2013 Annual Report
1a.Objectives (from AD-416):
Objective 1: Evaluate land use systems over agricultural landscapes to determine the effects of management and landscape setting on N dynamics. Sub-objective 1-1. Compare N availability in grasslands and organic pasture to more intensively managed land use systems serving dairy and beef livestock production.
Sub-objective 1-2. Compare N availability in organic production to conventional production systems growing alfalfa, corn, soybean, and small grains. Sub-objective 1-3. Develop environmental and economic partial N budgets to compare grasslands, organic and conventional agronomic, and livestock production systems.
Objective 2: Develop and evaluate cropping systems for optimal biomass production that maintain or enhance soil productivity. Sub-objective 2-1. Quantify the effect of conventional and alternative biomass production strategies on soil productivity, measured by changes in soil carbon (C) and N, and total biomass and crop yield. Sub-objective 2-2. Develop energy budgets to compare energy use in biomass production systems and evaluate the use of biomass for bioenergy feedstock versus livestock production.
1b.Approach (from AD-416):
An evaluation of N dynamics including an assessment of availability, defined as mineral N forms available for plant uptake, across cropland, grassland and pasture systems will be conducted. We will evaluate alternatives to a strict C-S rotation, including perennial grasses, an annual grass hybrid, a living mulch and a cover crop, to compare the effectiveness of these strategies to mitigate potential negative impacts of harvest and to provide greater biomass and economic returns.
This project addressed the development of agricultural systems that support the production of crops for consumption and bioenergy while protecting the natural resource base and economic viability of regional farming practices. For Objective 1, on-farm research compared N availability in conventional and organic crop rotations. Due to climatic difficulties, excessive rain or drought, the research project was not completed. For Objective 1, results from long-term research on conventional and organic cropping systems were used to identify alternative crop rotations and management practices capable of effectively reducing long-term yield variation. Complex interrelationships between soil physical, chemical, and biological variables, crop rotations, management practices, and inputs in these cropping systems were statistically modeled. We developed a classification method that can be used to strategically deploy appropriate management practices for a given cropping system or crop rotation to obtain the largest, most stable crop yields. Guidelines useful in identifying causes of yield variation under certain soil conditions and management practices were developed. These guidelines will help researchers, crop consultants, and farmers to use inputs more efficiently, detect true crop responses to management factors, determine trends and understand changes in yield over time, and assess long-term sustainability of alternative cropping systems. For Objective 2, on-station research on perennial-annual rotation strategies tested alternative approaches for their ability to increase soil C yet allow for residue removal as a biomass-energy product. Red clover living mulches had little agronomic value. Winter rye cover crop showed promise as a C replacement as it established better with residue removal. Limited productivity of perennial grasses in three years make it unlikely to be implemented as a three year component to a corn-soybean rotation. For Objectives 1 and 2, an on-farm assessment of annual harvesting and fertilization strategies effects on soil nutrients, establishment and persistence of plant diversity, and harvestable biomass in perennial systems for biomass and/or livestock production was conducted. Soil nutrient contents were not altered by harvest treatment. Fertilization with manure and high levels of inorganic fertilizer increased some measures of phosphorus and influenced distribution of nitrates. Annual harvesting increased biomass production in some years, but also increased prevalence of invasive sweet clover. High levels of fertility had negative effects on plant diversity, primarily causing loss of native prairie clover cover. These results established that diverse perennial biomass plantings can be used to improve ecosystem services, as well as supply sufficient biomass for removal or grazing, with minimal external fertilizer inputs required to maintain productivity.
Conservation strategies improve soil properties under both conventional and organic management. Management strategies that are useful in both conventional and organic farming are needed for increasing sustainability of agricultural systems. However, it is unknown if management strategies interact and function similarly under conventional and organic farming, or if different approaches are needed for these two systems. In a nine-year evaluation of tillage, rotation, and fertility strategies in both systems, ARS researchers at Morris, MN, took measurements of biomass, yields, soil nutrients, microbial biomass and other physical properties. This study showed that reducing tillage for both systems, and increasing crop rotation diversity for conventional systems resulted in soil improvement, particularly from increased microbial biomass carbon, which is an indicator of a healthy soil. In both organic and conventional systems, maintaining the sustainability of agricultural production requires management strategies that provide sufficient organic matter resources to support soil biota and internal cycling and efficient use of nutrients. These findings broadened our knowledge of the effectiveness of management strategies that improve soil health for system level farming practices.
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