Conservation tillage and biochar improve soil water content and moderate soil temperature in a tropical Acrisol
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Date
2020
Journal Title
Journal ISSN
Volume Title
Publisher
Soil and Tillage Research
Abstract
Projected climate change in Sub-Saharan Africa involves increased drought and elevated soil temperature.
Conservation farming (CF), including minimum tillage, crop rotation and crop residue retention, is proposed as a
climate smart soil management option to adapt to climate change through enhanced climate resilience. Here, we
determine the effect on soil moisture and temperature of CF planting basins in a Zambian Acrisol. Construction
of CF planting basins (40 cm x 15 cm, while 20 cm deep), using hand-hoes, is a commonly used minimum tillage
practice among small holders in southern Africa, effectively requiring tillage of only 10 % of a field. The study
included basins under regular CF and under CF with 4 t ha−1 pigeon pea biochar (CF+BC). Effects are compared
with those in an adjacent soil under conventional tillage, where the entire land surface is ploughed. Soil
moisture and temperature sensors were installed in the root zone, 10–12 cm deep, for continuous monitoring
during two growing seasons. Soil moisture decreased in the order CF+BC > CF > conventional farming. Due
to rainwater harvesting in the basins, maximum soil water retention under CF+BC and CF was greater than
under conventional farming (+59 % to +107 % and +15 % to +65 %, respectively). Soil drying after free
drainage until permanent wilting point lasted longer under CF+BC (18.4–22.3 days) than under both CF and
conventional farming (13.3–18.4 days and 14.9–17.8 days, respectively). In situ soil maximum temperature and
diurnal temperature range in the growing season increased in the order CF+BC < CF < conventional farming
due to decreases in soil moisture. However, additional laboratory tests, with soil-BC mixtures at field capacity,
revealed that BC addition to soil, which caused a decrease in bulk density, also resulted in a significant decline in
soil thermal conductivity (p < 0.001). Thus, we hypothesize that BC-enhanced soil moisture in basins helped to
reduce soil temperature and its fluctuations, due to both increased heat capacity and decreased thermal conductivity.
This study shows that CF in combination with BC in an Acrisol, through enhancing plant-available
water and moderating soil temperature, is important for crop productivity and has potential as an element of
climate smart agriculture.
Description
Keywords
Planting basins, Biochar, Soil water retention and temperature
Citation
Obia, A., Cornelissen, G., Martinsen, V., Smebye, A. B., & Mulder, J. (2020). Conservation tillage and biochar improve soil water content and moderate soil temperature in a tropical Acrisol. Soil and Tillage Research, 197, 104521.