The effectiveness of vegetative mulches against evaporation may be limited unless they are thick to a sufficient diameter because their high porosity permits rapid diffu­sion and air currents. The initial rate of evaporation under mulch is reduced so water is saved if rainfall is frequent. But, in case of extended periods of dry spells, mulch may keep the surface of soil moist and hence prolong the first stage of evaporation, thus producing no net saving of water (Hillel 2007) . With the cane harvest via mechanical ways without burning, the addition of straw on the surface of soil is responsible for the reduction in the soil evaporation, increase in the content of water for plant transpiration, and hence improvement of the efficiency of water usage (Ball-Coelho et al. 1993; Chapman et al. 2001).

Since the surface of soil is completely covered with sugarcane for 60-90 days after emergence of shoot, mulching mostly affects evaporation/transpiration during the first 90 days. Peculiar to this, requirement of water for sugarcane is more sig­nificant during the first period of the cycle, i. e., tillering, sprouting, and establish­ment, whereas during the vegetative growth period, there is a decrease in water demand becoming negligible during maturation period (Leal et al. 2013). Chapman et al. (2001) confirmed this pattern with field trials when the loss of water was similar for both green (unburned) and burned canes in late growth, while the loss of water from soil in early growth under green cane was only 32 % of that from burned cane.

Many studies were conducted with the aim to quantify and correlate the benefits of mulch on crop yield. Ball-Coelho et al. (1993) measured higher water content of soil in the mulched plots in the Goiana experiment in Brazil, which was apparently related to higher soil micropore space, due to activity of higher plants and fungi in the presence of layer of litter. The yield of harvestable cane of first ratoon crop was 17 mg ha-1, with the 70 % content of moisture, greater in mulch than in the treat­ment of burned cane. This response of yield is attributed to increased water retention of soil and reduced growth of weed under the mulch.

Tominaga et al. (2002) also measured higher content of soil water in sugarcane without burning of straw, compared to plots burned before harvest and bare soil control plots. The simulation of production of stalk of sugarcane in South Africa using APSIM model indicated that the higher production observed in unburned management was related to the higher content of soil water (Thorburn et al. 2007).

According to a study, the use of sugarcane straw around 0.1 m thick cover spread on interrow spaces is the most practical way to increase the effectiveness of irrigation by reduction in the loss via evaporation from the surface of soil by capillary rise. The straw maintained the moisture at a higher level for a relatively longer time com­pared to uncovered soil surface (Shrivastava and Solomon 2011). The conclusion drawn from this study is that maintenance is responsible for increase in yield by 10 % for systems under irrigation. In another study, water loss in terms of percent­age was quantified in the upper layer of soil (0-0.2 m). It was determined that with­out the treatment of straw, the loss of water was 0.45 mm/day, while with the treatment of straw, it was 0.21 mm/day (Peres et al. 2010).

Another interesting aspect is the use of vertical mulch — a modification of sub­soiling, in which organic materials, such as straw and filter cake, or inorganic mate­rials, such as gypsum and sand, are inserted in the slot created by the subsoiler (Garcia 2005). Howell and Pheen (1983) tested the benefits of vertical mulch in irrigation studies concluding that it was responsible for intake of water resulting in 25 % increase in cotton yield in California. In the fields of sugarcane, the use of vertical mulching is responsible for increase in the effective rooting depth, hence improved intake of water, greater hydraulic flow, and increased capacity of available moisture (Meyer et al. 1992).

Among all the aspects raised, the increased infiltration and lower evaporation in the presence of straw mulch, compared to bare soil, is an advantage regarding pro­duction of stalk, mainly in areas where irrigation is not being practiced thus there is high deficit of water in the period of vegetation growth.