Zai: Experimental Design

Now that you have an idea of what Zai are, here's what we're doing with them in South Africa.

Sorghum growing in Zai (all pictures of growth are 3 months after planting)

Our Zai field has 5,760 holes and mounds, all hand dug, manured, planted, and when we can help it, hand weeded. It takes about a week to have 8 day laborers casually weed it. Glyphosate use may be in our future, but thus far none of our experiments here have used generic Roundup due to the fact that we are mostly interested in two things: looking at the changes in soil fertility and soil biology. Since labor is abundant and inexpensive here, we have the luxury to side with the research that suggests glyphosate negatively affects soil biology and thus we weed all our plots with hoes and scuffle boards.

Horsegram residue after a full dry season

Sorghum plot without legumes

This is the third and possibly last season for this experiment. In it we have examined changes in soil fertility and biology, and also soil moisture, yield (grain and pulse), biomass amount and nutrient contents, all through 15 treatments over time. We look at the effect of manure that is concentrated vs. broadcast; the effect of preplant vs. split manure application; the effect of flat ground vs. Zai; the effect of a solid grain plot vs. a legume-intercropped plot; the effects of 4 different legume intercrops.

Horsegram intercrop

Cowpea and pigeon pea intercrop

In all the Zai plots we planted Sorghum bicolor 'Macia'. Sorghum is a grain that looks much like maize until it flowers. Its grain is all in a head on the top of the plant and is known for being drought tolerant, an important trait in places with low or erratic rain. Sorghum is intercropped in legume treatments with 1.) Lablab purpureus 'Highworth', 2.) Vigna ungiculata 'IT98D-1399' [Black-eyed pea/cowpea], 3.) Macrotyloma uniflorum [Horsegram], and 4.) Cajanus cajans 'Caqui' [Pigeon pea] with cowpea.

Zai covered in Lablab residue before the season shown above

Not quantified in research is the value of mulch beyond its contribution to soil nutrients. The sorghum plots that were intercropped with legumes had the added benefit of having residue that protected the soil from harsh winds for about 5 months during the dry season. When building soil in semi-arid regions, every bit of organic matter counts. In days the small fraction of carbon that is being stored long-term in the soil could be blown away. If the residue is thick enough, it will also suppress weed growth when the rains come.

Zai might not be very stable here without soil crusting, but the results suggest some of its principles are working anyway in improving the soil. It will be exciting to see what some of these values become after a third season, and the possibility for small famers to find a season of plenty, slowly increasing over time.

Efficacy? Success? For specific results, please visit ECHO Community, where you can get free resources for tropical agriculture, information on agriculture development technologies and techniques, request seeds, and more.

Januario setting the wire to dig the next row of Zai