Low-Input Legume/Cereal Rotations for the Northern Great Plains/Intermountain Region
1. To develop dryland legume green manure/cereal rotations using prescribed amounts of water.
2. To measure water-use-efficiency of legumes in terms of biomass and N-fixation.
3. To develop a dual-use system of one-year hay and green manure with irrigation.
4. To determine the effects of green manure on soil N mineralization and nitrate distribution.
5. To adapt legume species to agro-climatic zones in the region.
6. To conduct on-farm, field-scale demonstrations of legume/cereal rotations.
7. To teach producers-at-large and agency personnel how to adapt legume/cereal rotations.
Abstract of Results
This was a comprehensive, multi-state research demonstration and extension project with SARE goals. Activities were designed by the participants, including farmers, to provide data needed to devise cropping systems which allow farmers to reduce purchased inputs, diversify crops, and stabilize income while maintaining profitability and enhancing the environment. Research on dryland systems focused on legume green manure as the nitrogen source for small grains under limited water constraints and annual legumes as alternate cash crops.
Research on irrigated systems focused on dual use of legumes for hay (income stability) and re-growth for green manure as the nitrogen source for ensuing small grain crops as well as a non-chemical weed control derived from cutting management. It is gratifying to report that all seven above-stated objectives were achieved, and that their combined results have had a significant, positive impact on regional agriculture.
Our results show that the dryland water resource can be monitored and managed to allow the growth of a green manure crop in lieu of summer fallow while maintaining about the same amount of water for the ensuing small grain crop. Our data shows that annual legumes do vary in water-use-efficiency, both in terms of biomass production and nitrogen-fixation. Austrian winter pea was superior to four other species studied for water-use-efficiency.
Our research on irrigated systems developed a successful dual-use system in which Berseem clover and annual alfalfa are cut twice to yield 2.5 to 3.0 tons of hay/acre with full re-growth used as a green manure to meet the nitrogen needs of the next year's barley crop. The two hay cuttings and/or inclusion of an oat nurse crop constitute non-chemical weed control.
Our data show that legumes took up existing mineralized soil nitrogen, augmented that with nitrogen-fixation and, after incorporation as green manures, mineralization of their nitrogen was dependent on rainfall and/or available soil water during the warm season. As a result, in some instances small amounts of nitrogen were mineralized the first year with greater amounts appearing the second and third years after incorporation.
Over 175 lines representing a total of 36 annual legume species were evaluated for adaptation to the various environments in the region. More than fifty on-farm field-scale demonstrations of legume/cereal rotations were completed during the project. In addition to the participants, hundreds, if not a few thousand, of farmers-at-large and scores of agency personnel were taught the results of our work through our dissemination activities.
The results of the rotational trials are somewhat diverse because of the variability in climatic conditions, soils, and rotations used on these farms. In general, the sustainable rotations (those which had legumes in them) did reasonably well. From an economic point of view the legume rotations were deemed successful if they produced the basic cash crops (wheat and barley) at a cost which was reasonably close to the cost of the historical practices used on these farms. The full benefits of the rotational changes will not show up in the period of a single cropping cycle. Detailed economic analysis on a per site basis are available.
Precipitation use: Annually, three to four million acre-feet of water that now contributes saline seep formation, leaching of nitrates to ground water by percolating below the root zone, runs off the fields or evaporates would be used to grow green manure/cover crops or alternate cash crops.
Annually, about 120,000 tons of synthetic N fertilizer costing about $24 million ($5 to $15 per acre) would be replaced by legume N which would be placed more ideally in the soil, more gradually released for plant uptake and less subject to leaching or becoming a ground water pollutant.
Several hundred thousand to a few million acres damaged annually by erosion, primarily by wind but, also, some by water, would have the erosion damage reduced to tolerable levels. A minimum 5 tons/acre/year reduction is estimated.
Annually, 75,000 to 150,000 tons of seed for green manure, cover and alternate cash crops would be required. Much of this could be produced on-farm for plant back but, a significant portion would be supplied by the seed trade industry. This would be a $50 million industry in this region.
Tractor fuel bills would be reduced from 50 to 80 percent. Estimate to be from $5000 to $50,000 per farm, depending on size.
A few to several hundred farms in the higher rainfall areas would derive the above benefits while maintaining income stability by adopting dual-use legumes (hay and green manure) in their rotations. Barley producers in these areas would achieve maximum economic yield without the use of commercial N fertilizer.
It is estimated that about 2,000 farms have adopted an annual legume in lieu of summer fallow grown in rotation with small grains on an average of 50 acres per farm.
Operational recommendations include:
•Obtain over 150 climatic and soil attributes of their farm from MAPS Mailbox computer program.
•Accurately monitor stored soil water and precipitation on their farm throughout the year.
•Begin adoption of the flexible green manure cropping system by planting an annual legume in lieu of summer fallow on about 100 acres (10% of fallow ground) to learn how and to obtain site specific evaluation.
•Stop using cultivated summer fallow (Black fallow).
•Stop using chem-fallow (Brown fallow).
•Plant about 50 acres of a legume cash seed crop or other alternate cash crop to learn how to grow, harvest, clean, store, and market these crops.
•Diversify cropping pattern to include one or more specialty crops on 10% to 20% of cropland.
•Integrate a livestock (cattle, sheep, or hogs) enterprise with the cash crop enterprises.
Reported in 1995