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Chapter 9

Producing Fortified Compost from Crop Residues

Keziah W. Ndung’u, Mary N. Kifuko and J. Robert Okalebo

Many African countries continue to require increasing amount of food aid (World Bank, 1996) because their agricultural production does not match population growth. This is most evident in countries where population growth is very high and yet soils tend to be highly weathered and have low inherent fertility (Smaling et al., 1997). In Kenya, farmers realize the need for soil amendments by using available resources such as farmyard manure, poultry wastes and piggery effluent (Woomer and Swift, 1994), however, the quantity and quality of these materials limit their use (Delve, 1998). In addition, farmers appreciate the use of mineral fertilizers but their ever-increasing costs often prohibit their application at recommended rates (Heisey and Mwangi 1996). In some areas, crop residues such as wheat straw and maize stovers are left on the land but their decomposition rate is very low because of the high C:N ratio. These materials accumulate in very large amounts and are difficult to dispose. For example, in Uasin Gishu and Trans Nzoia districts of Kenya, yields of maize stover and wheat straw range from 4 to 15 t ha^-1 (Muasya, 1996). Management of these residues includes incorporation back into the soil, feeding residues to livestock or burning (Lwayo et al., 2001). The Faculty of Agriculture at Moi University has developed a technology to recycle plant nutrients from wheat straw and maize stover. This technology involves fortification of these residues with nitrogen (N) and phosphorus (P) fertilizers to reduce losses from the composting process.

Procedure for Fortification of Organic Residues

Low quality organic materials such as maize stover or wheat straw with a wide C/N ratio are suitable for preparing fortified compost. The procedure for fortifying such organic materials is:

1. Chop crop residues into 30-45 cm lengths in order to increase their surface area.

2. Spread the chopped material in five successive layers of 30 cm high by 2.0 m wide into windrows 25 m long (» 500 kg in each layer).

3. At every 30 cm layer, evenly broadcast 3.75 kg DAP (or any other nitrogen-bearing fertilizer) for fortification lowering the C:N ratio from 80 to about 12.

4. Apply 1.0 kg of organic soil uniformly as a “starter inoculant”. Farmyard manure, sugarcane mill filter mud or pond sediments are suitable materials for this purpose.

5. Apply 20 litres of water at the same height to enhance dissolution of fertilizers and to moisten the stover for microbial activity.

6. Repeat steps 1 to 5 until the 25 m windrows are 1.5 m in height (Figure1).

Turning the Compost

Turning compost is important as it ensures proper mixing, wetting, aeration and decomposition. The compost heap is allowed to settle for one month, and then turned using pitch forks. Material on the top of the heap and along the edges is laid on the ground first, followed by the materials in the middle of the heap. Materials at the bottom are then placed at the top of the heap. It is recommended to sprinkle 20 liters of water on the heap during turning particularly when conditions are dry. Compost turning is continued until the heaped materials turn dark gray. Biological activity is monitored by pushing a stick into the middle and sides of the stack. The stick is pulled periodically and felt by hand for any temperature changes. For example, eight days after compost piling, much heat is generated from the center of the heap and the stick driven in the compost should indicate the same. This is an indication of biological activity in the compost (e.g. the thermophilic stage). Composting requires 4 to 6 months and at maturity and about 1900 kg of fortified compost is produced. Mature compost is odourless and has a fine texture. When the stick for testing temperature is driven into the heap, it should be cool (at ambient temperature) indicating that all the potentially harmful organisms and by-products have been eliminated.

Table 1. Sources and characteristics of commonly available crop residues, compost and manure among smallhold farmers in western Kenya

Chemical Properties and Use

A comparison between fortified compost and a number of crop residues and organic manures appears in Table 1.  Fortified compost is consistently among the highest organic resources in terms of nitrogen (2.2%), phosphorus (0.42%), potassium (1.42%) and organic matter (52%).

Significant maize grain yields from fortified compost applied at 2 t ha^-1 were observed as compared to the control (Figure 2). Fortified compost provided 4 t ha^-1 of grain yield, which was comparable to DAP at 20 kg P per ha, probably due to the increased N and P release from the compost. Non-fortified compost applied in conjunction with DAP at 20 kg P ha^-1 resulted in reduced yields, demonstrating better agronomic effectiveness of fortified compost compared to an alternative allocation of the same inputs. In areas with large quantities of maize stover, fortifying these residues is an alternative to burning.

Conclusion

There is potentially a large number of farmers in western Kenya who could benefit from the use of fortified compost to improve their overall crop yields and better utilize post harvest residues. The technology offers potential to smallhold sugar outgrowers in western Kenya as well as large-scale and wheat producers in the Rift Valley. The mound and windrow composting technique described in this chapter is appropriate for materials other than maize stover and wheat straw and when higher quality materials such as manure, tree prunings and grass cuttings are being composted, there is little or no need to fortify them with mineral fertilizer. However, lack of technical know-how to make and use compost is lacking. Farmers should be trained on how to prepare fortified compost. On-farm trials should be conducted at multiple locations to enable as many farmers as possible to learn how to make and use fortified compost. Socio-economic factors, such as labor availability or lack of space, that hamper the adoption of this technology should also be identified and solutions to these problems offered.

References

Delve, R.J. 1998. Implications of Livestock Feeding Management on Soil Fertility in Smallholder Farming Systems. Ph.D Thesis, University of London.

Heisey, P.W. and Mwangi, W. 1996. Fertilizer Use and Maize Production in Sub- Saharan Africa. CIMMYT Economics Working Paper 96-01, CIMMYT, Mexico.

Lwayo-Kisaka, M., Okalebo, J.R., Muasya, R.M. and Mongare, P.O. 2001. a diagnostic survey on the utilization of phosphate fortified wheat straw and maize stover compost for increasing cereal production in Uasin Gishu District, Kenya. A KARI-ARF-Moi University Report, Eldoret, Kenya. 106 pp.

Muasya, R.M. 1996. Wheat Responses to Fortified Wheat Straw Compost, M.Ph. Thesis, Moi University, Eldoret, Kenya.

Smaling, E.M.A., Nandwa, S.M. and Janssen, B.H. 1997. Soil Fertility in Africa is at Stake pp. 47-61. In: R.J. Buresh, P.A. Sanchez and F. Calhoun (Eds.), Replenishing Soil Fertility in Africa. SSSA Special Soil Publication No. 51, SSSA, Madison Wisconsin, USA.

Woomer, P.L. and Swift, M.J. (Eds.). 1994. Biological Management of Tropical Soil Fertility. John Wiley and Sons, Chichester, UK.

World Bank. 1996. Natural Resource Degradation in Sub-Saharan Africa: Restoring of Soil Fertility in Africa. The World Bank, Washington D.C.

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