Water Use Efficiency


Once water has been captured and retained in soil, it is important to ensure efficient use by plants. Available water for a particular crop equals the sum of the stored available soil water and the rainfall that is received during the crop growth cycle.

The amount of soil water available to a crop is controlled by its rooting depth. Crops such as winter wheat and sunflower extract water from depths of six feet or more if there is no dry soil layer in the profile. Corn roots extract water to at least five feet, while perennial crops like alfalfa may extract water up to a ten foot soil depth. In areas that have excellent water holding capacity, the six foot soil reservoir, if at field capacity, is substantial for most crops. Soils within the loam to silty clay loam textural classes will contain 12 to 15 inches of plant available water in a six foot depth if at field capacity. No-till provides the best opportunity to reach the field capacity water content.

During hot summers, a full water profile protects the crop during dry periods. However, the soil water profile generally will not be large enough to carry most crops through to maturity with no rainfall. At a plant water use rate of 0.2 to 0.3 inches per day, a profile of 14 inches of water would supply the crop for 45 to 60 days. Thus, the capture of the precipitation that occurs during the crop cycle also is critical.

The most critical growth stage for water availability in plants is always during the reproductive period. The combination of stored water and rainfall is needed to meet the water needs during this period and thus maximize grain yields. No-till practices will maximize soil water storage and provide the best chance of maintaining the crop, even when summer rainfall is lacking or is untimely. It is best to choose crops for rotation that have their critical water need when rainfall is most expected. Wheat and other cool season plants are well suited to these conditions. The reproductive stages of corn and sunflower occur later in the summer and are more likely to experience stress than wheat. In all cases, maximizing soil water storage before planting is extremely important, and no-till practices are most useful in achieving this goal.

Adequate fertilization, especially with nitrogen (N) and phosphorus (P), is critical to getting the most out of precipitation and stored soil water. Research at Akron, Colorado showed that wheat roots require adequate fertilization to exploit the entire soil profile. Soil tests and appropriate crop yield goals help determine the amounts of N and P required. Intensified cropping systems, where more crops are being harvested, will have greater fertilizer requirements, especially N, than WF systems. Adequate fertilization allows you to realize the maximum profit from the water you worked so hard to save.

Barriers to Diversifying Cropping Systems

1. Learning about and applying new technology. The learning curve can be steep for operators unfamiliar with chemical weed control, but working with neighbors who have successfully adopted diversified cropping systems is an excellent means of making a smooth transition. Local agricultural chemical dealers also are excellent sources of information.

2. Purchasing the equipment required for effective no-till management. You will need a good sprayer that meets your crop-specific demands. Custom herbicide application is available, but owning your sprayer insures timeliness of important operations. It should be equipped with a good marker system or have an electronic guidance system. You will also need planting equipment designed to handle surface residues. Depending on the crops you choose to produce, you may need to purchase both a grain drill and a row planter. However, if you choose a WMF rotation, a grain drill will suffice for all planting operations.

3. Learning how to be timely with all operations, especially herbicide applications for weed control. The old stubble mulch WF system is very forgiving in terms of timeliness of tillage weed control. Effective herbicidal weed control requires timely applications to get the best performance from the chemicals. Managing weeds in no-till systems requires a watchful eye at all times.

4. Being familiar with lease agreements. The old crop share ( 2/3 tenant and 1/3 landlord) contract, where the landlord invests only in 1/3 of the fertilizer expense, is not adequate for a diversified intensive cropping system. Either the crop share must be adjusted, or the landlord must pay an appropriate share of herbicide and seed expenses.

Fortunately, many producers have successfully overcome all of these barriers and are now profiting from their conversion from stubble mulch WF to a no-till diversified cropping system.