Performance of Foxtail Millet Varieties Under Varying Row Spacing in Semi-Arid Alfisols

Abstract

Foxtail millet (Setaria italica) is a short-duration, drought-tolerant cereal that suits the rainfed Alfisols of the semi-arid tropics, and row spacing is one of the cheapest agronomic levers available to the farmers who grow it. Recommendations for spacing are nonetheless inconsistent, and varieties are often advised the same geometry regardless of their architecture. This narrative review asks what the published literature can and cannot say about the performance of foxtail millet varieties under different row spacings on semi-arid Alfisols, and it reports no new data. It draws on work on the biology and tillering of foxtail millet, on the physics of water and radiation capture in sparse canopies, on the long-standing theory of plant population and yield, and on the statistics of genotype-by-environment trials. The central difficulty is that the best spacing is not a property of the crop alone: it shifts with variety, with the amount and timing of rainfall, and with soil fertility, while most field trials come from a single site and a single season and so confound these influences. Wide rows tend to favour stored water and tillering where rain is scarce, and narrow rows favour early canopy closure and weed suppression where it is not, but the crossover point is poorly characterised. The review closes with the design features that a convincing multi-season, multi-site spacing trial would need.