J.M. Herrera, N. Verhulst, R.M. Trethowan, P. Stamp and B. Govaerts
No tillage or zero tillage (NT) is the extreme form of reduced tillage; NT with residue retention is a main component of conservation agriculture. Using a literature survey and meta-analysis, this study aimed to (i) summarize the results of studies comparing the grain yield of wheat [Triticum aestivum L. and Triticum turgidum L. subsp. durum (Desf.) Husn. (syn. Triticum durum Desf.)] and maize (Zea mays L.) genotypes under contrasting tillage, (ii) identify sources of variation in the grain yield response of wheat and maize genotypes to tillage practices, and (iii) identify potential traits for NT breeding programs. Grain yield was compared under NT and conventional tillage (CT) for 112 wheat genotypes (44 spring, 60 winter, and eight durum wheat genotypes) across 12 locations and 24 yr and for 93 maize hybrids across six locations and 5 yr. Most of these studies showed slightly higher grain yields under CT for maize (+5%) and winter (+5%) and spring (+2%) wheat. In the few studies where selection had been conducted under NT, the effect of tillage on the grain yield was modified significantly by genotypes. Traits associated with the emergence of vigorous seedlings and resistance to a changed spectrum of diseases increase genotype performance under NT. There is a need to evaluate genotypes developed under NT and extend the research on genotype performance under NT to locations with reduced input use and, in addition to tillage, investigate other factors that differentiate conservation agriculture from conventional practice.
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