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1. Crop residue mulch

Crop residues contain substantial quantities of plant nutrients. The data in Table 31 show the nutrient composition of the crop residues of some crops grown in the humid tropics. The concentration in oven-dry tissue ranges from 0.58% to 4.0% for N. 0.1% to 1.1% for P. and 0.2% to 3.4% for K. Nitrogen and phosphorus concentrations are generally higher in legumes than in cereals. On a weight basis, the major plant nutrients contained in 1 Mg of crop residue may range from 15 to 60 kg of N. P. and K (Table 32).

The beneficial effects of returning crop residue as mulch on crop yield are well known. These benefits are due not only to the recycling of plant nutrients but also to improvements in soil moisture and temperature regimes, enhancement of soil structure, and erosion control. However, the use of crop residues as fertilizers is especially important to resource-poor farmers. Some examples of the beneficial effects of crop residue mulch on crop yields are shown by the data in Tables 33 through 37. The data in Table 33 show that compared with an unmatched control, crop yields were improved with any mulch material. Rice husks increased maize yield by 0.7 Mg/ha and cassava yield by 12 Mg/ha. The data in Table 34 on yam production on an acid soil in eastern Nigeria show that mulching significantly increased the yam tuber yield. Mulching increased tuber yield by 20% on both ridge till and flat seedbed.

Table 31 Nutrient composition of crop residues of some crops grown in the humid tropics

(Modified from FAO, 1990)

Returning crop residue as mulch may also have synergistic effects with fertilizer use. The data from the eastern Amazon by Schoningh and Alkamper (1984) showed that crop residue mulches with low C:N ratios had more beneficial effects than those with high C:N ratios (Table 35). On an Ultisol in eastern Nigeria (Tables 36 and 37), the yield of plantain and bananas was drastically improved by residue mulch.

Table 32 Plant nutrients contained in 1 Mg of dry straw

(Recalculated from the data in Table 31)

Plantain yield was five times more with mulch than with chemical fertilizers alone. The data in Fig. 18 show that returning crop residue mulch enhanced the beneficial effects of fertilizer application in maize yield (Kang, 1993). Without fertilizer application, residue retention had little effect on maize grain yield.

Table 33 Crop yield response to 22 different mulch materials applied on Alfisols in Nigeria

Figures followed by similar Ietters are stastically similar within vertical roust (Okigbo and Lal. 1980)

Table 34 Effects of tillage methods and mulching on yield and yield components of yam tubers in eastern Nigeria

Figures followed by similar letters are statistically similar within vertical rows.

(Maduakor et al., 1984}

Table 35 Yield response of maize and cowpea to different mulch materials and mineral fertilizer in an eastern Amazon Oxisol, Capitao Poco (CPATU) Para, Brazil, 1983

* Grain moisture content 14. 5%
** Grain moisture content 13, %

(Schoningh and Alkamper 1984)

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