This practical "how-to guide" provides guidance on using conservation tillage under furrow irrigation to growers, crop consultants, and public sector practitioners. This guide incorporates 4 years of field research done near Fort Collins and years of work done on the Western Slope as well as wisdom and experience of local farmers practicing conservation tillage.
Frequently Asked Questions
Tillage, generally, is defined as those soil-stirring operations performed for the purpose of producing crops. Conservation tillage is an umbrella term that encompasses any tillage and planting system that maintains at least 30% of the soil surface covered by residue following planting, or a system that maintains at least 1,000 pounds per acre of small grain residue on the surface during the critical erosion period.
The use of conventional (or "clean") tillage often results in overtilled soils, which causes the loss of organic matter and the breakdown of soil structure. Clean tillage can also promote soil erosion, create soil compaction, increase soil moisture loss, as well as increase labor and production costs.
There are several benefits of using conservation tillage. Conservation tillage can eliminate field operations, reducing production costs as well as soil compaction. Conservation tillage reduces soil erosion caused by wind and water, making crop production more sustainable. Conservation tillage can reduce the loss of fertile soils and nutrients, maintaining yields. Conservation tillage can have economic benefits to growers. Conservation also has several environmental benefits, such as providing shelter and habitat for wildlife, protecting water quality by reducing the amount of sediment carried downstream to lakes and waterways, and potentially reducing herbicide use due to decreased weed infestations. These environmentally sound cropping methods can have the added benefit of improving public relations with the urban community. Finally, conservation tillage has several benefits specific to furrow irrigation that are discussed below.
Soil water content is often higher when conservation tillage is used compared to clean tillage. In a study in Western Colorado, average soil water content was 17% (for corn and soybeans) to 27% (for dry beans) higher with conservation tillage than with clean tillage. Soil infiltration rates are also much higher (24-50%) with conservation tillage than with clean tillage, according to another study conducted in Western Colorado; that same study showed that advance time (that is, the time it takes irrigation water to move down the furrow) is 25-37% longer with conservation than with clean tillage. Because higher infiltration rates and higher soil water contents occur with conservation tillage, it may be possible to irrigate less often under conservation tillage. This saves not only water, but also the labor needed to irrigate crops.
Managing the bottom of the furrow is important in controlling irrigation water infiltration, as residue in the furrow can increase lateral soil wetting. To acheive acceptable advance times under conservation tillage conditions, it may be necessary to have a slightly larger furrow with a smooth, compact, clod-free bottom. Howeverm ubcreasubg tge furrow stream size too much can create an erosive energy that causes the water to transport residue, which can result in "furrow damming." Damming can be minimized by maintaining residue in as large a size as practical. Just as farmers have learned to balance infiltration time and advance time under clean irrigation in order to furrow irrigate successfully, farmers can learn to balance these factors to successfully furrow irrigate under conservation tillage.
Finally, a conservation tillage system that maintains crop residue on or near the soil surface has been shown to reduce furrow erosion during irrigation, as the soil is more protected from the erosive energy of irrigation water when surface residue is present. In a study conducted in western Colorado, furrow width was 8% wider in the first irrigation and 24% wider in the sixth irrigation with clean tillage compared to conservation tillage.
Because large amounts of crop residue remain in the field following harvest, specialized and specially-adjusted equipment are often necessary when growing crops using conservation tillage technology under furrow-irrigated conditions. Equipment must be capable of operating in high surface residue conditions when performing field operations. Equipment developed and used in some cropping systems may not be suitable for use in conservation tillage under furrow irrigation--for example, most commercial grain drills will not operate properly when used for conservation tillage under furrow irrigation.
Despite the economic and environmental benefits of conservation tillage, it does have some limitations. For example, some crops used in desired rotations may require different row spacings; changing these row spacings from year to year may require field operations that make conservation tillage impossible. Simply harvesting some crops, such as potatoes, onions, sugarbeets, and dry beans, can cause considerable tillage. Including some crops in rotation can complicate or interrupt the use of conservation tillage. Additionally, periodic releveling fields that have been under conservation tillage for a period of time may be necessary to maintain uniform furrow-irrigated conditions; this leveling is difficult if large quantities of surface crop residue are present. Finally, nitrogen immobilization may be a problem during the establishment phase of conservation tillage; this is generally a short-term issue that can be readily overcome by applying additional nitrogen fertilizer. Concerns over potential increased nitrogen leaching when using conservation tillage with furrow irrigation have not been borne out by two separate studies in Western Colorado.