CROPS AND SOILS

Effect of Organic Materials on Phosphorus Sorption and Availability to Phaseolus Vulgaris in an Andic Eutropept in Costa Rica: Evaluation of Fresh Biomass, Compost and Manure

Presented by

Karen L. Lowell
Ph.D Candidate, Crop & Soil Sciences

Tuesday, March 14, 2000
2:00 - 3:00 PM
(Note time change)
135 Emerson Hall

Abstract

A series of greenhouse and field experiments was carried out in an Andic Eutropept in Turrialba, Costa Rica to evaluate the effect of two types of compost, cow manure and fresh biomass (Erythrina poeppigiana, Calliandra calothyrsus, Gliricidia sepium and Arachis pintoi) on availability and sorption of phosphorus (P) in soils amended with these materials. Anion exchange resin membranes (AEM) were used to measure P availability in the soil, and both Langmuir sorption isotherms and a single point sorption capacity (New Zealand P (NZP)) were calculated to assess the effect of the materials on P sorption. Water-soluble inorganic and organic P, and dissolved organic carbon were measured in distilled water extracts of the materials. Total P of the materials was also determined. OM amended soils showed higher levels of AEM P and P uptake in a greenhouse study with beans (Phaseolus vulgaris) than unamended soils. Fertilizer rates may be cut in half without noticeable decline in availability or uptake measures when TSP is combined with OM in a buried layer. Buried placement allows the OM and TSP to remain in close contact without significant mixing with the soil. Soluble inorganic P is a better indicator the effect of OM on AEM P or P uptake in the short term, but total P content of the materials is a better predictor of available P over the longer term. Phosphorus uptake by beans increased as NZP decreased. In a greenhouse study NZP sorption capacity was significantly lower in soils mixed with cow manure, compost or bocashi. The Langmuir sorption maximum calculated for the same soils failed to show significant treatment differences. When OM was applied as a concentrated layer in the soil profile, soil below the OM layer failed to show a significant decrease in P sorption by either sorption measure. Mulches of the fresh biomass did not decrease NZP in the top 0.5 cm of soil in a field study. Soluble inorganic P was the best indicator of the effect of a given OM on P sorption.