Evaluating Organic Land Management Techniques to Meet Energetic Demands of Wintering Waterbirds
August 2010 - December 2013
- Region 2
In the last century, the Rocky Mountain population of sandhill cranes (Grus canadensis tabida) has shifted its primary wintering grounds from central Mexico to the Middle Rio Grande Valley (MRGV) of New Mexico. Decreased habitat availability in Mexico and a growing agricultural community in the MRGV that inadvertently provides foraging material has contributed to a more northerly terminal wintering area. This shift has led to substantial yield losses on private lands from depredation. Furthermore, there are limited areas along the MRGV that provide a protected roosting and foraging area for the sandhill crane. Primarily this role belongs to the state run Ladd S. Gordan Waterfowl Mangament Area (LGWMA) and Bosque del Apache National Wildlife Refuge (BdANWR) south of San Antonio, New Mexico. In order to encourage the spatial distribution of cranes along the MRGV, and provide for their energetic wintering needs LGWMA and BdANWR have agreed to share the role of producing high energy, carbohydrate foods that provide for the estimated 30,000 sandhill cranes that winter in the MRGV. The Bosque del Apache NWR, located within the floodplain of the Rio Grande River, uses an integrated management scheme of moist-soil plant production (or moist-soil management) and traditional agriculture to meet these energetic needs. Moist-soil management (MSMGT) can be defined as the creation of exposed, saturated soil in wetlands by irrigation or drawdown during the growing season to promote germination, growth, and seed production of plants on mudflats (Haukos and Smith, 1993). At BdANWR, refuge managers manipulate soils, hydrology, and vegetation succession to stimulate the germination of high energy wetland plants. These active practices seek to provide similar functional results of stochastic events such as landscape scouring, nutrient renewal, and soil disturbance that would have transpired during natural flooding events of the Rio Grande prior to European settlement and as a result, subject soils under MSMGT to a reduced tillage regime and high organic residual input that builds soil nutritional properties. However, many MSMGT units on the refuge face annual problems with soil salinity, and yield reductions in desirable wetlands plants coincide when salinization of the rhizosphere occurs. This salinization could be a result of improper water management practices that fail to effectively leach salts down the profile (Hillel, 2000). In addition to evaluating the effects of current moist soil management practices on soil properties, information is needed to determine whether modified moist soil management practices could enhance soil properties and facilitate an integrated moist-soil / agricultural rotation that would enhance production of agricultural crops through natural wetland soil processes. The refuge uses traditional agricultural practices to produce field corn (Zea mays) which provides an additional rich carbohydrate food source to supplement moist-soil seed production and a means of manipulating the distribution and local population densities of sandhill cranes and snow geese to minimize cholera outbreaks. Sandhill cranes have been described as omnivorous and opportunistic feeders (Guthery 1976, Mullins and Bizeau 1978) and while corn does not satisfy the complete set of nutritional requirements needed in their life history, studies have documented where corn, when available, makes up 97% of a crane’s total diet (Reinecke and Krapu 1986). Currently the refuge uses a cooperative farming agreement with local farmers to produce 1,000 tons of corn per year. The cooperative farming program rotates agricultural fields between alfalfa (Medicago sativa) and field corn where alfalfa is harvested as a cash crop and grain corn is left in the fields as forage for cranes and snow geese (Chen caerulescens). In recent years, however, corn production has dropped precipitously from 907,185 Kg in 2006 to only 9,072 Kg in 2009, possibly due to decreased soil fertility from intensive tillage, salt laden irrigation water leading to increased salinity in the rhizosphere, and resilient nematode parasites. These types of agricultural tillage regimes promote the release and subsequent degradation of previously protected organic matter, contributing to long-term decreases in soil microbial biomass and organic matter as well as diminishing the capacity of the soil to retain nitrogen (Calderon & Jackson, 2001). Furthermore, parasitic nematodes seem to persist through alfalfa rotations leaving corn highly susceptible to depredation. Sustained flooding has shown some success in the reduction and eradication of nematodes (Brown, 1933) (Brown and Kerry, 1987) by reducing the amount of oxygen available for respiration and increasing concentrations of substances toxic to nematodes such as organic acids, methane, and hydrogen sulfide (MacGuidwin 1993). However the success of this technique is related to the timing and duration of flooding and its ability to coincide with the life history of the crop being produced. Overall, these decreased levels of corn production may be insufficient to maintain healthy body conditions for migratory birds which may reduce breeding productivity and increase susceptibility to avian cholera. Therefore, the refuge is considering alternatives for the future of its agricultural program. Specifically, the goal of the refuge is to develop more sustainable moist-soil and agricultural practices that are functional without genetically modified crops (GMC), minimize the use of fertilizer and chemical inputs, and are based on a more integrated understanding of soil-system processes. We speculate that an integrated moist-soil and agricultural management scheme will reduce the impacts of tillage on soil systems, enhance soil nutrient, soil structure, and reduce soil salinity allowing for the proper conditions to successfully grow non-GMO corn. Historically, USFWS has been hesitant to support the use of GMCs, specifically modified corn that contains Bacillus thuringiensis to control detrimental pests because of its overall reduction of invertebrates, especially Lepidoptera. These reductions could have impacts on the trophic cascade, impacting forage availability for obligate species like neotropical migrants and bats (Chiroptera). Additionally, from the standpoint of the refuge, it is currently difficult to find varieties of corn that do not contain some level of genetic modification and varieties that are available are extremely expensive. Therefore the refuge would need to develop a seed harvesting program in order to become self-sufficient and thus avoid paying high premiums for non-GMO seed. OBJECTIVES: The long-term objective of this study and others are to develop a sustainable agricultural system for Bosque del Apache NWR that is founded on soil ecology, organic farming, and wetland/crop rotations that enhance soil fertility and minimize chemical fertilizer and herbicides and pesticides. The specific objectives of the research to be conducted from October 1, 2011 to September 30, 2012 are to evaluate the abiotic processes and management practices that contribute to a successful sustainable agricultural system. We will: 1) Assess the soil physical, biological, and nutritional suitability of moist-soil managed units to support agricultural crops. 2) Evaluate the effects of winter and spring flooding in agricultural fields to reduce parasitic nematodes. 3) Evaluate the effects of tillage and frequency of irrigation in moist-soil units on soil salinization in the rhizosphere.