Template:Chapters 6.8

6.8 - Crop rotation to suppress weeds in vegetable gardens

Thomas Jeneway, University of Guelph, Canada

Suggested citation for this chapter.

Jeneway,T. (2022) Crop rotation to suppress weeds in vegetable gardens. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

An Introduction to Crop Rotation

Weeds are a major problem for smallholder farmers, requiring women to spend up to 50% of their on-farm time removing weeds manually, which also reduces child literacy because children are pulled out of school during peak weeding times (FAO, 2014). Crop rotation is a system of changing which crops are planted sequentially over time to help balance and support the nutrients in the soil (FAO, 2003). However, research has shown that introducing crop rotation can not only increase net returns by up to 4 times but also reduce the cost of weed prevention by 50% with reduced time spent weeding (Lichtfouse, 2009). This reduction in such weed prevention can allow women more free time to invest in themselves and their families (FAO, 2003).

What Is Crop Rotation

Crop rotation is a simple method of changing what crops are planted in a field to help balance and support the nutrients in the soil (FAO, 2003). Rotating different crops between the same pieces of land allows for different nutrients to be absorbed and others to re-accumulate through the soil. Each crop will have its distinct usage of different minerals and nutrients. It is important to balance which crops are planted to return soil to its natural healthy state (FAO, 2003). The most important nutrient to keep balanced is nitrogen which can be done by planning and use of crops like legumes that are already grown in Africa (Mohler, 2022).

Benefits Of Crop Rotation In Terms Of Weed Control

A major benefit of crop rotation is reduced weeding and parasitic plants. Crop rotation allows for different species of crops to be interchanged between the same set of land, meaning that no one crop stays in a particular area for a long period of time (FAO, 2003). This means that the seed bank of parasitic plants that are able to germinate in the soil is reduced as the plants struggle to find a consistent host to rely on for their parasitic relationship (Rubiales & Aparicio, 2011). Weeds thrive on similar crops that have similar nutrient requirements so when farmers move away from the same crop(s) being planted every season, it prevents weeds from building up and adapting to the singular crop or intercrop that is growing (Ministry of Agriculture, 2012). Further diversifying the crop rotation (additional seasons with different crops) has been shown to decrease the weed density by up to 49% (Weisberger et al., 2019). To help diversify crops, cover crops can be included, which also decreases input costs such as nitrogen if a legume/green manure is included (Martens et al., n.d.). For example, in temperate countries, winter wheat rotated with maize was shown to cause a 12% reduction in the total weed seed bank. This was over a testing period of 6 years, leading to the conclusion that crop rotation is not a short-term solution like herbicides but provides long term benefits (Koocheki et al., 2008). Not only was the overall level of weeds reduced by crop rotation, but the composition of weeds was drastically changed, with over a 30% reduction of some of the most common weeds making up the total seed bank (Koocheki et al., 2008). Another study found when crop rotation and fertilizers were used in combination, crop rotation cut out any increase in weeds associated with improved soil fertility associated with adding fertilizers. Not only that, but tests found that crop rotation was able to reduce the weeds past the level normally found without fertilizer treatment (Chamanadad et al., 2006). Finally, the use of multiple crops allows for those who use herbicides to use different types, making it harder for weeds to build resistance to a particular one (Canola Encyclopedia, 2022). Overall, crop rotation leads to fewer weeds which means that women will have more time for other tasks or even the possibility of time for education. Crop rotation has the added benefit of reducing pests, further releasing women from tasks related to pest management (FAO, 2003).

Other Benefits

There are many benefits to crop rotation. Rotating different crops within the same piece of land allows for different nutrients to be absorbed and others to re-accumulate through the soil. Each crop will have its distinct usage of different minerals and nutrients (FAO, 2003). The most important nutrient to keep balanced is nitrogen which can be done by planning and use of crops like legumes within the rotation (Mohler, 2022). Using a crop like legumes alongside or between the desired crop can improve nitrogen levels by 50 to 200 pounds per acre (Mohler, 2022). This will save the farmer money and will ultimately be more sustainable (Flynn, 2015). Secondly, water consumption has been shown to be reduced by a successful crop rotation strategy. In one study, it was found that after a long-term crop rotation sequence, part of the system required 20-35% less water than without rotation (Lichtfouse, 2009). This means that even areas of low precipitation or water access can grow a wider variety of crops if they implement a crop rotation cycle (Lichtfouse, 2009).

Steps For Successful Basic Basic Crop Rotation

1. Identify the goals of your crop rotation

Examples:

Increase yield

Decrease weeds

Decrease cost

Increase soil health

2. Create a list of possible crops by group, with each group being a distinct cycle of rotation

Examples:

Legumes (beans)

Root Vegetables (sweet potato)

Leafy greens (cabbage)

Fruit-bearing (sweet corn)

3. Determine soil conditions and what crops suit them best

Simple tests:

3.1 Smell test for organic matter

3.2 Clump test for soil texture

3.3 Litmus paper for soil pH

3.4 Soil colour for aluminum determination

4. Split the garden space into different plots

5. Decided what crop you would like to plant in each plot, with each plot to contain only a single crop species,

6. After a single farming season, rotate the crops in a constant pattern

7. After multiple seasons, readjust the crops and plan according based on knowledge gained

Critical Analysis

Even with crop rotation, diseases can still build resistance to the changing circumstances that the system offers (Canola Encyclopedia, 2022). This can happen because farmers use too few crops in a rotation, allowing diseases and even pests to survive in the soil long enough for the next appropriate host crop to be planted. This process can, over time, allow for weeds and pests to adapt and evolve to these conditions (Canola Encyclopedia, 2022). In addition, some diseases are unaffected by crop rotation and as such need to be combined with other techniques to reduce weeds (Chamanadad et al., 2006). Furthermore, a study found that successful reduction in weeds from crop rotation relied on other factors like tillage (Colleen et al., 1999). Another reason that some farmers do not implement crop rotation is that it reduces flexibility, since they must follow a specific planting cycle over long periods of time (Selim, 2019), perhaps reducing their ability to exploit and/or respond to changes in commodity prices (Chamanadad et al., 2006). Furthermore, starting crop rotations can cost more than monoculture, as farmers are forced to buy a diverse range of seeds in smaller quantities (Selim, 2019). Crop rotation is truly a long-term investment made to improve soil quality and crop yield while ultimately reducing weeds including parasitic plants.</p.

Figure 1. Explanation of a crop rotation http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.__sak_north_africa_middle_east_dec_2016_compressed.pdf.

Links to Useful Resources

https://extension.psu.edu/start-farming-planning-a-crop-rotation - Helpful tips for planning a crop rotation and useful chart for knowing different types of crops.

https://www.organic-africa.net/fileadmin/organic-africa/documents/training-manual/chapter-02/Guidance_note_Poster-5_Crop-rotation-vegetables.pdf - Helpful poster for organic crop rotation

https://www.accessagriculture.org/crop-rotation-legumes - Video of Crop rotation with legumes

https://youtu.be/YhyPlrQN64A - Basics of Crop Rotation

https://youtu.be/XeNA6XdMoF8 - Summary Video of Crop rotation on a small scale

References

1. Canola Encyclopedia. (2022, May 6). Crop rotation. The Canola Council of Canada. Retrieved November 8, 2022, from https://www.canolacouncil.org/canola-encyclopedia/field-characteristics/crop-rotation/

2. FAO. (2003). Gender and Development. Gender and Development Plan of Action. Food and Agricultural Organization of the United Nations, Rome. Retrieved November 8, 2022, from https://www.fao.org/3/Y3969E/y3969e04.htm

3. FAO. (2014). Youth and Agriculture: Key Challenges and Concrete Solutions. Rome, Italy: The Food and Agriculture Organization of the United Nations.

4. Flynn, R. (2015, June). Nitrogen Fixation by Legumes. BE BOLD. Shape the Future. New Mexico State University Retrieved November 8, 2022, from https://pubs.nmsu.edu/_a/A129/

5. Koocheki, A., Nassiri, M., Alimoradi, L., Ghorbani, R. (2008, October 31). Effect of cropping systems and crop rotations on weeds. Agronomy for Sustainable Development, 29, 401-408. https://doi.org/10.1051/agro/2008061

6. Lichtfouse, E. (2009). Organic Farming, Pest Control and Remediation of Soil Pollutants: Organic farming, pest control and remediation of soil pollutants. Netherlands: Springer Dordrecht

7. Martens, J. T., Derksen, D., Entz, M., Irvine, B., et al. (n.d.). Cover crops. Weed Management Options: Cover Crops. Give source. Retrieved November 8, 2022, from https://www.umanitoba.ca/outreach/naturalagriculture/weed/files/singleseason/cover_crops_e.htm

8. Chamanadad, M., H. R., Tulikov, A. M., Baghestani, M. A, et al. (2006, December). Effects of Long-Term Fertilizer Application and Crop Rotation on the Infestation of Fields by Weeds. Turkey Journal of Agriculture and Forestry, 33, 315-322. https://doi.org/10.3906/tar-0712-47

9. Mohler, C. L. (2022, September 1). Crop rotation effects on soil fertility and Plant Nutrition. Sustainable Agriculture Research and Education. University of Maryland. Retrieved November 8, 2022, from https://www.sare.org/publications/crop-rotation-on-organic-farms/physical-and-biological-processes-in-crop-production/crop-rotation-effects-on-soil-fertility-and-plant-nutrition/

10. Rubiales, D., Aparicio, M. F., et al. (2011, August 4). Innovations in parasitic weeds management in legume crops. A review. Agronomy for Sustainable Development, 32, 433-449. https://doi.org/10.1007/s13593-011-0045-x

11. Selim, M. M. (2019). A review of Advantages, Disadvantages and Challenges of Crop Rotations. Egyptian Journal of Agronomy. 41, 1-10. http://dx.doi.org/10.21608/agro.2019.6606.1139

12. Weisberger, D., Nichols, V. Liebman, M., et al. (2019, July 18). Does diversifying crop rotations suppress weeds? A meta-analysis. PLOS ONE. 1, 1-12. https://doi.org/10.1371/journal.pone.0219847

13. Doucet, C., Weaver, S.E., Hamill, A.S. and & Zhang, J. (1999). Separating the Effects of Crop Rotation from Weed Management on Weed Density and Diversity. Weed Science, 47, 729–735. doi:10.1017/S0043174500091402