Feed the Future
This project is part of the U.S. Government's global hunger and food security initiative.

What’s the Payoff? Integrated Soil Fertility Management

This is part two of Dick Tinsley’s three-part series on smallholder limitations and oversights in development. Read part one here.

Applying the previous blog post on labor oversights in agronomy and development to the specific case of “integrated soil fertility”—with an emphasis on nutrient recovery and recycling—there are two problems:

  1. The supply of organic material needed for a commercial crop and;
  2. The labor needed to utilize it, including the recovery of the manual energy exerted.

Thus, this approach may fall into the category of easily demonstrated but non-extendable. That is, you can always come up with the materials and labor for a demonstration, but they will be quickly exhausted when extended across a community.

With regard to the supply of organic nutrients, the concern is that—with a grain crop—you are removing most of the nutrients when the grain is harvested. Thus, if you are planning to use the straw, etc., you have a 3 to 1 accumulating area for every unit of area to which it is applied. Now, how are you going to fertilize the 2 hectares from which you removed the crop residues? Similarly, if you are using manure from animals grazing on communal grazing lands, you need the manure from 4 animal units at 1.25 hectares per animal unit or 5 hectares of grazing land for each hectare to which it will be applied. Where can you find 5 hectares of grazing land for each hectare of cultivated land?

The labor is a more critical problem. Organic material is very bulky relative to its nutrient content. For smallholder communities, using organic material requires substantial manual time and physical exertion for the amount of nutrients recovered. This is compounded further when processed through composting. You have the labor needed to accumulate, the labor needed to process, and the labor needed to redistribute. All of this labor will most likely be heavy, in excess of 300 kcal/hour. This requires roughly 75 grams of milled maize or milled rice for each hour of effort. Unlike those of us puttering around home gardens with compost, but paying for most of our food from regular jobs, smallholders have to recover that energy from the yield increases generated from the recovered nutrients. Is this possible when the yield increase won’t be realized until the time of harvest—several months after the energy is expended? Can they wait that long to recover the energy exerted?

These "mobile composters" efficiently convert crop residue into a useful input.

Animal grazing is perhaps the most effective means of nutrient recovery and recycling. You might think of the animals as mobile composters. In fact, when comparing the soil microbes in compost to the ruminant microbes in an animal’s stomach, it’s clear that the processes are almost identical—and the latter is actually faster. Furthermore, even though the quality of the fodder is relatively poor, the animals actually extract energy in the process; whereas human labor requires energy expenditure. This grazing approach represents a convenient way of taking material that would have been otherwise burned prior to cultivation and converting it to something that is easily incorporated into the soil with tillage. Considering time and effort requirements, isn’t this likely to be the most cost-effective means of nutrient recovery and recycling?

Further Reading:


Dick Tinsley is an emeritus professor in the soil and crop sciences department at Colorado State University. He has over 30 years’ experience working with smallholder farmers and their communities, mostly in Asia and Africa. He summarized his career in the book “Developing Smallholder Agriculture: A Global Perspective." He also manages the website: www.smallholderagriculture.com