Rice Yield Gaps in Smallholder Systems of the Kilombero Floodplain in Tanzania

Abstract

To meet the growing rice demand in Africa, gaps between actual and attainable yields have to be reduced. In Tanzania, this particularly concerns smallholder rain-fed production systems in the floodplains. After quantifying the existing yield gaps, key contributing factors need to be analyzed to improve site-specific management. Field experiments were conducted for three years and in three pedo-hydrological environments (fringe, middle, and center positions) of the Kilombero floodplain to evaluate: (1) The grain yield under farmers’ management (actual yield), (2) yield with the best-recommended management (attainable yield), and (3) the non-limited yield simulated by the APSIM model (potential yield). In the field, we additionally assessed incremental effects of (1) field bunding and soil levelling, (2 and 3) additionally applying of 60 kg N ha−1, as urea or as farmyard manure (FYM), and (4 and 5) incorporating in-situ-grown leguminous green manures. Attainable yields were determined with mineral N application at 120 kg ha−1, additional PK fertilizer and supplemental irrigation. On average across years and positions, the potential, the attainable, and farmers’ actual yields were 11.5, 8.5, and 2.8 t ha−1 indicating a high total yield gap. About 16–38%, 11–20%, and 28–42% of this gap could be attributed to non-controllable yield-reducing (i.e., pest and diseases), yield-limiting (i.e., water and nutrient deficiencies), and yield-defining factors (i.e., poor soil and crop management), respectively. Results indicate a closure of the exploitable yield gap (differences between attainable and farmers’ actual yields) by up to 6.5 t ha−1 (nearly 60% of the potential yield). This exploitable yield gap was larger in 2016 than in 2017. Also, the gap was larger in the water-limited fringe and middle than in the frequently submerged center positions. Simple field bunds combined with land levelling could close 15–35% of the exploitable yield gap, depending on field positions and year. FYM or green manures were less effective than mineral N; however, in 2017 and in the wetter middle and center positions, they reduced the yield gap by >50%. We conclude that yield gaps in rainfed rice in Kilombero floodplain are large, but that a site- and system-specific adaptation of crop management can close much of the exploitable yield gap and increase grain yields by 0.7–4.8 t ha−1. Similar benefits may be obtained in other hydrologically variable floodplain environments of the region and beyond.

Assessing the effects of management and hydro-edaphic conditions on rice in contrasting East African wetlands using experimental and modelling approaches

“…Similar findings have been reported from inland valleys in the Indonesia and Thailand (Boling et al, 2008), and India (Cornish et al, 2020). Meanwhile, attainable yields of > 7.2 Mg ha − 1 in the floodplain and of about 5.2 Mg ha − 1 in the inland valley, were still substantially lower than simulated yield potentials of up to 10.5 and 7.3 Mg ha − 1 in the floodplain and inland valley, respectively (Kwesiga et al, 2020b). Overall higher yields and yield responses to applied N fertiliser in the floodplain as compared to the inland valley were associated to more favourable rainfall and hydro-edaphic conditions and varietal differences, i.e., greater inherent yield potentials of the lowland rice cv.…”

Monitoring and Analyzing Yield Gap in Africa through Soil Attribute Best Management Using Remote Sensing Approaches: A Review

“…Modeling can range from simple climate indices such as Fischer's photothermal coefficient to intermediate models such as AquaCrop and the more complex CERES-type models. For instance, a study was conducted recently in Tanzania [32] that used the Agricultural Production Systems Simulator (i.e., APSIM) model to estimate the yield gap and investigate its variations in rice culture in the Kilombero floodplains region. Here, three yield levels were measured: (i) current yield, (ii) yield with the most recommended management (i.e., attainable yield), and (iii) potential yield.…”

Assessing Opportunities to Increase Yield and Profit in Rainfed Lowland Rice Systems in Indonesia

“…The attainable yield values are consistent with those reported by [2,52] for simulated water-limited yield potential for rainfed lowland rice in Indonesia. According to [53], the difference between simulated potential and average farmers' current practices is the total yield gap. This comprises yield-defining factors that are difficult to control, such as water supply from precipitation, soil properties, nutrients, weeds and some pests and diseases.…”