Soil moisture availability and use by cover crops are the dominant concerns in dryland production systems.Yet more and more innovators are finding that carefully managed and selected cover crops in their rotations result in increased soil moisture availability to their cash crops. They are finding ways to incorporate cover crops into flexible rota- tions that can be modified to capitalize on soil moisture when available while preventing adverse effects on cash crops. This delicate bal- ance between water use by the cover crop and water conservation—particularly in conservation tillage systems—will dictate, in part, how cover crops work in your rotation. See also Managing
Cover Crops in Conservation Tillage Systems
(p. 44).
Perennial legumes provide numerous benefits to grain cropping systems in the Northern Plains, including increased grain yield, nutrient scaveng- ing, carbon sequestration, breaking weed and insects cycles and for use as feed (129).
Cover crop features: perennial medics persist due to hard seed (of concern in some systems),
providing green manure and erosion control;
field peas and lentils (grain legumes) are shal-
low-rooted yet produce crops and additional N in years of good rainfall.
An excellent resource describing these rota- tions in detail is Cereal-Legume Cropping
Systems: Nine Farm Case Studies in the Dryland Northern Plains, Canadian Prairies and Intermountain Northwest (258).
7 to 13 Years: Flax>Winter Wheat>Spring Barley>Buckwheat>Spring Wheat>Winter Wheat>Alfalfa (up to 6 years) >Fallow
System sequences are:
• Flax or other spring crops (buckwheat, wheat, barley) are followed by fall-seeded wheat (sometimes rye), harvested in July, leaving stubble over the winter;
• Spring-seeded barley or oats, harvested in August, leaving stubble over the winter; • Buckwheat, seeded in June and harvested in
October, helps to control weeds;
• A spring small grain, which outcompetes any volunteer buckwheat (alternately, fall-seeded wheat, or fall-seeded sweetclover for seed or hay).
The rotation closes with up to 6 years of alfalfa, plowdown of sweetclover seeded with the previ- ous year’s wheat or an annual legume green manure such as Austrian winter peas or berseem clover.
There are many points during this rotation where a different cash crop or cover crop can be substituted, particularly in response to market conditions. Furthermore, with cattle on the ranch, many of the crops can be grazed or cut for hay.
Moving into areas with more than 12 inches of rain a year opens additional windows for incor- porating cover crops into dryland systems.
9 Year: Winter Wheat>Spring Wheat> Spring Grain/Legume Interseed>Legume Green Manure/Fallow>Winter Wheat> Spring Wheat>Grain/Legume Interseed> Legume> Legume. In this rotation, one year of
winter wheat and two years of spring-seeded crops follow a two or three-year legume break. Each legume sequence ends with an early sum- mer incorporation of the legume to save moisture followed by minimal surface tillage to control weeds. Deep-rooted winter wheat follows sweet- clover, which can leave surface soil layers fairly dry. Spring-seeded grains prevent weeds that show up with successive winter grain cycles and have shallower roots that allow soil moisture to build up deeper in the profile.
In the second spring-grain year, using a low-N demanding crop such as kamut wheat reduces the risk of N-deficiency. Sweetclover seeded with the kamut provides regrowth the next spring that helps to take up enough soil water to prevent saline seep. Black medic, INDIANHEAD lentils and field peas are water-efficient substitutes for the deep-rooted—and water hungry—alfalfa and sweetclover. These peas and lentils are spring- sown, providing back-up N production if the for- age legumes fail to establish.
While moisture levels fluctuate critically from year to year in dryland systems,N levels tend to be more stable than in the hot, humid South, and adding crop residue builds up soil organic matter more easily. Careful management of low-water use cover crops can minimize soil water loss while adding organic matter and N. Consequently, dry- land rotations can have a significant impact on soils and the field environment when used over a number of years.
These improved soils have higher organic mat- ter, a crumbly structure, and good water retention and infiltration. They also resist compaction and effectively cycle nutrients from residue to subse- quent crops.
Remember, the benefits of cover crops accrue over several years. You will see improvements in crop yield, pest management and soil tilth if you commit to cover crop use whenever and wherev- er possible in your rotations.
INTRODUCTION
Conservation tillage is defined as a system that leaves enough crop residue on the soil surface after planting to provide 30% soil cover, the amount needed to reduce erosion below toler- ance levels (SSSA). Today, however, most conser- vation tillage practitioners aim for greater soil cover because of additional benefits of crop residue. Cover crops are critical to producing this residue and have the potential to maximize con- servation tillage benefits.
Benefits of conservation tillage systems include: • reduced soil erosion
• decreased labor and energy inputs
• increased availability of water for crop production • improved soil quality
Cover crops further benefit conservation tillage
systems by:
• producing crop residues that increase soil organic matter and help control weeds • improving soil structure and increasing infiltration • protecting the soil surface and dissipating rain-
drop energy
• reducing the velocity of water moving over the soil surface
• anchoring soil and adding carbon deep in the soil profile (via roots)
Conservation tillage has been adopted on more and more acres since the 1970’s thanks to improvements in equipment, herbicides and other technologies. Several long-term, incremen- tal benefits of conservation tillage have emerged. The most important benefits have been attributed to the accumulation of organic matter at the soil surface.
This accumulation of surface organic matter results in:
• increased aggregate stability, which helps to increase soil water infiltration and resist erosion • improved nutrient cycling and water quality,
due to keeping nutrients in the field
• increased biological activity, which improves nutrient cycling and can influence diseases and pests
Additional benefits from conservation tillage sys- tems compared to intensive or conventional