1. Mulch farming

Mulch is a layer of crop residue placed on the soil surface. There are different types of mulches, depending on the source and method of mulch procurement and application (Fig. 13). The technological methods of mulch farming differ on the basis of whether mulch is brought in or produced in situ. Although a wide range of materials is used as mulch, the most practical and feasible material is the residue from a previously grown crop. The beneficial effects of mulching are attributed to:

(i) physical effects that minimize raindrop impact, improve rainfall acceptance through enhancement of soil structure and reduce runoff and erosion;

(ii) biological effects that increase the activity and species diversity of soil flora and fauna, notably earthworms increased biomass carbon, and improved crop growth; and

(iii) chemical effects that alter nutrient status and influence crop growth.

Fig. 13 Different types of mulch materials and associated agricultural practices

A principal benefit of mulch farming is reduction in runoff and soil erosion. The data in Table 13 from slopes of 1% to 15%, show that a mulch rate of 4 Mg/ha effectively reduced runoff even on a 15%, slope. The data in Table 14 show the negative value of the exponent of mulch rate (M), indicating that runoff and soil erosion decrease exponentially with an increase in mulch rate even without a crop cover. In addition to increasing the infiltration rate, mulch also decreases soil evaporation and conserves water in the root zone. The major limitations lie in the large quantities of residues required (usually 4 Mg/ha/yr) for regular and frequent applications economic uses of mulch (as fodder, fuels or construction material) and the additional cost of labor involved in mulch procurement and application. Consequently, mulch farming is likely to be feasible on a small scale for high-value commercial crops.

Table 13 Effect of mulch rate on runoff on different slopes

(mm)
Slope (%)	Mulch rate (Mg/ha)
	0	2	4	6	No tillage
First season runoff (April July)
1	283 6	4	0	6
5	346 61	10	7	9
10	219 46	21	12	15
1 5	294 47	20	12	14
Second season runoff (August November)
1	129	30	3	0	5
5	137	65	18	4	6
10	84	28	14	9	9
15	80	40	31	8	9

* Rainfall first season 510 mm second season 249 mm.
(Lal, 1976)

A tillage system that ensures a maximum retention of crop residue on the soil surface is called mulch tillage or stubble mulch farming. It is defined as a method of seedbed preparation that involves leaving crop residues or other mulching materials on or near the surface. When a grain crop is seeded through the mulch of a chemically killed cover crop, it is called sod seeding. If the cover is only suppressed temporarily or not killed, the system is called live mulch. A cover crop, usually a legume, is grown specifically to break the cropping cycle, to produce mulch material, to improve soil structures and to enhance soil organic matter content.

Table 14 Mulch rate effects on runoff and soil loss for an Alfisol on different slope gradients

Slope (%)	Regression equation	Correlation coefficient
Runoff
1	0.78	R = 0.39 M -9.73
5	0.80	R = 1.16 M -0.36
10	0.86	R = 5.53 M -0.27
15	0.75	R = 5.26 M -0.55
Soil erosion
1	0.85	R = 0.19 M -0.54
5	0.85	R = 1.25 M -0.71
10	0.96	R = 1.09 M -0.67
15	0.72	R = 0.98 M -0.24

M = Mulch rate in Mg/ha
R -- Mean annual runoff (mm)
(Lal. 1976)