Nutrient deficiencies limit rice production in sub-Saharan Africa. The conventional recommended remedy for this is the soil application of fertilizers composed of the macro-nutrients, N, P and K, whereas crop micronutrient requirements are neglected. This leads to nutrient mining and diminished fertiliser use efficiency. Application of micronutrients along with recommended NPK fertiliser rates can prevent nutrient mining and boost rice yields. In this study, we assessed the productivity and profitability of different soil- and foliar-applied micronutrients in 30 on-farm trials per year for two consecutive years (2015, 2016) in Tanzania, East Africa. Five locally available foliar formulations (combinations of macro- and micronutrients or micronutrients alone) and soil application of micronutrients (3−2−7.5−10 Zn-B-Mg-S kg ha^–1) were assessed under two NPK-fertilization regimes (80−17.5−33.2 and 0−0−0 kg N-P-K ha^–1) in three rice growing environments (RGEs): Irrigated Lowland (IL), Rainfed Lowland (RL), and Rainfed Upland (RU). The effect of foliar and soil applied micronutrients on yield was consistent in IL but was highly variable in the RL and RU conditions across years. The soil application of micronutrients in the absence of NPK was ineffective in any of the RGEs. In IL, without NPK, foliar application alone increased yield by 0.3−0.4 t ha^–1, compared to control (3.1 t ha^–1). Only NPK application increased yield by 1 t ha^–1, while NPK and micronutrients application increased yield by 1.5 t ha^–1, compared to control. The benefit-cost (B:C) ratio for NPK with soil applied micronutrients was 4–4.5 compared to NPK application alone. In RL, application of NPK alone increased yield in 2015 from 2.7 to 5.0 t ha^–1 while NPK and soil applied micronutrients application increased yield to 6.8 t ha^–1. However, a drought incidence in 2016 nullified this effect. With NPK, two foliar products (F2 and F3) increased yield significantly by 1 t ha^–1. The highest B:C ratio was obtained with soil applied micronutrients (B:C of 14), and two of the foliar products obtained a B:C ratio of 7 and 7.2, respectively. In RU, no significant yield differences were observed among treatments in any year, likely due to drought. Foliar application was effective only under drought-free conditions across the rice growing environments. This study demonstrated that soil applied micronutrients together with NPK significantly increased yields in IL and RL in the absence of drought-stress. Application of macronutrients is a likely prerequisite for maximizing the benefits of applying micronutrients to increase rice yields in Tanzania.

营养缺乏限制了撒哈拉以南非洲的水稻生产。对此，传统推荐的补救措施是在土壤中施用由大量营养素、N、P 和 K 组成的肥料，而忽略作物微量营养素的需求。这导致养分开采和肥料使用效率降低。微量营养素的应用以及推荐的 NPK 肥料用量可以防止营养挖掘并提高水稻产量。在这项研究中，我们在东非坦桑尼亚连续两年（2015 年、2016 年）每年进行 30 次农场试验，评估了不同土壤和叶面施用微量营养素的生产力和盈利能力。五种当地可用的叶面配方（宏量和微量营养素的组合或单独的微量营养素）和微量营养素的土壤施用（3-2-7.5-10 Zn-B-Mg-S kg ha^–1 )在三种水稻生长环境 (RGE) 中的两种 NPK 施肥制度（80-17.5-33.2 和 0-0-0 kg NPK ha ^–1）下进行评估：灌溉低地 (IL)、雨养低地 (RL)、和雨养高地（RU）。叶面和土壤施用微量营养素对产​​量的影响在 IL 中是一致的，但在 RL 和 RU 条件下跨年变化很大。在没有 NPK 的情况下土壤微量营养素的应用在任何 RGE 中都是无效的。在没有 NPK 的 IL 中，与对照（3.1 t ha ^–1）相比，单独叶面喷施使产量增加了 0.3-0.4 t ha ^–1。仅施用 NPK 可增加 1 t ha ^–1产量，而施用 NPK 和微量营养素可增加 1.5 t ha ^–1产量，与对照相比。与单独施用 NPK 相比，施用土壤微量营养素的 NPK 的效益成本 (B:C) 比为 4-4.5。在 RL 中，仅施用 NPK 就将 2015 年的产量从 2.7 t ha ^–1提高到 5.0 t ha ^{–1 ，}而施用 NPK 和土壤微量营养素将产量提高到 6.8 t ha ^–1。然而，2016 年的干旱事件抵消了这种影响。使用 NPK，两种叶面产品（F2 和 F3）显着增加了 1 t ha ^{–1 的}产量. 土壤施用微量营养素（B:C 为 14）可获得最高 B:C 比，两种叶面产品的 B:C 比分别为 7 和 7.2。在 RU 中，任何年份的处理之间都没有观察到显着的产量差异，这可能是由于干旱。叶面喷施仅在整个水稻生长环境中的无干旱条件下才有效。该研究表明，在没有干旱胁迫的情况下，土壤施用微量营养素和 NPK 显着提高了 IL 和 RL 的产量。在坦桑尼亚，宏量营养素的应用可能是最大限度地利用微量营养素提高水稻产量的先决条件。