Growing the same crop in the same place for many years in a row disproportionately depletes the soil of certain nutrients. As I mentioned in last weeks post (here), crop rotation gives various nutrients to the soil, especially replenishing nitrogen in the soil. The focus on maintaining soil health ensures the health of the environment than more intensive systems brought on by Big Agri business. Other reasons for rotating crops include: preventing soil erosion and compaction of the soil, preventing the progression of pathogens and pests which occurs when one species is continuously cropped.
Plants that uptake a lot of nutrients from the soil include Cabbage, Cauliflower, Brussels, and Broccoli. Because of this, gardeners should follow these heavy feeders with light feeders such as root vegetables, or follow with nitrogen fixing vegetables such as peas and beans.
Perennial plants need no crop rotation, of course, so I am specifically speaking on summer and winter annual plants.
Crop rotation works best as a three or four year garden plan because "this is the number of years it takes for most soil-borne pests and diseases to decline to harmless levels" (growveg).
Beans, which uptake nitrogen from the air, add nitrogen to the soil. This is why many farmers grow beans one year, then corn is grown the following year in the same place, because corn uptakes a lot of nitrogen from the soil. "Every year the plants grown in each given area are changed, so that each group (with its own requirements, habits, pests and diseases) can have the advantage of new ground. If your beds are divided into four groups, this means that members of each plant family won’t occupy the same spot more than once in a four-year period" (growveg).
Dividing crops into four main groups (legumes, roots, leafs, fruits) becomes too simplified when practicing crop rotation. The growth habit of these groups does not bear on the classification of the plant. For example, potato and tomato are in the same family, so they may attract the same pests and uptake the same nutrients from the soil. To begin incorporating crop rotation, first identify the crops you want to grow, and then keep plants of the same type together in one area. Remember that Brassicas follow legumes. For example, sow cabbage, broccoli, cauliflower on soil previously used for beans and peas. GrowVeg provides a crop rotation table that may assist you when growing in four different areas:
||Enrich area with compost and plant potatoes and tomatoes (Solanaceae). When crop has finished sow onions or leeks (Allium) for an overwinter crop.
||Sow parsnips, carrot, parsley (Umbeliferae). Fill gaps with lettuce and follow with a soil-enriching green manure during winter.
||Grow cabbage, kale, arugula (Brassicas) during the summer and follow with winter varieties of cabbage and Brussels sprouts.
||If this is your second or subsequent year, harvest the onions or leeks previously growing here over winter. Then sow peas and beans (legumes). When harvest has finished, lime the soil for brassicas which will move from area three to occupy the space next.
|Incorporating polyculture and companion planting, such as the three sister's method, offers more diversity and complexity within the same season or rotation. The three sister's is a polyculture system where corn, beans, squash are grown together. While the corn grows tall, the beans vine up the stalks and replenish nitrogen to the soil, while squash trails on the ground to prevent weeds growing amongst the vegetables. For more details on polyculture systems like three sisters method, go to my post on Permaculture here, No money, work, or tilling involved: Permaculture.
Companion planting and crop rotation offer many benefits, especially when growing on Hugelkultur mounds. This is another permaculture technique which I discuss in detail in the link I posted above. Hugelkultur is a layering system of decaying wood which adds nutrients and water within the soil through the fungal activity in decaying wood. From my experience after growing food on Hugelkultur mounds for the first time this year, I am amazed at the growth and productivity. I highly recommend adopting Hugelkultur in place of tilling practices.
Overall, the practice of crop rotation in sequence with companion planting and growing in Hugelkultur mounds will retain water deep in the soil, reduce watering while preventing erosion (maintains soil structure), avoids nutrient depletion in the soil, pests or soil-born disease, eliminating the use of fertilizers, and controls weeds.
On a final note, keep records of your garden and successes and failures. Play the scientist role, and do experiments, make observations, conclusions. Remember when beginning crop rotation, that members of any given family should not be grown in the same sport for more than one year. Secondly, vegetables from different groups can share a plot if they require the same conditions.
The overall message here today is that these permaculture practices reduce environmental pollution, reduce greenhouse gases from food production, reduce or eliminate any unethical treatment of insects, animals, and the environment.
Original post @ Crop rotation: Fruits to Roots to Legumes to Leafs