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 tolerance levels (SSSA). Today, however, most conservation tillage practitioners aim for greater soil cover because of additional benefits of crop residue. Cover crops are citical to producing this residue and have the potential to maximize tillage benefits.
- reduced soil erosion
- decreased labor and energy inputs
- increased availability of water for crop protection
- improved soil quality
Cover crop benefit conservation tillage systems by:
- producing crop residue that increase soil organic matter and help control weeds
- improving soil structure and increasing infiltration
- protecting the soil surface and sissipating raindrop energy
- reducing the velocity of water moving over the soil surface
- anchoring soil and adding carbon deep in the soil profile
Accumulation of surface organic matter results in:
- increased aggregate stability, which helps to increase soil water infiltration and resist in 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 systems compared to intensive or conventional tillage systems:
- reduced labor and time -- one or two trips to prepare land and plant compared to three or more reduces labor and fuel costs by 50% or more
- reduced machinery wear -- fewers trips means fewer repairs
- increased wildlife -- crop resideues provide shelter and food for wildlife, such as game birds and small animals, which can results in additional farm revenue
- improve air quality -- by reducing win erosion (amount of dust in the air), fossil fuel emissions from tractors (fewer trips) and release of carbon dioxide into the atmosphere (tillage stimulates the release of carbon from organic matter)
Cover crop biomass is a source of organic matter that stimulates soil biological activity. Soil organic matter and cover crop residues improve soil physical properties, resulting in:
- greater water infiltration, due to direct effects of the residue coverage or to changes in soil structure
- greater soil aggregation or titlh, resulting in better nutrient and moisture management
- less surface sealing, because residue intercepts rain drops, reducing the dispersal of clay particles during a rainfall or irrigation event
- greater soil porosity, due to the macropores that are formed as roots die and decompose
Cover crops and conservation tillage combine to reduce soil erosion and win erosion.
Crop rotation provides numerous benefits to any cropping system. It is critical to reducing the incidence of diseases and pests, and is also credited with improving nutrient use and reducing weeds. Cover crops increase the complexity and intensity of crop rotations, effectively increasing crop rotation benefits.
Economics of cover crop establishment and use
Using cover crops in any tillage system usually costs more time and money than not using cover crops. Depending on your particular system, you may or ay not be repaid for your investment over the short term, If you are already using cover crops but are considering switching to conservation tilalge, the economics are similar to using cover crops in conventional tillage systems, but the benefits may be expressed more in the conservation system.
Factors affecting the economics of cover crop use include:
- cash crop grown
- cover crop selected
- time and method of establishment
- method of termination
- cash value applied to the environment, soil productivity and soil protection benefits derived from the cover crop
- cost of nitrogen fertilizer and the fertilizer value of the cover crop
- cost of fuel
Plant cover crops on time
In order to maximize benefits -- or to work at all -- cover crops need to be planted early, sometimes before the summer crop is harvested. Timely planting results in:
- good root establishment and topgrowth before the crops go dormant
- reduced chance of winter kill
- more biomass production compared to later planting dates
- greater uptake of residual soil N
Cover crops in conservation tillage systems are usually planted with a drill or broadcast on the soil surface, but several alternate methods can be used. Good soil-seed contact is required for germination and emergence. Most small seeded legumes require shallow seed placement (1/4"), while larger seeded legumes and small grains are generally planted up to 1.5" deep (See Charts).
- Conservation Tillage Drills can handle residue and provide uniform seeding depth and adequate seed-soil contact, even wtih small seeded cover crops. In some situations, preplant tillage can be used to control weeds and disrupt insect and disease life cycles.
- Broadcast seeding requires an increase in the seeding rate compared to other methods (See Charts). Broadcasting is often the least successful seeding method. Small-seeded species such as clovers tend to establish better by broadcasting than larger seed species. A drop-type or cyclone-type seeder can be used on small acreage and provides a uniform distribution of seed. Conventional drills work adequately in some conservation tillage systems--depending on the amount of residue--and may be more successful than broadcast seeding.
- Aerial Seeding
- Frost-Seeding in colder climates, can be used for some cover crop species