Friday, July 3, 2009

Zai Holes

Zai holes are used in arid country to wring a crop out of the land. It is obvious that past cropping has destroyed the soil’s integrity and has made this extreme step necessary.

However the effort produces a successful planting, however much it looks like a pot.

It also shows that these are potential seed hills and that water retention is also possible. Adding a good supply of biochar should make these beds sustainable and long lived allowing the investment to be maintained and recovered many times.

Constantly adding biochar over many seasons should also expand the soil base over an increasing area and slowly loosen up the clays.

This also gives us an appreciation of the labor necessary to convert a mere hectare into usable farm land from badly damaged soils. Obviously the rainy season provides ample water, but left to itself in theses soils, it would all escape in runoff.

Farmers know how to use manures including composts, but have never before understood how to prevent their reduction in the soil and loss. Biochar is able to manage that issue.

Do read the letter from bakery who has hands of experience and is improving his operation is Ghana.

Mali and Burkina Faso's Farmers apply the Zaï technique to recover crusted land in semi-arid regions.

Zaï is a hole, a planting pit with a diameter of 20-40 cm and a depth of 10-20 cm - the dimensions vary according to the type of soil. Pits are dug during the dry season from November until May and the number of Zaï pits per hectare varies from 12,000 to 25,000.(The number of zaï per hectare and their dimensions determine how much water they harvest. The bigger the number and the smaller their size, the less water they harvest.)The excavated earth is ridged around the demi-circle to improve the water retention capacity of the pit.

After digging the pits, composted organic matter is added at an average, recommended rate of 0.6 kg/pit and, after the first rainfall, the matter is covered with a thin layer of soil and the seeds placed in the middle of the pit.

Zaï fulfils three functions: soil and water conservation and erosion control for encrusted soils. The advantages of Zaï are that it :

captures rain and surface/ run-off water;
protects seeds and organic matter against being washed away;
concentrates nutrient and water availability at the beginning of the rainy season;
increases yields; and
Reactivates biological activities in the soil and eventually leads to an improvement in soil structure.

The manure applied to the pits contains seeds of trees or bushes. This helps the regeneration of the vegetation on fields treated with pits.

The application of the Zaï technique can reportedly increase production by up to 500% if properly executed.


High labour to dig the zai holes ( between 300 and 450 hours/hectare)
High maintenance labour (in soils with a high clay or gravel portion, pits require less maintenance than pits dug in sandier soils.)
No mechanization possible.
The pits should be dug during the dry season.
Size and position are important.
Composted organic material should be used, not raw organic material.

And this report from Bakary Jatta helps put this in perspective and updates developing practice.

Dear TP enthusiasts,

After finding out about the Zai hole practice, I immediately adopted the practice in combination with using biochar. It solved the problem of having to produce the large quantities of char required to cover the entire area. Increased crop production and restoring soil fertility are priorities in our society in my opinion. Sequestering CO2 is not an immediate survival issue for the average person here even when aware of the climate issue.

With the resulting increased biomass, the process will accelerate in time. I am combining several soil improvement methods at the same time. I like to point out that stopping soil erosion using low contour bunds fortified with Vetiver grass is probably sequestering CO2 faster than biochar or tree planting. The Vetiver roots penetrate soil up to three meters within a year depending on soil and wheather conditions.

Than inter cropping with selected tree species will increase and extend the process into the future. It amounts to a modified form of Permaculture, I think.

The labor intensity is spread over a longer time as the dry season does not prevent one from digging holes altogether, depending on one’s will and/or stamina. Leaving the soil covered with crop residue slows down the hardening of the soil considerably. I am looking forward to the soil structure becoming easier to work as time goes on. The previous biochar applications have shown that effect to a notable degree.

I am very pleased to find out I did not waste my energy.

Kind regards to all,

Bakary Jatta

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