Ability of a Green Manure Crop to Increase Availability of Organic Phosphorus Fertilizers.
Terry Rick1, Clain Jones, Richard Engel, and Perry Miller2. (1) Land Resources and Environmental Sciences, Montana State University, P.O. Box 173120, Bozeman, MT 59717, (2) 334 Leon Johnson Hall, Montana State University, Montana State University, Box 173120, Bozeman, MT 59717-3120
Maintaining phosphorus (P) fertility represents a challenge for organic producers in the northern Great Plains because of high pH, calcareous soils that limit P availability. Green manure (GM) crops and organic P fertilizers represent two approaches to improve soil P availability. Our objective was to determine the effect of GM crops fertilized with rock phosphate (RP) and bone meal (BM) on P availability to a subsequent wheat crop. During the first phase of a greenhouse study, pots (15 cm diam. X 12.5 cm) were filled with a low soil test P soil (Olsen P = 4 ug P g-1). Buckwheat (Fagopyrum esculentum cv. Mancan), spring pea (Pisum sativum L.), spring wheat (Triticum aestivum cv. Hank) and a non-crop control (or fallow) were fertilized with RP, BM and monocalcium phosphate (MCP) at rates equivalent to 0, 10 and 25 kg ha-1 available P. During the second phase, spring wheat was seeded 3 weeks after GM residue was incorporated. Buckwheat P uptake was enhanced (p=0.05) by all P sources and was able to use the less soluble BM equally as well as the more soluble MCP. In contrast, spring pea P uptake was significantly higher for MCP than RP and BM, indicating it was less effective at utilizing the less soluble organic P sources. P uptake of the wheat crop in the second phase of the study followed the order, fallow>wheat=buckwheat>spring pea. The results of this study indicate that buckwheat has the capacity to increase P availability of less soluble organic P fertilizers and that inclusion of buckwheat may be preferential to spring pea for enhancing P availability in organic farming rotations in the northern Great Plains.