EFFECT OF TILLAGE AND FERTILIZATION ON INORGANIC AND ORGANIC SOIL-PHOSPHORUS

This study was conducted to evaluate the impact of tillage and fertili zation practices on soil organic carbon (organic-C) and the distributi on of phosphorus between inorganic (Pi) and organic (Po) pools in a cl ay and sandy loam soil under a continuous corn (Zea mays L.) productio n system. Tillage treatments were established in the fall of 1981. The soils for this study were sampled (0- to 10-cm and 10- to 20-cm) in J une 1988. Treatments consisted of three types of tillage: (i) conventi onal (CT): fall moldboard ploughing with two spring diskings; (ii) red uced (RT): with either fall chisel ploughing (1981-1986) or no fall ti llage (1987) followed by one spring disking. and (iii) no-till (NT): a nd two types of fertilization (i) inorganic (1): 170 kg N ha-1, 80 kg P2O5 ha-1, 75 kg, K2O ha-1, and (ii) organic fertilizer (0): dairy man ure applied to give 170 kg N ha-1 plus 80 kg P2O5 ha-1 from inorganic P fertilizer. Even though a lime application was made in the fall of 1 985. soil pH was significantly lower in the I fertilizer treatments. R eduction of tillage intensity resulted in a lower pH in the surface la yer of the sandy loam soil. Tillage did not affect soil organic-C. or total soil Po (soil-Po) in either soil. Compared with the I fertilizer treatment, the O fertilizer treatment resulted in increased levels of soil organic-C and soil-Po only in the sandy loam soil. Labile levels of Po in the soil were not affected by treatments. Increased soil-Po levels possibly resulted from an increase in stable Po complexes. Mode rately labile Po levels were not affected by treatments in the clay so il, in the sandy loam soil. 0 fertilization decreased moderately labil e Po levels in the surface layer of the NT treatment. and increased th is P fraction in the 10- to 20-cm soil layer of the RT and CT treatmen ts. In the surface layer of both soils. labile levels of Pi were great er for the 0 fertilization treatment (approximately 40 and 47% higher for the clay and sandy loam, respectively), and were lower under CT. I ncreased labile Pi levels were associated with the 0 fertilizer treatm ent in the 10- to 20-cm depth increment in the sandy loam soil only. s uggesting a greater downward movement of P with manure applications.