Agri‐Mat Mulching Improves Aggregate Stability and Soil Pore Formation on Smallholder Farms in Sub‐Saharan Africa

ABSTRACT

Agri‐mats are solid organic mulch mats derived from various organic waste materials such as straw, grass, weed biomass, algae residues, etc. These agri‐mats are created by hot‐ or cold‐pressing biomass into solid, bio degradable mats. Although agri‐mats provide remarkable benefits to agricultural soils, including improved soil fertility and crop productivity, their effect on topsoil structure has not been adequately explored. The aim of this study was to determine the aggregate stability and physical architecture of two contrasting soils using the fast‐wetting method and X‐ray microfocus computed tomography (CT), respectively. The following five treatments were established in two sites (Durban with loam soil and Pretoria with sandy loam soil): (i) full agri‐mat cover (100% AG), (ii) half agri‐mat cover (50% AG), (iii) bare or no cover (control), (iv). 6 tons.ha⁻¹ of grass mulch (6 t.GM) and (v) 3 tons.ha⁻¹ grass mulch (3 t.GM). The two sites were planted with maize in summer and spinach in winter for two consecutive seasons (2017/18 and 2018/19). The aggregate stability test results indicated that 100% agri‐mat (100% AG) mulch had greater aggregate stabilizing ability than all other mulching treatments in both soil types. In the loam soil, the 100% AG treatment increased the stability of the aggregates by 58% and by 65% in the sandy loam soil after two years. The X‐ray CT analysis results showed that under the loam soil, 50% AG mulch treatment produced more (89%) macro‐aggregates (> 250 μm) compared to 100% AG (77%). However, the 100% AG treatment produced more (71%) macro‐aggregates compared with the 50% AG (65%) under the sandy loam soil. Based on the overall morphological characteristics of the soil aggregates, the 100% AG treatment was superior to the other organic mulching treatments in terms of soil pore structure formation and aggregate stability regardless of the soil type after two years.