Rapid reconaissance finished

What do soils in the five sectors of Bulungu territory look like? And how do the differences affect recommendations for soil-building legumes and agroforestry projects? Those questions have preoccupied part of the ACDI team for nearly 5 weeks now. They were the questions that drew two teams of extension agents off on rapid reconnaissance trips covering well 1000 kilometers and collecting over 350 observations.

Maybe what we learned is not all that surprising. Soil profiles tend to be deep and usually free from hard impermeable layers. Color varies from very light, dusky browns on the sandy soils of the plateaus to vivid hues of yellow and red in the valley soils. Texture ranges from almost pure sand (again on the plateaus of Kilunda, Luniungu and Mikwi sectors) to slick, slightly expansive clays, particularly near the Kwilu River. But most soils are basically sandy with a modest measure of clay. Sandy soils support grass savanna and brushy or woodland savanna. Loamy and clay soils support brush and forest - with land cover very heavily influenced by the history of agricultural use. (Finding an intact primary forest or even old secondary forest in the territory is very difficult these days.)

People here are tied to the forest. They clear and cultivate land that has been lying fallow for several years, grown back to dense, scrubby brush with occasional tall trees. They depend on this natural cycle of regeneration to renew soil fertility.

The mineral soil itself is poor to dismal. Highly weathered, acid, exerting a weak hold on nutrients. Fertility depends almost entirely on the vigor of the vegetation; the mineral nutrients that sustain growth are all locked up in the vegetation, roots, and soil organic matter. Like a plant nutrient mine. Exploited every 4 or 5 years.

Mines reach a point where extraction costs surpass the production value. Forest treated in the same way, with no effort to restore nutrients, works the same way. It is not sustainable. That's where many farmers in Bulungu find themselves now. Sustainability requires replacing the nutrients one extracts. Fertilizers cost money that people don't have. The resource-poor farmer turns to plants that collect nitrogen from the atmosphere or essential nutrients slowly released in the deep soil. Rotted leaves, roots, trunks and other organic matter provide good nutrient storage.

Our observations over the last five weeks show that soils generally have good physical structure and a balance between good drainage and reasonably good water-holding capacity. The key to success is managing fallow vegetation and organic matter. The challenge is to produce more with considerably less -- land and length of fallow period.

We now have a clearer idea of where we can try leguminous cover crops and crop rotations that include woodlots. And increasingly the international aid projects in Bandundu are open to underwriting experiments in sustainable agriculture.