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Management and Environmental Factors Affecting Nitrogen Cycling and Use Efficiency in Forage-Based Livestock Production Systems

Principal Investigator/Project Leader: 
Department of Project: 
Stockbridge School of Agriculture
Project Description: 

This work will focus on both nitrogen management and grazing management to maximize sustainability and profitability. For example, the addition of legumes in pasture provide a free source of nitrogen to companion grasses while simultaneously enhancing feed quality. While it is known that legumes can reduce or eliminate the need for supplemental nitrogen fertility, these dynamics are not well studied in the specific context of stockpiling. Stockpiling avoids late summer grazing in order to create a reserve for October-December grazing. During this period, plants begin the cold acclimation process and biological activity – necessary for nitrogen fixation – can slow. We will investigate the ability of legumes to provide nitrogen needs to companion grasses for the specific purpose of stockpiling. If successful, we can reduce nitrogen inputs, which come with both an environmental and economic cost. Concurrently, we can extend the grazing season which delays the need to utilize dry hay reserves and minimizes the amount of hay that must be produced. Reducing reliance on hay reduces associated labor and fossil fuel necessary for making and harvesting hay.

We will also study the associated ammonia volatilization from the manure of animals fed different hay and legume rations and their final nutrient content. Feed can affect manure composition and create variation in the efficiency of manure as supplemental fertility. This manure assessment allows for greater understanding of nitrogen cycling in systems as a factor of forage composition.

Greenhouse experiments will investigate the regrowth behavior of pasture grasses following defoliation events that will mimic different grazing heights. The effects of supplemental nitrogen as well as residual height – and their effects on photosynthesis and associated physiology – will demonstrate the importance of grazing management. Overgrazing has been generally shown to reduce the rate of regrowth and plant vigor. Nitrogen fertilizer is often applied to support regrowth, but is commonly believed it will compensate for over grazing. Improving our understanding of the relationship between nitrogen and grazing height on regrowth and plant physiology can make better use of fertility and inform conscienctious management practices. Demonstrating the effects on physiology, such as carbon assimilation, can also predict how these management practices can hinder or support carbon sequestration or how plants may respond to stress events such as variations to heat or water availability.

Agriculture topics: 
Crop and Cropping System
Field Crops
Forage and Grazing
Manure and Nutrient Management
Soil and Nutrient Management
Soil Health