Abstract
Residue burning to prepare soil for maize growing deprives the soil of both protective cover and organic matter, and it exacerbates environmental issues such as Southeast Asia's haze problem. This paper reports on a study that evaluated the effectiveness of maize/legume intercropping as an alternative to maize cultivation with residue burning. Cowpea (Vigna unguiculata), mung bean (V. radiata), rice bean (V. umbellata), and lablab (Lablab purpureus) were sown into a standing maize crop 30 days before harvest, and the results were compared with a maize crop grown using residue burning as the method for land preparation at Pang Da Agricultural Station in Chiang Mai, Thailand, in a replicated trial conducted over 3 growing seasons from 2012 to 2014. Intercropping increased maize grain yield by 31–53% and left 70–170% more residue containing 113–230% more nitrogen than the maize sown after residue burning, depending on the legume, and decreased weed dry weight by two-thirds after 2 seasons. Soil biodiversity was enriched by the intercrops, with a doubling in the spore density of arbuscular mycorrhizal fungi in the root-zone soil and increased abundance, diversity (Shannon index), and richness of the soil macrofauna. The abundance of soil animals increased with crop residue dry weight (r = 0.90, P < 0.05) and nitrogen content (r = 0.98, P < 0.01). The effect of intercropping on maize grain yield and accumulation of residue and nitrogen were then confirmed in a participatory experiment involving farmers in 2 highland villages in the Phrao and Chiang Dao districts of Chiang Mai Province with maize and rice bean in 2015. The effects of maize/legume intercropping—increased nitrogen accumulation and crop residue, enhanced soil biodiversity, suppression of weeds, and protection of the soil surface, which enabled the maize to be sown without land clearing with fire—should all contribute to sustainable highland maize production.
Highlights
Slash-and-burn agriculture, a traditional practice in the mountains of Southeast Asia, was once the main method for producing the opium cash crop as well as subsistence crops (Kunstadter et al 1978; Mertz et al 2009)
This paper reports on 2 experiments: (1) a field experiment to evaluate intercropping maize with rice bean, cowpea, lablab, and mung bean as an alternative to maize cultivation with residue burning as well as the impact of intercropping on biodiversity in the soil; and (2) a participatory experiment comparing the performance of intercropped maize and rice bean with maize sown after residue burning grown by the same farmers
Over the 3 years of the experiment, grain yield of intercropped maize averaged 53% higher than that of maize sown after residue burning when the legume was lablab and 33% higher with rice bean, cowpea, and mung bean
Summary
Slash-and-burn agriculture, a traditional practice in the mountains of Southeast Asia, was once the main method for producing the opium cash crop as well as subsistence crops (Kunstadter et al 1978; Mertz et al 2009). Maize in the highlands is grown by first cutting down existing vegetation in the field and burning it before sowing This is different from maize production in the lowlands—where land is ploughed to prepare it for sowing—and is problematic in a number of ways. It contributes to haze and very high concentrations of atmospheric particulate matter, which peaked at more than 4 times the safety standard of 120 lg PM10 (particulate matter diameter that is 10 lm or smaller and inhalable) per cubic meter in March and April 2012 in Chiang Rai, Chiang Mai, and Nan (Pollution Control Department 2017), highland provinces at the center of maize production with residue burning in the mountainous region of mainland Southeast Asia as well as within Thailand
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