Assessing the potential options for improving crop yield and water use efficiency in the sahelian low input millet-based cropping system

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
Soil amendments are often unavailable in adequate quantities for increased crop production in the Sahelian smallholder cereal cropping systems. In order to increase crop yields and encourage farmers to apply inorganic fertilizers, fertilizer micro-dosing technology was developed. This technology has given promising results in respect of crop yields improvement, fertilizer use efficiency and economic returns. However, many scientific reports have cautioned that crop nutrients uptake under micro-dosing technology could be markedly greater than what was applied through the technology. There, is therefore, an urgent need for critical assessment of the potential mining effect of fertilizer micro-dosing in order to develop supportive strategies for further improvement of the efficient use of limited resources of smallholder farmers. The objectives of this study were to (1) explore the mechanisms governing the growth enhancing phenomena of the fertilizer micro-dosing technology, (2) assess the potential effects of integrated use of organic amendments and fertilizer micro-dosing in improving millet yield and water use efficiency and (3) evaluate the extent of nutrient gains and losses under fertilizer micro-dosing by estimating the associated nutrient balances. To achieve these objectives, three field experiments were conducted in Niger during the 2013 and 2014 rainy seasons. The first experiment comprised two options of fertilizer micro-doing (2 g DAP hill-1 and 6 g NPK hill-1) with the broadcast of 200 kg NPK ha-1 which is the blanket recommended rate of fertilizer in the study area. The second experiment consisted of the factorial combination of two fertilizer micro-dosing options with three rates of manure (1000 kg ha-1, 2000 kg ha-1 and 3000 kg ha-1) and method of their applications (hill placement and broadcasting). The third experiment involved two fertilizer micro-dosing options and three organic mulches (millet straw, Acacia tumida pruning and manure). The most important findings that emerged from these experiments were that growth parameters (leaf area index, leaf chlorophyll content and root length density) were markedly increased with fertilizer micro-dosing at the early stage of millet growth compared with the broadcast of 200 kg NPK ha-1. The millet grain yield under fertilizer micro-dosing combined with manure increased on average by 59%, 83% and 113% for 1000 kg ha-1, 2000 kg ha-1 and 3000 kg ha-1 of manure inputs, respectively in comparison with fertilizer micro-dosing alone. These increases in grain yield were accompanied by marked increases in water use efficiency. Hill placement of manure increased total dry matter on average by 23% and water use efficiency by 35% relative to that of manure broadcasting. The partial nutrient balances were -37 kg N ha-1yr-1, -1 kg P ha-1yr-1, -34 kg K ha-1yr-1 in plots that received the application of 2 g DAP hill-1 and -31 kg N ha-1yr-1, -1 kg P ha-1yr-1, -27 kg K ha-1yr-1 for the 6 g NPK hill-1 treatment. The partial nutrient balances were exacerbated by the nutrient export in straw yields which accounted for on average 66% N, 55% P and 89% K of total export. The annual full nutrient balances with fertilizer micro-dosing treatments were on average - 47 kg N ha-1 yr-1, -7 kg P ha-1 yr-1 and -22 kg K ha-1 yr-1 which represented 7%, 24% and 10% of N, P and K stocks, respectively. Combined application of fertilizer micro-dosing with organic mulch increased millet grain yield by 37%. The millet grain yield increases relative to the un-mulched control were 51% for manure, 46% for A. tumida mulch and 36% for millet mulch. The addition of A. tumida pruning, manure and millet straw mulch to fertilizer micro-dosing increased water use efficiency of millet by on average 55%, 49% and 25%, respectively. These results indicate that the positive effect of fertilizer micro-dosing in increasing millet yield results from the better exploitation of soil nutrients due to early lateral roots proliferation within the topsoil. In addition, millet production with the fertilizer micro-dosing technology can be improved further by hill-placement of manure. However, the increase in yields with fertilizer micro-dosing was accompanied by an increase in soil nutrients uptake which resulted in negative nutrient balances. These results have important implications for developing an agro-ecological approach to address sustainable food production in the Sahelian smallholder cropping systems.
A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, in fulfilment of the requirements for the award of degree of Doctor of Philosophy in Soil Science, 2015