Surface mulching effects on soil temperature of jumbo-size potted coarse-textured Ultisols and evaluation on sorghum and soybean growth

Abstract

In poticulture, surface mulching to conserve moisture is rarely practised even when it could help elongate watering intervals, while moderating soil temperature and crop growth, benefits of which are potentially huge when large volumes of drought-prone soils are involved. This study compared, under glasshouse conditions, mulched and no-mulch jumbo-size potted droughty Ultisols for differences in soil temperature, soil structure, and sorghum (Sorghum bicolor) and soybean (Glycine max) growth responses. After layer-wise filling of the 63-cm high 123.75-L jumbo-size pots to the 60-cm mark using excavated 40-60, 20-40 and 0-20 cm soil layers, mixed dry grass was surface-applied at 10 t ha^–1 equivalent. Sorghum and soybean were grown separately in mulched and no-mulch potted soils for two nine-week cycles. Soil thermal and agronomic data were collected weekly at certain growth stages, while soil structure was assessed after the second cycle. Soil temperature was always lower in mulched than no-mulch potted soils, being significant at four and eight sampling times for sorghum and soybean, respectively. Plant height of sorghum was consistently unaffected by the mulch treatment; however, mulched potted soils produced higher above-soil dry matter than the no-mulch ones (87 vs 49 g pot^–1 ) in the second cycle. By contrast, soybean plants were always shorter and dry matter lower (11 vs 34 g pot^–1 ) due to mulching in the first cycle; plant height response was reversed in the second, being evident during the last three weeks. Notably, both crops grew better in the second than the first cycle. Mulching only tended to improve soil structure under both crops. The mulch-induced increases in sorghum above-soil dry matter were, however, due to cooler soil temperature-driven enhanced aggregation; the reverse effect in soybean was due to cooler soil temperatures. Our data suggest that grass mulch-induced lowering of temperature of large-volume potted drought-prone soils would have pronounced positive and negative influence, respectively, on productivity of cereal and leguminous crops. Considering the initial tillage-like disturbance of such potted media, this influence, for soil structure-sensitive cereals, is largely due to temperature-mediated temporal enhancement of aggregation.