Author
 |
Russelle, Michael |
|
Submitted to: International Symposium on Animal Production
Publication Type: Proceedings Publication Acceptance Date: 11/4/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Nutrients, like nitrogen, phosphorus, and potassium, move through our ecosystems in a variety of forms. Some forms are desirable, such as agricultural products (including meat, milk, and grains), but others can cause environmental damage and threaten human health (such as nitrate, a form of nitrogen, in drinking water). Sustainable management of grasslands sand pastures requires efficient nutrient cycling. In addition, the profitability of these animal production systems improves when nutrients are conserved and recycled. In this review paper, I present the pathways through which several nutrient elements move, discuss factors that regulate their flow rate through these pathways, and recommend critical research needs, based on literature primarily from tropical and subtropical areas. Nutrients enter a field by biological nitrogen fixation, atmospheric deposition (as rainfall, dust, or gas), feed supplementation provided to the animals, and fertilization. Losses of nutrients occur in animal products, plant products (hay and silage), gaseous compounds, leaching below the root zone, and surface runoff. Decomposition of dead plant parts is crucially important to nutrient cycling in pastures, and we may be able to improve nutrient recycling by selecting plants through plant breeding programs. There are clear needs for more research on managing pastures to improve economic productivity under low fertility conditions and to improve retention of nutrients under situations with higher fertility and rainfall. We also need to develop incentives to help producers adopt entire packages of improved management practices for optimal economic and environmental benefit, especially for farms in fragile ecosystems. Technical Abstract: Efficient nutrient cycling in grasslands and pastures is necessary for them to be sustainable agricultural ecosystems over the long term. Moreover, conservation and internal reuse of nutrients increases the profitability of these animal production enterprises. In this paper, I present the pathways through which several nutrient elements move, discuss factors that regulate etheir flow rate through these pathways, and recommend critical research needs, based on literature primarily from tropical and subtropical areas. Major inputs of nutrients occur via biological dinitrogen fixation, atmospheric deposition, feed supplementation, and fertilization, whereas primary outputs include animal products (e.g., meat, milk, and wool), plant products (hay and silage), gaseous compounds, leaching below the root zone, and runoff. Relatively little plant uptake of some nutrients (e.g., N, S, and P) occurs from urine and dung patches, which represent concentrations of nutrients gathered from broad areas. Litter decomposition is of crucia importance to nutrient cycling, and the impact of this process often is underestimated. Recent findings in Africa and South America suggest that appropriate selection of legume species for polyphenol and N concentration in herbage may improve legume persistence and N supply in pastures, while currently improving N cycling through excreta. Much more research is needed on managing pastures to improve economic productivity under low fertility conditions and to improve retention of nutrients under situations with higher fertility and rainfall. Also needed are incentives to help producers adopt entire packages of improved management for optimal economic and environmental benefit. |
