Dust mulch and in-situ moisture conservation Photo: Cemil Gokmen · Pexels License · source ↗

Dust mulch and in-situ moisture conservation

Dust mulching is a traditional dryland tillage practice in which the topmost 3-5 cm of soil is broken up after each rainfall event into a fine, loose layer that acts as a thermal and capillary barrier above the moist sub-surface. It is the oldest documented in-situ moisture-conservation technique used by farmers across the semi-arid tracts of peninsular India, including the Rayalaseema, Telangana, northern Karnataka and Marathwada belts. ICAR-CRIDA and ICAR-Indian Institute of Soil and Water Conservation (IISWC) have validated its agronomic basis and incorporated it into the standard dryland package for groundnut, sorghum, redgram and other rainfed crops.

Principle

After a rainfall event, soil moisture is held in the wetted profile and is lost mainly by upward capillary movement to the surface where it evaporates. Capillary rise depends on a continuous network of fine pores connecting the wet sub-surface to the dry surface; this network re-forms within hours of soil drying and accelerates moisture loss. Breaking the top 3-5 cm into a loose granular layer disrupts the capillary network at the air-soil interface. The loose layer also acts as a thermal insulator, lowering soil temperature 3-5 deg C at 5 cm depth and reducing evaporative demand. The net effect is a 20-40 mm seasonal saving in evaporation from the root zone.

Procedure

The standard package for groundnut and other rainfed crops in Anantapur:

Pre-sowing: deep summer ploughing to 25-30 cm during April-May to break sub-soil hard pans and store pre-monsoon showers.
Sowing layout: sow on the contour or on raised beds to facilitate run-off harvesting in furrows.
Inter-row cultivation: at 20-25 DAS and 35-45 DAS, run a tined cultivator or bullock-drawn blade harrow across the rows to break the soil crust to 3-5 cm depth and bury surface weeds. Each operation creates a fresh dust mulch.
Post-rain operations: within 24-48 hours of each significant rainfall event (>15 mm), repeat the shallow cultivation if the crop is still small enough. Once the crop canopy closes (typically 50-60 DAS in groundnut), shading replaces the dust mulch as the dominant evaporation suppressor.
Combined with organic mulch: where crop residue is available, surface application of 3-5 t/ha of paddy straw, groundnut shells or sorghum stover (Mulching Organic Residue) provides a more durable barrier than dust mulch alone.

Where and when it applies

Dust mulching is most effective in coarse-textured red soils and light sandy loams where capillary rise is rapid and crust formation is severe. It is appropriate for rainfed crops with row-spacing wide enough to allow mechanical inter-row cultivation (groundnut 30 cm rows; redgram 60 cm; sorghum 45 cm). The practice is suited to the early-vegetative phase of the crop (15-50 DAS) before canopy closure. It is most useful in years with intermittent rainfall - long dry spells with occasional heavy events - which is the typical Anantapur kharif pattern.

Limitations

Dust mulch is destroyed by heavy rainfall and must be reformed after each event - this is labour-intensive without animal-drawn or tractor-drawn equipment. The practice does not work after canopy closure when row-running is no longer possible. On vertisols and other heavy soils, dust mulch formation is difficult because the soil aggregates are too large to break into a fine layer. The practice is also incompatible with no-till and conservation-agriculture systems that prioritise residue retention. Where labour and bullock power are scarce, custom-hiring of tractor-mounted blade harrows (Custom Hiring Machinery) is the practical adaptation.

Sources

In-situ moisture conservation in dryland agriculture. ICAR-Central Research Institute for Dryland Agriculture.
Soil and water conservation in drylands. ICAR-Indian Institute of Soil and Water Conservation.
Dust mulch and soil mulching. PJTSAU dryland package.