Application of secondary nutrients and micronutrients increases crop yields in sub-Saharan Africa

Abstract

Secondary and micronutrients are important in enhancing crop productivity; yet, they are hardly studied in sub-Sahara Africa. In this region, the main focus has been on macronutrients but there is emerging though scattered evidence of crop productivity limitations by the secondary and micronutrients. Elsewhere, widespread deficiencies of these nutrients are associated with stagnation of yields. Here, we undertake a meta-analysis using 40 articles reporting crop response to secondary and micronutrients to (1) determine the productivity increase of crops and nutrient use efficiency associated with these nutrients, and (2) provide synthesis of responses to secondary nutrients and micronutrients in sub-Sahara Africa. This study used 757 yield data rows (530 from publications and 227 from Africa Soil Information Service) from field trials carried out in SSA between 1969 and 2013 in 14 countries. Data from publications constituted response to S (49.4%), Zn (23.0%), S and micronutrient combinations (11.5%), and <10% each for Cu, Mo, Fe, and B. Data from Africa Soil Information Service were all for S and micronutrient combinations. Of the two sources, most yield data are for maize (73.6%), followed by sorghum (6.7%) and wheat (6.1%) while rice, cowpea, faba bean, tef, and soybean each accounted for less than 5%. The major points are the following: (1) application of S and micronutrients increased maize yield by 0.84 t ha −1 (i.e., 25%) over macronutrient only treatment and achieved agronomic efficiencies (kilograms of grain increase per kilogram of micronutrient added) between 38 and 432 and (2) response ratios were >1 for S and all micronutrients, i.e., the probability of response ratio exceeding 1 was 0.77 for S and 0.83 for Zn, 0.95 for Cu, and 0.92 for Fe, and indicates positive crop response for a majority of farmers. We conclude that S and micronutrients are holding back crop productivity especially on soils where response to macronutrients is low and that more research is needed to unravel conditions under which application of S and micronutrients may pose financial risks.

Does gypsum increase crop grain yield on no‐tilled acid soils? A meta‐analysis

“…The positive effect of gypsum application was less marked under the less critical plant growth conditions (i.e., the absence of water deficiency and low Al saturation in the subsoil) ( Figure 5). Similar results were obtained for the response to S and micronutrients of crops on African soils (Kihara et al, 2017). However, gypsum application slightly increased grain yield even under favorable conditions for crop growth here ( Figure 5…”

“…The procedure involved calculating the natural logarithm of the response ratio for grain yield at each gypsum rate used. After confirming that the vast majority of primary studies included in the meta-analysis exhibited no data dispersion in terms of variance, SD, and SEM, observations were weighted according to number of replicates (n) as shown in Equation 1 (Kihara et al, 2017;Pittelkow et al, 2015):…”

“…where GY treatment and GY control (Mg ha −1 ) are the crop grain yields obtained with and without gypsum application, respectively. As recommended by Kihara et al (2017), following calculation of the means and their 95% CIs, the probability of a given effect on grain yield resulting from gypsum application was calculated by generating the frequency distribution of the effect of gypsum on crop grain yield in each subgroup and calculating the cumulative probability of the effect occurring.…”

“…This negative effect may increase with the decrease of CEC of the soil. Cereal grain yield increased by 2.4% on average even in soils with Al saturation <5%, possibly because gypsum is a source of SO 4 2− -S for crops and because sulfur is a macronutrient that increases the probability of a positive crop response in tropical and subtropical soils (Kihara et al, 2017;Pias, Tiecher, Cherubin, Mazurana, & Bayer, 2019).…”

“…Answering these questions may help farmers and consultants adopt and improve gypsum application in NT soils (Dalla Nora et al, 2017b;Soratto & Crusciol, 2008a). In addition, establishing specific criteria for gypsum management based on experiments conducted mainly in Brazil may help extend its use to other tropical or subtropical regions (e.g., Latin America, Africa) with naturally acid and low-fertility subsoils (Kihara et al, 2017), although some regional research is necessary. In this work, we conducted a meta-analysis to assess the response of grain crops to gypsum application in NT soils.…”