Improving soil health in potato cropping systems

A recent Soil Science Society of America’s (SSSA) Soils Matter blog explores options to improve soil health for crops that grow underground – like potatoes.

Potatoes are a valuable crop in Washington state. It is the second leading producer of potatoes in the United States (after neighboring Idaho). The potato industry in Washington recognises the importance of healthy soils for long-term, sustainable production of the crop.

Planting and harvesting potatoes disturbs the soil

One issue with growing potatoes: they are a tuber crop, growing belowground. Thus, planting and harvesting them disturbs the soil more than a crop like wheat or barley, which are harvested aboveground. Growers and researchers are working on strategies to promote soil health in this typically high disturbance system.

Through Washington’s new Soil Health Initiative, soil scientist Deirdre Griffin-LaHue and her team recently set up a long-term rotational experiment to explore some of these strategies in potato-based systems. The strategies represent the typical rotations and soils of the area. The trial is designed with methods that use changing levels of:

• soil disturbance (i.e., tillage),

• organic matter inputs,

• internal (cover crops and residues) and,

• external (compost).

This allows the team to study multiple soil health principles and how they interact with one another.

Potatoes in northwestern Washington are typically grown in a particular field every 3-5 years. Soil improvement strategies are really focused on what happens before and after the potato crop.

Cover crops

One practice many growers are experimenting with is using cover crops. Cover crops are grown between cash crops to provide agroecosystem benefits related to 3 of the 4 main soil health principles: cover the soil, increase diversity, and maximize continuous living roots, which help feed microorganisms in the soil.

Farmers in the area are using two methods. One is winter cover crops, planted in fall and terminated in spring. The other is multi-year cover crops that are mowed and continuously provide organic carbon inputs to the soil.

Washington’s cold, wet fall and spring seasons can be a challenge to establishing winter cover crops. This is due to harvesting potatoes through October. But having cover crops between all other rotational crops may still benefit the soil.

Minimising soil disturbance

The team is also studying potato-growing systems that reduce soil disturbance. They are looking at whether it’s both feasible and beneficial to rotate in wheat or barley planted with no-till seeders. Minimising soil disturbance between potato crops could improve soil health and future potato yields.

A systems approach to improving soil health

According to the Soil Science Society of America’s, ultimately, growers need to take a systems approach to improving soil health with potatoes and with any crop. It is not just about one crop. It’s about how the whole cropping system is managed over time. By finding those intervention points to introduce a soil-building practice, growers can steadily improve soil health even with underground crops.