Summerfallow Tillage – Austen Preete

Summerfallow tillage is a useful technique when wanting to reduce the seedbank within a field. Since there is not a crop being grown that season, the grower has the ability to allow the entire weed population to germinate before a tillage practice is applied. The goal is to allow as many weed species as possible to germinate, and allow those species to reach peak germination, then turn the weeds under with tillage before seed is set. This technique is especially useful on weeds with short dormancy periods such as kochia, wild buckwheat, green foxtail, and foxtail barely.  This form of tillage will assist in attacking perennial weed problems, while reducing the seedbank of annual weeds (Frick et all. 2012).

Applying three to six tillage operations may be required for effective annual weed control during the fallow year. This can be achieved by starting early in the spring with the first tillage operation, which must be the deepest pass to bring up the seeds to the soil surface. After the first pass, the subsequent tillage operations should become progressively shallower. For improved production, till while the soil surface is warm and dry because tilling in moist conditions may result in small seedlings being transplanted rather than killed (Frick et all. 2012).

Summerfallow tillage is an effective practice used in controlling weeds, but it causes the field to become exceptionally susceptible to soil erosion. To counteract erosion, a grower must implement tillage with caution. Repeated cultivation will lead to a depletion of organic matter in the soil. Leaving additional straw or chaff on the field from the previous year provides the soil with protection from environmental conditions, such as wind and water. Also, a grower can utilize shelterbelt growth for fields that experience perennial weed issues because it will combat against erosion for when summerfallow practice is applied (Encyclopedia. 2006).

Figure 1: With only a limited amount of cover, the soil is able to absorb approximately 60% more moisture compared to the field without any cover. This will lead to an increase in soil erosion while a field is bare. Linked image from http://www.apsim.info/Portals/0/APSoil/SoilMatters/images/mod1/fig1-03.gif

Personally, I feel the value of this technique is somewhat dated and becoming increasingly unpopular. The reason for this decline in popularity is due to the detrimental effect it has on both economic and ecological costs.  Using the summerfallow tillage method entails that a farmer cannot grow a crop on a field that he/she is paying for. The opportunity cost that the grower faces not sowing a crop that year will most likely outweigh the price he/she pays for yield loss caused by the weed populations. In addition, the erosion caused by repeatedly exposing moist soil to the environmental conditions will quickly deplete the soil structure. Poor soil with a lack of fertility will cause more yield loss than nutrients being depleted by interspecific competition with weeds. The summerfallow tillage practice works effectively, but the cons outweigh the pros in most instances. Therefore, it should be practiced in desperate situations when a field is becoming overwhelmed by an aggressive seedbank that is annually increasing in population size.

Figure 2: A graph demonstrating the decline in popularity regarding the use of summerfallow in Saskatchewan since 1990. Image linked from http://www.parc.ca/saskadapt/assets/images/soil-conservation-fig3_lg.jpg

References

Frick, B. Johnson, E. Organic Agriculture Centre of Canada. 2012. Summerfallow as a weed   management strategy- pros and cons. http://www.organicagcentre.ca/extension/ext_weed_summerfallow.asp

The Encyclopedia of Saskatchewan. 2006. Summerfallow. http://esask.uregina.ca/entry/summerfallow.html