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September 20, 2012

Feed the Soil, Feed the Crops

by Joe DeCapua

If African farmers are going to feed the continent, they may first want to feed the soil. Studies show farmland is often depleted of vital nutrients. But researchers say a combination of organic farming methods may help.



Since the global food crisis several years ago, greater investment is being made in smallholder farms. Most of the farms in sub-Saharan Africa are smallholder, consisting of about one or two hectares. One of the goals is to boost yields without necessarily clearing more land to grow additional crops.

Washington State University researchers say that can happen with greater use of an agricultural system called perenniation. It mixes food crops with trees and perennial plants. Soil scientist John Reganold co-wrote an article about it in the journal Nature.

“This system that we call perenniation is one of those systems where you actually plant perennials and it increases both food security and it builds the soil at the same time,” he said.

There’s an old saying that you are what you eat. Plants need nourishment, too, and they get it from the soil.

He said, “One of the major problems is that the soils are fairly poor in most of the regions. And so how do you grow food on poor soils? There have to be food production systems that can build the soil and improve the yield.”

Reganold said that poor soil may have resulted from years of weathering that leaches many of the nutrients. But in some cases farmers may have done more harm than good.

“They have been actually using farming practices where they’re not putting in organic matter. They’re not putting in fertilizers. They can’t afford those things. And it just runs the soil down more. So they’re actually mining the soil. So they’re worsening the situation,” he said.

He said that the major nutrients that farmland needs are nitrogen, phosphorous and potassium.

“The big one,” he said, “is nitrogen. That’s the nutrient that the plant demands the most and that’s the fertilizer that’s mostly needed.”

He estimated that up to two billion dollars worth of nitrogen, phosphorous and potassium is lost from African soil each year.

That’s where perenniation comes in. It adds nutrients back into the soil.

“We came up with the term perenniation, but the systems have been around for a while. We use the term perenniation. It defines three systems that are already used in Africa. The oldest of the three is called evergreen agriculture and it’s where farmers actually plant trees with their crops. And they’ve been doing this to the best of my knowledge for 60 years, but it’s starting to gain ground,” he said.

It’s gaining widespread use in countries such as Niger, Burkina Faso, Malawi and Zambia, among others. The trees are planted among maize, millet or sorghum. They not only add nitrogen to the soil through their roots, but also through their leaves when they fall off and decay. At other times of the year the trees can shade plants from the harsh sun. Reganold said colonial English and French farmers believed crops should be separated from trees, not mixed together.

Besides planting trees, the perenniation also calls for the use of the doubled-up and the push-pull systems. The doubled-up system has farmers mixing pigeon pea plants among soybean and maize crops. Pigeon pea, a large shrub, adds nutrients to the soil, but can later be used for fuel and fodder. Some parts are edible.

The push-pull system also uses perennials, such as napier grass, which is grown around the maize, and desmodium, which is planted among the stalks. Reganold says desmodium 
is a natural pest management system. It pushes away the stem bore moth from the crops, while the napier grass pulls or lures the moth to the perimeter of the crops. Thus push / pull.

Reganold gave an example of one woman who had great success with perenniation.

“She’s a grandmother in her 50s. Her name is Rhoda Mang’yana and she started using this system about 20 years ago. She used actually two of the systems – the doubled-up legume and she also started using these evergreen agriculture trees. And her yields initially were about a ton of maize per hectare. Now with a good year she gets four tons per hectare. Four times what she was getting,” he said.

Reganold and his colleagues said millions of dollars should be invested in perenniation each year. He hopes development NGOs will take up the cause. Reganold co-wrote the Nature article with Jerry Glover of USAID and Cindy Cox of the International Food Policy Research Institute.