Context and objective Improving rice yield and resource-use efficiency is essential for sustainable crop intensification. This study quantified the magnitude and causes of rice yield gaps in irrigated lowland production systems of southern Brazil. Methods We combined observations from 475 farmer fields collected over five growing seasons (2016–2020) with the process-based crop model SimulArroz and stochastic frontier analysis to estimate potential yield, actual yield, and the contributions of genetic, environmental, and management factors to the overall yield gap. Results Mean potential yield was 16.0 t ha⁻¹ , whereas farmers' actual yield averaged 8.4 t ha⁻¹ , resulting in an overall yield gap of 7.6 t ha⁻¹ . The genetic component (cultivar choice) explained approximately 10% of the total yield gap, whereas environmental effects associated with sowing date accounted for 20%. The remaining yield gap was primarily associated with management, with the resource (46%) and efficiency (24%) yield gap components representing the largest opportunities for improvement. Optimizing sowing date alone could increase regional rice production by 8.4%, equivalent to an additional 0.5 Mt of paddy rice, without expanding cultivated land. Conclusions and significance Management practices remain the main leverage point for narrowing rice yield gaps in southern Brazil. Site-specific optimization of sowing date, nutrient management, and crop establishment can substantially improve productivity and resource-use efficiency, supporting sustainable intensification of irrigated rice production systems.
Context and objective Rice (Oryza sativa L.) grain chalkiness is a serious problem under high temperature (HT) and/or low solar radiation. The degree of chalkiness varies among grains within a panicle. However, the spatial and temporal patterns of chalkiness within a panicle and the underlying mechanisms causing this variation remain unclear. Methods In this study, the temperature-sensitive mutant flo11–2 and wild-type cultivars were used to elucidate the distribution of chalkiness ratio and grain area within a panicle under four short-daylength treatments and three nitrogen levels over three years. A two-day HT treatment was applied to examine spatial and temporal changes in susceptibility to chalkiness during grain filling. Results and conclusions Grain area, a possible indicator of available carbohydrates per spikelet, was greater at the upper and middle positions of each primary rachis branch (PB), regardless of the PB position within a panicle. In contrast, the distribution of chalkiness ratio differed markedly from that of grain area and changed progressively from the upper grains of the top PB to the lower grains of the bottom PB under short-daylength treatments that covered a wider range of grain-filling periods. Nitrogen fertilizer treatments conducted over three years further showed that the upper grain position (G1) had a significantly larger grain area than the lower grain position (G7), whereas the upper branch position (B1) exhibited a significantly higher chalkiness ratio than the lower branch position (B10). Because grain sensitivity to HT varied, being higher at 13–14 days after flowering (DAF) than at 21–22 DAF, the distribution of chalkiness ratio could be influenced by how this sensitive period coincided with HT. Significance Rice grain chalkiness is more strongly influenced by flowering order than by carbohydrate supply, which was demonstrated for the first time through the use of the temperature-sensitive mutant flo11–2.
Context and Objective Soil erosion is a major threat to smallholder farming systems in Rwanda. Terraces, while effective, are costly and reduce cultivable land area. Conservation agriculture (CA) offers a promising complementary practice if short-term yield penalties relative to current tillage (CT) remain acceptable to farmers. We assessed the seasonal and cumulative yield performance of a CA system relative to CT, farmers’ perceptions of soil erosion control under CA, and the site-level conditions under which CA yields remain within farmer-acceptable bounds. Methods A CA system combining reduced tillage, intercropped cover crops, and residue retention in a maize–bean rotation was evaluated over six cropping seasons (three years) across 473 farms in ten agroecological zones of Rwanda. A farmer-informed threshold for acceptable CA yield performance (CA:CT yield ratio ≥ 0.90) was derived from the empirical relationship between observed yield ratios and farmers' stated adoption intentions. Random forest models were used to identify site-level drivers of CA performance, and to inform a targeting approach based on observable field characteristics. Results and conclusions On average, CA yields were 19% lower than CT for maize and 24% lower for beans, yet farmers consistently perceived erosion reduction under CA, highlighting a trade-off between short-term yield penalties and longer-term soil protection. The amount of mulch cover at planting, accumulated rainfall, and weed pressure were the key drivers of CA performance. Site-level targeting increased the probability of achieving acceptable yield performance from 30% to 50%, though only ~20% of sites were initially identified as suitable for CA. Site-level targeting offers a realistic pathway to managing the trade-off between short-term yield penalties and longer-term soil protection benefits of CA. Significance This study demonstrates that scaling complex, system-based agronomic technologies in heterogeneous farming environments requires moving beyond average treatment effects. Co-defined performance thresholds and the identification of context-specific drivers can improve targeting but are insufficient on their own. We argue that combining these with adaptive dissemination strategies is necessary to offer a more realistic pathway to impact. The targeting framework developed here is directly applicable by extension programs in Rwanda, and provides a replicable model for other complex, system-based agricultural innovations.
