Abstract
• NPK fertilisation increased yield under irrigated conditions than in the rainfed. • NPK + secondary and micro-nutrients enhanced yield in the fluvisols not plintosols. • Secondary and micro-nutrients were effective only when NPK were applied. • Soil applied secondary and micro-nutrients with NPK was more effective than foliar. Rice is a staple food and cash crop for smallholder farmers in sub-Saharan Africa; however, yields are very low, with indications that both macro and micro-nutrients may limit rice productivity in East Africa next to the need for good agronomic practices. Diagnostic on-farm experiments were conducted in Uganda and Tanzania between 2015 and 2017 to assess the contribution of macro, secondary and micro-nutrients on lowland rice yield and identify options by which smallholder farmers can increase productivity. All treatments included good agronomic practices combined with: zero fertilisation as a control, NPK fertilisation with and without secondary and micro-nutrients (B, Mn, Zn, Cu, Mg, S), and/or treatments where B, Mn and Zn were omitted one at a time from the NPK + secondary and micro-nutrient treatment. NPK fertilisation significantly (p < 0.05) increased grain yield under irrigated condition by ca. 32 and 29 % during 2015 and 2016, and 24 and 100 % during 2016 and 2017 in Tanzania and Uganda, respectively; however, inconsistent effects were observed under rainfed condition. Observed higher yields corresponded mainly to higher panicle number with an additive effect of grains per panicle indicating major effects were at earlier growth stages supporting higher sink size development. Adding secondary and micro-nutrients to NPK enhanced yield significantly (p < 0.05) under irrigated condition in Tanzania 2015 and 2016 by 7 and 11 %, respectively, while varying results were obtained under rainfed condition. In Uganda, no significant (p> 0.22) effects of secondary and micro-nutrients were observed in both years and growing conditions. This study indicates that the first step to improving lowland rice productivity is proper water management, under otherwise also good crop management in terms of timely transplanting and weeding, and further yield gains can be realised with NPK fertilisation. Secondary and micro-nutrients were effective only when NPK were applied and on the fluvisols of Tanzania, and were not co-limiting yield on the plintosols of Uganda.
Highlights
Rice (Oryza sativa) is the most rapidly growing food commodity in sub-Saharan Africa (SSA) driven mainly by urbanisation and changing consumer preference (Seck et al, 2013), and plays a vital role in rural household food security and national economies (Nhamo et al, 2014)
This study indicates that the first step to improving lowland rice productivity is proper water management, under otherwise good crop management in terms of timely transplanting and weeding, and further yield gains can be realised with NPK fertilisation
This study has shown large yield gains with NPK fertilisation under good water and crop management, but with minimal yield gains under poor water management, even though good agronomic practices were followed
Summary
Rice (Oryza sativa) is the most rapidly growing food commodity in sub-Saharan Africa (SSA) driven mainly by urbanisation and changing consumer preference (Seck et al, 2013), and plays a vital role in rural household food security and national economies (Nhamo et al, 2014). Senthilku mar et al (2018), Rodenburg and Johnson (2009), Toure et al (2009), and Becker and Johnson (2001) recorded improved grain yields due to good agronomic practices - fine tillage, bunding, timely weeding and fertilisation, and attributed the gains to a lower weed biomass and increased use efficiency of applied fertiliser nutrients. While these studies report direct effects of good agronomic practices with or without fertiliser inputs on productivity, studies further show increase in yields with NPK application over nonapplication
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