Determinants of fertilizer microdose-induced yield increment of pearl millet on an acid sandy soil.
Recent studies have reported the benefits of fertilizer microdosing in increasing crop yields in low input cropping systems. Little information is however available on the mechanisms underlying this effect. The objective of this study was therefore to explore the root-based mechanisms governing the growth enhancing phenomena of the fertilizer microdosing technology. A two-year experiment was conducted at the International CropsResearch Institute for the Semi-AridTropics (ICRISAT),Research Station in Niger. Four treatments comprising (i) 2 g hill1 of diammonuim phosphate (DAP), (ii) 6 g hill1 of compound fertilizer NPK, (iii) broadcasting of 200 kg ha1 of compound fertilizer NPK (recommended rate) and (iv) unfertilized control was arranged in a randomized complete block design with four replications. On average, fertilizer microdosing treatments (2-g DAP hill1 and 6-g NPK hill1) achieved 86% and 79% of the grain yields recorded from broadcasting of 200-kg NPK ha1, respectively, in 2013 and 2014. The leaf area index and leaf chlorophyll content significantly increased with fertilizer microdosing at the early stage of millet growth. At the same stage, fertilizer microdosing enhanced the lateral root length density in the topsoil (020 cm) by 72% and 40% at respective lateral distances of 25 cm and 50 cm from the centre of the hill compared with broadcast of 200-kg NPK ha1. Fertilizer microdosing did not significantly change soil pH in the root zone. It is concluded that the positive effect of fertilizer microdosing in increasing millet yield results from the better exploitation of soil nutrients due to early lateral roots proliferation within the topsoil.