Every drop counts! Water management in potato

Conserving water is important for adapting to climate change, and is crucial for smallholders growing potatoes in semi-arid regions. Collaboration between CIP and institutions in Kenya and China highlights appropriate techniques for saving water: intercropping with legumes and partial root-zone drying irrigation.

Across the world, potato growing helps smallholders to generate income and feed their families. Yet many smallholders cannot afford the irrigation, fertilizer and plastic mulch which are often suggested for growing potatoes. Recent research offers hope for profitable, environmentally friendly technologies to save water without sacrificing tuber yield.

Intercropping can help potatoes to retain soil moisture, but until now there has been little research on legume-potato intercroping. A recent collaboration between researchers from CIP and the University of Nairobi compared monocropped potatoes with legume intercropping. Harun Gitari, Elmar Schulte-Geldermann and colleagues looked at an intercrop of potatoes with dolichos (lablab), garden peas and common beans. The fields intercropped with legumes had more ground cover and the soil retained more moisture than potato monocrops. Potatoes intercropped with dolichos kept more soil moisture than any other treatment. Potatoes grown with dolichos only suffered a slight yield loss. In a semi-humid area of Kenya, the same researchers also found that potatoes intercropped with legumes grew roots that were up to 35% deeper, allowing the plants to absorb moisture from deep within the soil, even when the top 30 cm were too dry for the potato roots to capture water. The intercropped legumes provided more shade that kept the soil moister and cooler– just right for potatoes. The legumes themselves can also be eaten, contributing to the families’
food security.

China is the largest potato producer in the world, growing over one quarter of the global total—yet much of the crop is planted in semi-arid regions where water is valuable. One disarmingly simple way to use water more efficiently is to irrigate only half of the field at a time.

A recent study by Junhong Qin and colleagues at CIP and the Chinese Academy of Sciences compared full furrow irrigation with two water-saving techniques in Zhangbei County, China. One of the water-conserving techniques was drip irrigation, where perforated PVC pipe or special soft-plastic drip hoses irrigate the base of each plant drop-by-drop. The second water-saving method, “partial root-zone drying furrow irrigation,” or PRD, only waters every other furrow. Half of the furrows are watered one time, and the other furrows are watered the next time the field is irrigated.

Potatoes grown alone (left) leave a lot of soil bare, but potatoes intercropped with lima beans (center) or dolichos (right) cover the ground and retain more soil moisture. D. Ramirez/CIP

When the young potato plants are deprived of water, they synthesize a hormone (abscisic acid) in their roots. The hormone closes the stomata in the plant’s leaves, reducing water loss. A thirsty plant learns to lose less water.

When the experiment was started at the moment tubers were beginning to form, drip irrigation and PRD used only half as much water as full furrow irrigation. But by starting irrigation two weeks later, water use could be decreased to 36% of the full furrow requirement.

The potato yield was the same with all three treatments: PRD, drip irrigation and full furrow irrigation. But PRD saves the costs of installing the drip irrigation system, reduces carbon emissions and avoids the plastic pollution caused by disposing of the drip irrigation tubes at the end of their life. PRD saves half the irrigation water of full irrigation, but without sacrificing potato yield.

Intercropping potatoes with legumes and PRD irrigation are two examples of appropriate technology that can offer practical ways of saving water in a thirsty world while maintaining productivity.