Does fallow have a role in direct seeding in the southwest? Well, there are several reasons why farmers summerfallow. Essentially the main reasons why farmers include fallow in their rotation are for weed and disease control and soil moisture conservation. Direct seeding has often been looked on with skepticism in the south west for these very reasons. However, there are many farmers who have adopted direct seeding in the south west that have successfully and dramatically reduced the amount of fallow in their rotation or have eliminated fallow altogether. In addition, in the majority of these cases, the method of fallow has also changed from tillage to chem-fallow.
Weed and disease control has long been one of the primary reasons for maintaining tillage-based fallow. Your success is readily evident and the practice has been around a very long time so farmers tend to be very comfortable with it. Many farmers believe that tillage also helps reduce disease problems. However, research has shown that there is actually less disease problems under direct seeding as compared to conventionally tilled systems. For weed control, there often is a mistrust of relying solely on herbicides by many farmers which also helps justify conventional tillage practices. However, poor weed control using tillage under wet or very moist soil conditions is not uncommon and is very often not given the same criticism. In addition, under low disturbance direct seeding, some factors are generally not acknowledged by those considering changing to this system. First of all, by switching to a low disturbance system (seedbed utilization of 50% or less), many weed problems are significantly reduced. Many weeds rely on mechanical disturbance in order to germinate. Wild millet (green foxtail) and kochia are two good examples of this. Wild oats is another major problem weed that tillage promotes its growth. Low disturbance direct seeding minimizes this problem and combined with shallow seeding, helps to reduce the depth of the "seed bank" in the soil. The narrowing of the depth of the seed bank will also allow the zero-incorporated granular herbicides to be most effective.
Crop rotation is often an overlooked aspect of weed control. For direct seeding to be truly effective and profitable, the cropping rotation needs to be expanded from only cereals. Research indicates that a continuous cereal rotation is the least economic rotation. Once one or two broadleaf crops are included in the rotation, the advantages to weed control and improved soil quality can be realized. Most crops can out compete weeds as long as they emerge before the weeds and form a canopy. Low disturbance direct seeding will improve crop emergence before the weeds. Rotating broadleaf and cereal crops also forces you to change herbicides and the herbicide grouping. This can help control grassy weeds in broadleaf crops and broadleaf weeds in cereals. Changing herbicide groups will also break any herbicide resistance problems that may be developing.
Expanding the crop rotation will also improve the soil by increasing the organic matter and in the case of pulses, add nitrogen to the soil. Every tillage operation breaks down existing soil organic matter. The 50/50 conventional system over the last 70 to 80 years, combined with excessive tillage operations, has been responsible for a significant loss of soil organic matter in our soils. Organic matter in the soil helps retain soil moisture and will be a major factor in how readily many soils will crust. It is also a major nutrient store. Direct seeding helps to maintain and increase the amount of organic matter in the soils. Many farmers have expressed significant changes in their soils the longer they direct seed. "The soil has become much more mellow and doesn't crust as easily" is a common comment I have heard.
Soil moisture is probably the most limiting factor to us in the south west. Conserving this soil moisture is probably one of the major challenges for farmers. Summerfallow has been one of the traditional methods used to conserve moisture. However, it is actually a relatively inefficient system of storing moisture. Usually only about 10-15% of the annual precipitation is stored. If one can store as much or more through snow trapping in standing stubble, why would you opt for summerfallow? Other snow trapping practices can be employed to increase the amount of moisture that can be stored in the stubble. If the organic matter in the soil has increased and there is good surface residue left due to low disturbance direct seeding, the potential for extending your cropping rotation from the traditional two-year, 50/50, to three or four years is definitely there. Maintaining good surface residue will also help keep the moisture that is stored in the soil through reduce evaporation and wind speed. Problems with heat cancor and shearing of the seedlings are virtually nil under direct seeding as compared to crops seeded on summerfallow.
Chem fallow is a good option to consider if fallow is used in your extended rotation. With the relatively low cost of non-selective herbicides like Roundup, it is hard for three or four tillage operations to compete economically. In addition, just look at the amount of erosion from wind and water that occurs on any summerfallow field compared to that of a chem-fallowed field or fields direct seeded. Erosion is a short-term and long-term cost!
Now after promoting the benefits of chem-fallow, there are instances where tillage has a role under direct seeding. Some weeds like established stands of foxtail barley are very difficult to control economically with herbicides. In the case of foxtail barley, discreet tillage or spot tillage of patches can be very effective. If there is widespread infestation of this weed across the whole field, it may be more effective to use tillage for that year and get control of it. However, as mentioned before, crop rotations can also be utilized and be very effective in controlling this pesky weed.
The whole concept of direct seeding is still relatively new to farmers in the south west. As in most cases with something new, farmers will watch their neighbour and see how it will work before making the switch themselves. Another constraint to those making the switch is there tends to be a time lag of a few years before some of the benefits of low disturbance direct seeding become evident. However, those that stick with it have all observed and realized the benefits of direct seeding. Although it is unlikely that we will see the elimination of summerfallow in the south west any time soon, we are seeing a reduction of summerfallow acres, more chem-fallow when there is fallow, and more farmers are extending their rotations. These are all positive steps and will help to increase the soil quality and resistance to factors such as drought and erosion. By remaining flexible in the farming operation, direct seeding can help to improve the bottom line and the soil.