Phosphorus availability of seven organic manures in a sandy soil

Nitrogen is the main limiting factor of plant production in the Bonaerense Valley of the Colorado River, Argentina (VBRC). However, organic fertilizer application based on N requirements often results in unbalances of other nutrients, such as phosphorus, which can result in contamination problems. Therefore, it is necessary to know the amount of P provided by the organic amendments and its availability to establish management strategies that minimize environmental impacts. A field mineralization assay was performed during the spring-summer period 2013/14 in the VBRC. The amendments used were: BioOrganutsa (commercial amendment, B) vermicompost of municipal solid waste (WC), composted poultry manure (CPM), horse manure (HM), poultry manure (PM), cattle manure (CM) and sheep manure (SM). The amount of each amendment was adjusted to 350 kg N ha(-1). Each treatment was sampled at 0, 3, 21, 35, 49 and 83 days. The extractable P (Pe) was determined for each sample. Linear regression and curve comparison analysis were used in order to evaluate Pe dynamics during incubations. All the evaluated amendments provided more P than the crop requirement. However, two different behaviors were observed in P availability during the incubations (p-value <0.05). B, PM and SM showed an initial contribution of Pe that remained stable for the evaluated period, while PMC, HM, CM and WC showed a progressive increase of Pe during incubation (p-value <0.05).