Feasibility of integrating annual feed grains into established organic pasture

Dairy farmers in New England are looking for ways to (1) reduce the need for imported grain and (2) minimize the impacts that their operations have on the environment. They have also identified weed control as one of their most challenging management issues. Intercropping annual feed grains with perennial pasture could reduce the need for grain imports and intensive tillage for weed management, and may lessen ecosystem disservices from dairy production and the need for purchased off-farm inputs. This experiment investigated different approaches to establishing annual feed grains into a perennial pasture community to identify optimal combinations of tillage and perennial pasture community suppression that effectively balance weed pressure and grain production. A six-treatment experiment was piloted in 2012 at the UNH Organic Dairy Research Farm in Lee, NH. In 2013, the experiment was expanded and established as a corn-soybean rotation at the UNH Kingman Research Farm in Madbury, NH. At the Kingman Farm, we established nine cropping system treatments, each replicated four times in a randomized complete block design. Our cropping system treatments spanned two disturbance intensity gradients allowing us to explore ecosystem service tradeoffs associated with low external input annual grain crop production. In 2013, corn grain yields averaged 4.8 and 5.6 Mg ha^-1 in the best performing treatments (a conventionally managed strip-tillage system and an organically managed full-tillage system, respectively). Grain yield was affected more by the method of perennial pasture community suppression than by the method of seedbed preparation and was highest where the perennial community was completely eliminated either via herbicide or full tillage. Weed abundance appears to be an emerging tradeoff associated with intense soil disturbance. These results illustrate the important link between soil disturbance and weed abundance in agroecosystems. These results also suggest that pasture recovery following intercropping with feed grains can be improved by implementing minimum tillage approaches to feed grain establishment.    

Introduction:

According to the 2009 USDA Economic Research Service Report Summary, small organic dairy farms (fewer than 70 cows) in the Northeast and upper Midwest make up over 80% of the organic dairy operations in the U.S., and rely more on pasture feed than the predominantly grain-fed organic dairy operations of the west. While a pasture-based system is less expensive than purchasing feed quality grains, the output (cwt milk per cow) is significantly diminished, and labor requirements are more intense when compared to con?ning cows and feeding harvested forages, making small, pasture-based dairy operations less profitable (McBride and Greene, 2009). This model incentivizes increasing the scale of organic dairy operations at the cost of the ecosystem services typically generated in closed-loop farming operations. 

Due to the short growing season, dairy farmers in the Northeast must purchase between 25 and 50% of their winter feed (Maltby, 2012). The cost of feed grains has more than doubled since 2005 and is projected to continue the climb. This escalation in the cost of feed grain only decreases profitability for farmers, threatening the survival of small dairy farming operations (Maltby, 2012). By incorporating annual feed grains into pastureland, farmers may be able to produce a percentage of their winter dairy grain needs, thereby increasing productivity of their pastureland and decreasing the overall costs of inputs.  

Organic feed grain production often requires frequent tillage to prepare seed beds and suppress weed growth (Smith et al., 2010). Conventional tillage can damage soil structure and can result in a loss of soil organic matter, reducing water holding capacity, and increasing the risk of soil erosion (Lal, 2004). Intercropping could reduce the need for inter-row cultivation for weed control and if grains are intercropped with legumes could reduce the need for supplemental nitrogen (Hauggaard-Nielsen et al. 2008).

Minimizing off-farm inputs such as fertilizer not only reduces environmental contaminates (such as nitrate and trace gas emissions) but also capital costs to farmers. In 2010 U.S. farmers spent 21 million dollars on fertilizers (including lime and soil conditioners) (USDA NASS 2012). One potential approach to increasing the efficiency of nitrogen cycling and reducing trace gas emissions in agricultural systems is to reduce tillage in conjunction with the maintenance of perennial ground cover (Robertson and Vitousek, 2009). Reduced tillage, however, particularly in organic cropping systems, can result in increased weed populations which can ultimately reduce crop yields (Smith et al., 2010). Therefore, identifying intercropping systems that effectively balance soil disturbance with the maintenance of perennial cover so as to effectively cycle nutrients, build soil organic matter, and reduce erosion potential, is a priority for organic research.

We sought to answer the following questions: What combination of practices maximizes provisioning ecosystem services (e.g., grain yield)? What are the tradeoffs associated with annual-perennial intercropping, and can these be minimized? How do these tradeoffs manifest over the longer-term? By incorporating annual feed grains into perennial pasture systems, we expect to expand production operations within organic dairy systems. In addition to enhancing overall system productivity, reducing costs and increasing net farm income, an integrated dairy forage operation may also improve soil quality relative to a conventionally-tilled system, which would contribute to improved soil aggregate structure and water holding capacity, off-site water quality, as well as building belowground habitat for soil communities (Kladivko, 2001). The first two years of this project served as the initial stages of a long-term agricultural research experiment. During year one and two, we sought to set the stage for integrating annual feed grains into perennial legume pasture, as well as establish a baseline of inquiry for a variety of future research questions. 

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