Relationship of ryegrass growth to extractable phosphorus in acidic soil amended with phosphate rock, coal combustion by-product, limestone, and cellulose

An improved management of phosphorus (P) is crucial for increasing crop pro duction and improving environmental quality of acid infertile soils. Labora tory analyses and greenhouse experiments were conducted to evaluate effects of phosphate rock (PR), coal combustion by-product (BP), limestone, and ce llulose application on the relationship between soil test P and crop growth in acidic soil. Application of PR, BP, limestone, and cellulose increased soil pH, exchangeable calcium (Ca) and magnesium (Mg), and extractable P, a nd decreased free aluminum (Al) ion in the acid soil. Addition of BP or lim estone increased P availability efficiency [PAE, mg dry matter yield (DMY) of plant per mg soil extractable P by Olsen-P procedure] and P utilization efficiency (PUE, mg DMY of plant per mg P in the plant). There was signific ant positive correlation between the PAE and BP rates applied alone (r(2)=0 .979. p<0.01) or with either PR (r(2)=0.972, p<0.01) or PR plus cellulose ( r(2)=0.985, p<0.01). The PUE of ryegrass was significantly correlated with BP rates alone (r(2)=0.957, p<0.01) or with either PR (r(2)=0.906, p<0.01) or PR plus limestone (r(2)=0.699). The increase in PAE and PUE of ryegrass caused by BP and limestone reflected more plant root growth from increased availability of Ca and Mg and higher soil pH.