Home & Garden: Conservation tillage, a new way to reduce H2O runoff
Free Press Gardening Columnist
Conservation tillage is a concept which is hard to implement in the Grand Valley. While this soil and water conserving technology is not new, it is a new concept for many local farmers and thus somewhat scary.
Unlike burning off crop residue as we continually hear and read about (and smell due to the air pollution it creates), conservation tillage is a technique where a minimum of at least 30 percent of the previous year’s crop residue, such as corn stalks or wheat stubble, is left on the field. Like any other sustainable management technique, it takes two to three years before growers will see the full benefits of changing to this system.
Conservation tillage reduces soil erosion and runoff, and it increases microbial activity in the soil, which results in better tilth, increased crop production, better water infiltration, and increased nutrient holding capacity of the soil. One of the conservation tillage concepts, known as no-till, can leave up to 70 percent of the crop residue on the soil surface.
Farmers in this area resist the concept of conservation tillage due to a lack of understanding of how to use conservation tillage techniques in combination with furrow irrigation. If not implemented properly, plant debris can block irrigation furrows and impede movement of water from one end of the field to the other.
A demonstration of what happens when soil under a conventional tillage (i.e. plowing and disking) and conservation tillage is irrigated should convince the most ardent antagonist of the benefits of conservation tillage. The comparison of water-infiltration rate, water-holding capacity, and response of soil aggregates under both systems is unbelievable. With conventional tillage soil aggregates of sand, silt, and clay breakdown into their individual particles, resulting in the sealing of the soil surface restricting water and oxygen movement into the soil. Surface sealing is not as likely to occur with conservation tillage due to the high population of microbes holding these aggregates together. Soil aggregates are what make a soil healthy due to the macro pores between the aggregates that allow oxygen into the soil and carbon dioxide to leave. Oxygen is critical to root health and when prevented from entering the soil, root death occurs and root diseases increase.
Another water conservation method farmers can use is called the blocked-end furrow irrigation technique. Other than a field currently under sprinkler irrigation, blocked-end furrow irrigation is the technique I will be utilizing to irrigate lavender fields on Unaweep Avenue. This technique is designed for relatively level fields. Water is applied at a certain flow rate and allowed to run for a specific amount of time to ensure an even depth of water penetration for the length of the water furrow.
The amount of water that needs to be applied should be based on soil texture, the rooting depth and growth stage of the crop. Many growers let water run down the furrow for X number of hours without taken into account the above factors. The tail water resulting from this type of irrigation carries soil and nutrients out of the field and into the drainage ditch. The blocked-end furrow irrigation technique prevents these losses from occurring. In some states water restrictions prohibit tail water. And, when tail water does occur it must be pumped back to the head of the field and used for a later irrigation. Under these restrictions water applied to the field never leaves the field. Whether western Colorado farmers fall under such restrictive requirements will depend a great deal on the efficiency of their irrigation methods. Adopting conservation tillage practices will help reduce the implementation of such restrictions.
At a recent Farm Bureau meeting, John Stulp, director of compact negotiations for the Colorado River Interbasin Compact Committee (IBCC) discussed water conservation and how water supply planning is critical to ensuring a secure future for Colorado. Growers need to be part of this planning by increasing their efficiency in irrigation water use. Irrigation needs to refill the root zone of their crops while avoiding the deep percolation responsible for flushing salts and nutrients into the river. The only time excessive irrigation is truly necessary is when a leaching fraction is added to counteract problems of salty water. Unless growers are pumping out of a well, a leaching fraction should not be necessary as the irrigation water we obtained from the Colorado and Gunnison rivers is quite low in soluble salts.
Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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