic red soil （Ultisol, pH 4.57） from south China with MCP fertilizer alone or in combination with NH4C1 or urea was added to the surface of soil cylinders and packed in wax blocks. After 7 and 28 days, the extraction and analysis of each 2 mm layer from the interface of the soil and fertilizer showed that added NH4C1 or urea did not change the movement distance of fertilizer P. However, P transformation was significantly affected （P 〈 0.05）. After 7 days, at 0-8 mm distance from the fertilizer site the addition of urea significantly decreased the water-extractable P concentration; however, after 28 days the effect of N addition had disappeared. Also,at limited distances close to the fertilizer site NH4Cl application with MCP significantly increased acid-extractable P and available P, while with the addition of urea they significantly decreased. Compared with application of MCP alone,addition of urea significantly increased soil pH in fertilizer microsites, whereas the addition of NH4Cl significantly decreased soil pH.
DU Zhen-Yu ZHOU Jian-Min WANG Huo-Yan DU Chang-Wen CHEN Xiao-Qin
Interactions of N, P and K fertilizers in soil-plant systems are widelyrecognized. This study focused on the transformations of monocalcium phosphate (Ca(H_2PO_4)_2) (MCP)with co-application of ammonium and potassium fertilizers in three different soils. The resultsshowed that after 1 d incubation a large portion of the MCP applied in the paddy, calcareous and redsoils became the water-insoluble form and the recoveries of P applied as Olsen P varied greatly inthese three soils. Application of ammonium sulfate ((NH_4)_2SO_4) (AS) or potassium chloride (KCl)reduced WSP significantly the soils with AS more effective than KCl in the calcareous soil, whilethe reverse occurred in the red soil. Meanwhile, in the paddy soil, co-application of the twofertilizers reduced WSP more than when the fertilizers were applied individually. The co-applicationof AS with MCP in the paddy and calcareous soils significantly reduced Olsen P, but the oppositeoccurred in the red soil. The experiment on the effect of different accompanying anions showed thatthe ammonium fertilizers (PNCl and PNS) reduced WSP more effectively than the correspondingpotassium fertilizers (PKCl and PKS) in the calcareous soil due to the difference of the cations,whereas in the red soil, the chlorides reduced WSP more effectively than the sulfates. Overall,co-application of ammonium or potassium fertilizers with MCP significantly decreased availability ofP from MCP during its transformation in soils, especially when MCP was applied in combination withammonium in the calcareous soil.
Phosphate release from three selected soils after treatments of 1.6 and 2.4 mmol L-1 P was investigated using sequential extractions and fitted using six kinetic models, including zero order (Z), first order (F), second order (S), parabolic diffusion (PD), two constant rate (TC), and Elovich type (ET) equations. The results showed that the rate of P release was initially rapid and then gradually declined with time. Also, P release increased with added P. Total P release followed the order: paddy soil with 2.4 mmol L-1 P > red soil with 2.4 mmol L-1 P > paddy soil with 1.6 mmol L-1 P > fluvo-aquic soil with 2.4 mmol L-1 P > fluvo-aquic with 1.6 mmol L-1 P > red soil with 1.6 mmol L-1 P. For the two P treatments P release from the paddy soils in the first extraction was 44.3% and 45.6% of total released P, respectively, which were higher than those from red and fluvo-aquic soils. The ratio of P release at the end of release time was 14.0% and 13.1% in the paddy soil treated with 1.6 and 2.4 mmol L-1 P, respectively, but only 5.1% and 9.2% in the red soil and 7.0% and 5.2% in the fluvo-aquic soil, respectively. Comparison of the coefficients of determination (R2) indicated that ET, TC, and PD equations could describe the P release data better than Z, F, and S equations.
LI Shou-Tian ZHOU Jian-Min WANG Huo-Yan DU Chang-Wen CHEN Xiao-Qin
Dynamic changes of soil pH as influenced by ammonium sulfate (AS),monocalciuin phosphate (MCP), potassium chloride (KCl) and their interaction in soils were evaluatedin incubation experiments. Applying these fertilizers significantly reduced soil pH values in allcases and followed sequences of AS > MCP > KCl, MCP > KCl > AS and KCl > AS > MCP for the paddy,calcareous and red soils, respectively. The AS-induced reduction of pH in the three soils followedthe sequence of red soil > paddy soil > calcareous soil, while in MCP and KCl systems the reductionof pH followed the sequences of calcareous soil > paddy soil > red soil and red soil > calcareoussoil > paddy soil, respectively. The interactions of the NPK fertilizers on pH were significant. MCPplus KCl or MCP plus AS reduced pH values more than the fertilizers applied solely in the paddysoil, but AS partly counteracted the effect of MCP on pH in the 1 d sample of the calcareous soil.The effect of MCP on pH was trivial when MCP was applied in combination with KCl or AS in the redsoil. When applied in combination with AS, KCl did not affect soil pH initially, but suppressed thereduction of pH at the later incubation stage, which was related to inhibition of nitrification byKCl in the soils.
WANG HUOYAN, ZHOU JIANMIN, CHEN XIAOQIN, LI SHOUTIAN, DU CHANGWEN and DONG CAIXIAInstitute of Soil Science, the Chinese Academy of Sciences, Nanjing 210008 (China)
