Peter and I (Anna) been in China this past week, looking at potential drip irrigation customers; the farmers who are most interested are the proud owners of low-cost greenhouses. These simple greenhouses are covered with a clear polyethylene film, which lets light in but traps heat. The back and side walls of each greenhouses is a thick brick and earthen wall; during the day, this heats up, and at night, that heat is released slowly, keeping the greenhouse nice and toasty even in the coldest frozen days of winter. We’ve seen hundreds of these greenhouses in use now, and hundreds more under construction: they all follow a simple formula of Nine Four One One Five: The greenhouse is nine meters wide and four meters tall at the back wall; the heatsink walls are one meter thick; and the angle of the polyethylene front wall is 15 degrees. For the last dimension, length, there’s a bit more variability: some of the greenhouses we visited were about 50 meters long, while others stretched to just over 100 meters.
Inside, the farmers are growing beans, tomatoes, radishes, and all sorts of greens; they say that now that more Chinese are living in cities and getting higher salaries, demand for vegetables has gone way up. In the summer, it’s pretty easy to grow good vegetables outdoors, but with a first frost date in November and a last frost date in March, it’s hard to get fresh vegetables year-round without a greenhouse. These greenhouses are fairly easy to build, and the heatsink keeps inside temperatures above freezing year round, with no need for electric or propane heaters. They’re actually warm enough that the new models are constructed with a living space for a family attached at one end—the heat from the greenhouse cuts way down on families’ winter heating costs, and it’s quite convenient to be able to step from your kitchen into your greenhouse.
Redistribution of land in China means that everyone's got a fairly equal amount of land-- but that amount is small. Most families have 1-2 Chinese acres; since each acre is only 667 square meters, that's not much space for rain-fed crops. Greenhouses, however, can produce two crops a year, and the vegetable crops sell for much higher prices than grains or legumes. The greenhouses we visited covered anywhere from 25-100% of a family's total land, and the farmers said that the higher incomes from vegetable crops have made an amazing difference in their lives. The only problem is that year-round cultivation means year-round watering. The government wants to encourage farmers to make their land more productive by building greenhouses, and so they subsidize the cost of electricity for water pumping. However, both power and water are limited resources, and the government workers we met with were interested in any way these resources could be used more efficiently. They like the idea of drip irrigation because it will reduce water use, and thus electricity use, without reducing yields-- in fact, yields should increase as water distribution efficiency is improved.
Right now these farmers water by hand, from a hosepipe in the center of each greenhouse. It works well enough right now, but takes a lot of time. As more greenhouses are built, that time becomes more precious; the farmers we talked to want to be able to just turn on a drip system and let it run while they do other work in the greenhouse, weeding, pruning, and harvesting. Since many of them grow tomatoes, drip will be useful for applying water directly to the plants’ roots and avoiding splashing soil up onto the leaves; tomatoes are very vulnerable to soil-borne fungal diseases, and the moist, warm conditions of a greenhouse mean an infection can spread quickly. We’re hoping our drip will free up the farmers’ time so they can keep working on expanding their greenhouses, and keep the crops healthier.