Future food and fiber must be produced on existing agriculture land, with fewer negative impacts on natural resources and the environment than in the past. The timely supply, efficient use, and careful monitoring of nutrients in integrated crop, forage, and tree production systems offer the potential for significantly improving efficiency in plant nutrient use. Farmers, researchers, and other stakeholders need to be more actively involved in the generation and use of the knowledge required for integrated nutrient management. Although science-based agriculture has made major contributions to both the quantity and quality of the global food supply, the rate of yield increase for major food crops has begun to slow in recent years. In many parts of the world, agricultural production increases have been accompanied by significant degradation of natural resources, including nutrient depletion on agricultural lands. Integrated nutrient management (INM) is an approach that involves the management of both organic and inorganic plant nutrients for optimal production of cultivated crops, forage, Â  |
 and tree species, while conserving the natural resource base essential for long-term sustainability. Nutrient flows occur at different scales in any agroecosystem, and soil nutrient budgets for a given area and time can be calculated by the difference between the nutrient inputs and outputs (figure 4.3). Large soil nutrient surpluses can lead to environmental pollution, whereas persistent soil nutrient deficits usually indicate nutrient mining. Effective INM involves four interrelated strategies: Conservation and efficient use of native soil nutrients. Conservation practices help to reduce loss of nutrients from agroecosystems due to surface water flows and from erosion of soil by wind and water. Vegetative barriers minimize off-farm transport of dissolved nutrients, dust, and sediments, and deep-rooted plants act as nutrient safety nets, intercepting leached nutrients from the root zone and returning them to the soil surface via litter fall, mulch, or as green manure. In general, conserving existing nutrient resources is easier and cheaper than replenishing and rehabilitating degraded resources. Recycling of organic nutrient flows. Returning crop residues and/or animal manure to cropland is important for system sustainability. Composting crop residues and animal manures enhances the utilization efficiency of easily lost nutrients such as nitrogen. Converting linear flows (lost from the system) of organic nutrients to cyclical flows (returned to the system) can reduce the need for external nutrient inputs. There are related potential price benefits in organic product markets. Livestock are important for processing crop residues, adding value to farm outputs, improving labor efficiency, and providing manure.     
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