Nutrient management under grazing

Abstract

This chapter reviews nutrient management of intensively managed grasslands used for dairy farming in The Netherlands, with emphasis on research but with linkages to practice. Firstly, it provides an overview of the changes that have taken place in nutrient management research and practice during the 20th century. Secondly, it presents the current concept of nutrient management with application to grazed grassland. Finally, it discusses nitrogen (N) management of pastures and the tools to improve N management at operational level. Nutrient management under grazing has evolved from merely optimizing manure and fertilizer applications for high herbage yield towards improving nutrient use efficiency at farm level whilst maintaining productivity. Nutrient management under grazing is highly complex, because of the uneven distributions of nutrients in pastures, the difference in nutrient element requirements for herbage growth and dairy production, and the difference in mobility between nutrients and the tendency of especially N to escape from the system. Furthermore, boundary conditions of nutrient management in practice change frequently due to changes in manure policy. The economic costs of nutrients in dairy farms have decreased during the 20th century, but the time and costs associated with nutrient management in practice have increased, mainly because of the manure policy. Nutrient balance sheets have greatly contributed to increased understanding of nutrient cycling and nutrient management in dairy farming, as they provide guidance to improving nutrient use efficiency. Emphasis in nutrient management under grazing has been on N and to a much lesser extent on P, K and Mg. The emphasis on N follows from its impact on productivity and the environment. In the near future, there will be increasing attention also for P and micro-nutrients like copper and zinc as they tend to accumulate in intensively managed grassland soils to levels critical for the environment and animal and human health