Influence of mulching materials on soil temperature, moisture and crop productivity

Abstract:

Practical dilemma: a farmer near Windhoek deciding what to lay between tomato rows this season faces a choice between plastic film that costs money every season, straw that costs nothing but decomposes within months, and leaving the soil bare, a choice this two-season research set out to inform with direct comparative data rather than convention alone. Four soil surface treatments, plastic mulch, straw mulch, organic leaf litter mulch, and bare soil (no mulch), were compared for their effect on soil temperature, soil moisture retention, weed suppression, and tomato yield. Bare soil recorded the highest and most variable soil temperature, averaging 34 °C at 5 cm depth during peak afternoon hours, against 26 °C under organic leaf litter mulch and 27 °C under straw mulch, while plastic mulch, despite its dark color absorbing more radiant heat, still moderated peak temperature to 31 °C relative to bare soil through reduced evaporative moisture loss. Soil moisture retention followed a similar pattern, with plastic mulch conserving the most moisture overall at 38.4% share of total moisture retained across treatments, though organic and straw mulches conserved moisture more efficiently relative to their input cost. Tomato yield was highest under plastic mulch at 3420 kg per hectare, 27.6% above bare soil, followed by straw mulch and organic leaf litter mulch, both delivering meaningful yield gains over bare soil at a fraction of plastic mulch's material cost. These findings support mulching broadly as a productivity-positive practice regardless of material choice, while highlighting that the specific material selected should weigh moisture conservation efficiency, cost, and local material availability together rather than assuming plastic mulch's yield advantage alone justifies its higher cost in every farming context.