Nitrogen balance at the plot scale in grazed pastures.

摘要

The determination of the annual nitrogen balance in a pasture considers the 'plot + animal' system as a single entity. Inputs of mineral and organic fertilizers, complementary feeds, symbiotic fixation and atmospheric deposition of N, are taken intoaccount. Outputs are animal products, harvested herbage, and animal returns outside the plot. The balance surplus includes four items: losses by leaching, gaseous losses, soil nitrogen variation, and cumulated errors origins from the assessment of the various factors. The data necessary for the calculation are explained in detail. This balance was used on a set of experimental farms in Western France. The levels of inputs and of outputs, and the calculated balance surpluses are presented in relation tograssland utilization and pedoclimatic conditions. The relationship between nitrogen balance and nitrate leaching was investigated. The use of this balance calculation as a guide for pasture management or as an indicator for pollution risk, is discussed.