Tropical soils degraded by slash‐and‐burn cultivation can be recultivated when amended with ashes and compost

Abstract

In many tropical regions, slash-and-burn agriculture is considered as a driver of deforestation; the forest is converted into agricultural land by cutting and burning the trees.However, the fields are abandoned after few years because of yield decrease and weed invasion. Consequently, new surfaces are regularly cleared from the primary forest. We propose a reclamation strategy for abandoned fields allowing and sustaining re-cultivation. In the dry region of south-western Madagascar, we tested, according to a split-plot design, an alternative selective slash-and-burn cultivation technique coupled with compost amendment on 30-year-old abandoned fields. Corn plants (Zea mays L.) were grown on four different types of soil amendments: no amendment (control), compost, ashes (as in traditional slash-and-burn cultivation), and compost + ashes additions. Furthermore, two tree cover treatments were applied: 0% tree cover (as in traditional slash-and-burn cultivation) and 50% tree cover (selective slash-and-burn).Both corn growth and soil fertility parameters were monitored during the growing season 2015 up to final harvest. The amendment compost + ashes strongly increased corn yield, which was multiplied by 4-5 in comparison with ashes or compost alone, reaching 1.5 t/ha compared to 0.25 and 0.35 t/ha for ashes and compost, respectively. On control plots, yield was negligible as expected on these degraded soils.Structural equation modeling evidenced that compost and ashes were complementary fertilizing pathways promoting soil fertility through positive effects on soil moisture, pH, organic matter, and microbial activity. Concerning the tree cover treatment, yield was reduced on shaded plots (50% tree cover) compared to sunny plots (0% tree cover) for all soil amendments, except ashes. To conclude, our results provide empirical evidence on the potential of recultivating tropical degraded soils with compost and ashes. This would help mitigating deforestation of the primary forest by increasing lifespan of agricultural lands. K E Y W O R D Scrop yield, deforestation, microbial activity, organic matter, soil fertility, structural equation model | 5379 GAY-DES-COMBES Et Al.

Oil palm ‘slash-and-burn’ practice increases post-fire greenhouse gas emissions and nutrient concentrations in burnt regions of an agricultural tropical peatland

“…The decrease in nutrient concentrations after few months may be because some of the nutrients are highly prone to leaching (Beliveau et al, 2015;Ulery et al, 1993). Similar increase immediately after a fire was also observed for other physico-chemical characteristics such as pH and electrical conductivity because of the addition of ash (Bang-Andreasen et al, 2017;Gay-Des-Combes et al, 2017), before reverting back to normal over time (Kutiel and Naveh, 1987). Fire may also effect increased mineralisation indirectly through soil microbial processes (Gay- Des-Combes et al, 2017).…”

A new hypothesis for the origin of Amazonian Dark Earths

“…The addition of charcoal can slow down Ca loss but leaching rates of 50–150 kg Ca ha − 1 year -1 have been reported in charcoal-rich ADE profiles 60 . Moreover, P losses are expected to be slower than for Ca, although large amounts of P can be lost in fine particulate form as a result of burning—a practice often attributed to ADE formation 61 . If we were to account for those losses, the total amount of waste needed to form the 12-ha ADE patch at our site would be orders of magnitude larger than those presented here.…”

Do topography and fruit presence influence occurrence and intensity of crop-raiding by forest elephants (Loxodonta africana cyclotis)?

“…Forests cover 97% of the landscape (65% of the area occurs in logging concessions, 18% in the park) and 3% is dedicated to traditional slash and burn agriculture (TSBA) [ 14 , 27 ]. In TSBA, trees and brush are cut to convert forest to agricultural land, and the resulting slash is burned to amend the soil [ 28 ]. Fruit-producing trees are left standing and serve as non-timber forest products (NTFP).…”

“…In addition to fruiting trees, evergreen tropical rain forest is present in the study site and near the farms [ 14 , 27 ]. After 2 to 4 years of agriculture, farmers abandon old fields and restart the process [ 28 ]. In MCNP, crop species mainly consist of bananas ( Musa sp .)…”