Crop rotation basics

From Tiny Farm Wiki

Crop rotation is means not growing the same crop in the same place two years running. Moving crops around is practiced to avoid the buildup in the soil of pests and diseases specific to a specific crop. Also, crops have different nutrient requirements, and rotation helps to avoid creating a nutrient imbalance in the soil.

I've used a modified version of Coleman's 8-year rotation (from New Organic Grower) for five seasons, and I can't honestly say I've noticed benefits. What I mean is, it makes sense to rotate crops, but it's hard (at least, for me in my size garden) to actually say, "Oh, this did better, or that wasn't overrun by pests, because of the rotation." I'd have to do little experiments, like growing a few tomatoes in the same spot for a few years, trying two rotations side by side, and so forth, to actually compare results. Meanwhile, I rotate on faith, and everything seems to be doing well!

By the rules of thumb, you want to separate tomatoes and potatoes and others in that family as far as possible, so in an 8-year, you could have them four years apart.

Also, IF peas/beans contribute significant nitrogen that carries over to the next season, then you may want to have them before the brassicas, which are definitely heavy feeders. (I say "if" because in theory they're supposed to, but how they're planted, when they're harvested, how the residue is incorporated and so forth, I'm sure determines the nitrogen contribution, it's not an automatic thing, like, "plant peas, get useful nitrogen carryover." I'm still trying to find answers for this.)

[edit] Crop rotation based on fertility requirements

I was introduced to crop rotation based on fertilization requirements by Yves Gagnon during one of his organic gardening workshop. I have never personally tried it as I have only a tiny garden, but it does make to me hence why I want to share.

For this rotation, annual vegetables are grouped in four categories:

• Heavy feeders of young compost. These are the crops that require a lot of nitrogen such as solanacae (tomatoes, eggplants, peppers and cie), cucurbit, artichoke, sunflower and corn. Potatoes and ground cherries, while member of the solanacae family, are not part of this group.
• Medium feeder of well-finished compost. Crops that require lots of fertilisation, but not too much nitrogen. Include most of the brassica, lettuce, celery, spinach, potatoes, onion and garlic, and others.
• Light feeder. Those that requires little to no fertilization, and includes almost all root crop and legumes (bean and peas).

The rotation is based on four years. The garden is divided into four plots, each divided into two (or more) subplots. Let's call call them 1a, 1b, 2a, etc until 4b.

Rotation start with green manures, being cultivated on one plot for one year. As such, green manures always occupy at least 25% of the garden (or more, if you count intercropping, green manure cover crop in other plots, etc). The other three plots grows each one of the three groups discussed above, each in succession. The succession would look like:

   Green manure -> Heavy feeders -> Medium feeders -> Light feeders

You would not fertilize green manure. You would apply young compost to heavy feeders, and well-finished compost to medium feeders. You would apply no, or very little, compost to light feeders. Heavy feeders would benefit from the preceding green manure and young, nitrogen-rich compost. Medium feeder will profit from some of the heavy feeders residual fertility, plus well-finished compost applied in adequate proportion. Light feeders would live on the residual fertility of both the heavy and medium feeders.

Plots being divided into subplots, you will grow only one of the main family in each subplot; for example, in the heavy feeder plot, cucurbit would grow in subplot a, and solanacae in subplot b. When the rotation begin a second cycle, you would invert them (solanacae in subplot a, and cucurbit in subplot b). You would do that for every group. This will ensure the same crop will not grow on the same plot for eight years.

Example rotation (this may need tweaking for other factors beside fertilization):

There are pros and cons to this type of rotation.

Pros:

• Easy to understand and to remember
• Make sense, as vegetables within a family usually have similar fertilization requirements

Cons:

• Assume standard-sized subplot. What if you want more squashes than a single subplot worth of it?
• Some discrepancies in fertilization needs within family, most notably potatoes and other solanacae.
• Classification of vegetable in groups is tricky. For example, some says pepper are medium or light feeders, not heavy.
• Those with perennial culture (strawberries, for example) will have to adapt the plan for multi-years crop.

[edit] External links

• Vegetable Crop Rotation - A good, quick summary and how-to, perfect especially for the smaller garden wanting to get started with a minimum of fuss!