Po In Soil Research Articles

Labile, organic phosphorus in incubated soils estimated by macroporous anion‐exchange resin

Abstract Information on the organically‐bound phosphorus (Po) in soil and particularly the labile Po, the part which is most accessible for mineralization, is scarce and contradictory partly because of a lack of suitable methods. A newly developed method for estimating labile Po in soil by extraction with macroporous anion‐exchange resin was tested and compared with the Hedley‐fractionation method on two sandy loams, an old permanent pasture and a neighbouring, arable field. Treatments expected to either build up or reduce soil labile Po, and included variation of soil moisture and temperature, additions of cellulose and inorganic nitrogen (N), P and potassium (K), addition of lime, and pre‐depletion of inorganic P (Pi) with gel‐type anion‐exchange resin. The macroporous resin method extracted more Po from the pasture soil than from the arable one. The level was in accordance with turnover rates of Po under natural conditions. The way the resin‐extracted Po reacted to the treatments came up to our expecta...

Effect of tillage and fertilization on inorganic and organic soil phosphorus

This study was conducted to evaluate the impact of tillage and fertilization practices on soil organic carbon (organic-C) and the distribution of phosphorus between inorganic (Pi) and organic (Po) pools in a clay and sandy loam soil under a continuous corn (Zea mays L.) production 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 June 1988. Treatments consisted of three types of tillage: (i) conventional (CT): fall moldboard ploughing with two spring diskings; (ii) reduced (RT): with either fall chisel ploughing (1981–1986) or no fall tillage (1987) followed by one spring disking, and (iii) no-till (NT); and two types of fertilization (i) inorganic (I): 170 kg N ha−1. 80 kg P2O5, ha−1, 75 kg K2O ha−1, and (ii) organic fertilizer (O): dairy manure 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 1985, soil pH was significantly lower in the I fertilizer treatments. Reduction of tillage intensity resulted in a lower pH in the surface layer 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. Moderately labile Po levels were not affected by treatments in the clay soil. In the sandy loam soil, O fertilization decreased moderately labile Po levels in the surface layer of the NT treatment, and increased this P fraction in the 10- to 20-cm soil layer of the RT and CT treatments. In the surface layer of both soils, labile levels of Pi were greater for the O fertilization treatment (approximately 40 and 47% higher for the clay and sandy loam, respectively), and were lower under CT. Increased labile Pi levels were associated with the O fertilizer treatment in the 10- to 20-cm depth increment in the sandy loam soil only, suggesting a greater downward movement of P with manure applications. Key words: Conventional tillage, zero-tilled, no-till, reduced tillage, manure, P fractionation