Rotating your crop
I’d like to make a bold statement that the majority of commercial farmers in Hawaii don’t practice crop rotation. By not rotating our crops, we create our own problems that can be the cause of own demise. Monoculture is the simplest form of farming because you only have to understand all aspects of one crop, so you can grow it well if you choose, but in the process, you create insurmountable problems for you, the farmer, and your crop.
The key word here is "create." The farmer creates his own problems, such as spotted wilt virus on tomato and lettuce, papaya ringspot virus on papaya, and root-knot nematodes on many crops to the point where we can no longer grow the crop in certain areas of the state. Then we need to come up with costly and time-consuming solutions which may not fit into our farming ethic, including geneticallymodified crops.
Man is his own worst enemy and doesn’t learn from the natural systems around him. We’re driven more by shortterm horizons such as markets and by land tenure, and not by focusing on soil health and management. In creating a crop rotation system, a more holistic approach needs to be embraced, and all of the pieces of the puzzle need to be taken into consideration equally. There are short, medium, and long-term considerations in planning a crop rotation strategy.
Markets are a short-term consideration, and can get very complicated if you’re growing an array of crops. Crop rotation can break pest cycles which can be very costly to control over the long run, and can foster the proper use and recycling of soil nutrients without depleting some of them. In Hawaii, we’ve seen the impacts of not implementing crop rotation. It’s more the norm not to implement a rotation system, and by doing this, we end up like a dog chasing his tail, wondering why we’re in a situation that we ourselves created.
A crop rotation system utilized for decades in Kula was the lettuce-tomato rotation, and this was a disaster resulting in millions of dollars in crop losses over the long-term. The problem was that both crops were susceptible to Spotted-Wilt virus, once referred to as the AIDS of the plant world because it killed its host. This rotation eventually led to the demise of both crop industries on Maui that hasn’t yet recovered. The other crop that’s experiencing a similar problem due to the lack of a crop rotation is head cabbage.
Head cabbage is grown most of the year in Kula, so the pests are always there constantly evolving and building resistance to pesticides to the point where a three-pesticide regime must be followed in order to prevent pesticide resistance. Farmers have also had to shift to a new cabbage variety that’s more tolerant to insect damage. A tougher, more insect-resistant variety, Scorpio, is being grown, but what they gave up was a very sweet cabbage variety, Tastie. Some farmers have resorted to flattened head varieties from Japan that’s more adapted to Hawaii’s conditions, including heat- and insect tolerance.
Farming in Hawaii is "a different animal" so we may have to retrofit strategies for a pono farming system, but some basic concepts still apply. Here’s a list of crop rotation concepts or strategies taken from three important books on the subject, and I know there’s more:
- The rotation must adapt itself to the farmer’s business.
- It must adapt itself to the soil and fertility problem.
- The fertilizer question also modifies the rotation.
- The kind of soil and climate may dictate the rotation.
- The labor supply has an important bearing on the character of the rotation course.
- The size of the farm and whether the land can be used for pasturage are also determinants.
- The rotation must be planned with reference to the species of plants that will best serve one another, or produce the best interrelationship possible.
- Deep rooted crops must follow shallow rooted crops.
- Alternate between crops with high and low biomass.
- Follow a legume crop with a high nitrogen demanding crop.
- Grow the same annual crop for only one year.
- Don’t follow a crop with a closely related species.
- Alternate between leaf and straw crops.
- Use crop sequences that aid in controlling weeds.
- Use longer periods of perennial crops on sloping land.
- Grow some crops that will leave a significant amount of residue.
Although some of these guidelines may not fit into your farming system, it’s a good idea to incorporate as many of these guidelines in your farming system as possible. We need to create more GAPs or Good Agricultural Practices as we refine crop rotation systems for Hawaii.
University of Hawaii College of Tropical Agriculture and Human Resources
Cooperative Extension Service, Molokai
Check out Glenn's The Molokai Native Hawaiian Beginning Farmer Newsletters archived at http://www.ctahr.hawaii.edu/sustainag/NewFarmer/newsletters.asp