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Wheat ( Triticum aestivum L.) is the third most important crop in Ethiopia yet its productivity in the country remains significantly below experimental yields and water-limited yield potential due to soil fertility variability and the absence of site-specific fertilizer recommendations. To identify yield-limiting nutrients and support the development of a precision fertilizer recommendation tool, a nutrient omission study was conducted in the 2021 main cropping season across eight sites in the South Gondar Zone of Northwestern Ethiopia. The study evaluated eight treatments: (1) NF (NPKSZnB), (2) -B, (3) -Zn, (4) -S, (5) -K, (6) -P, (7) -N, and (8) F0, with nutrients applied at 138 kg N, 46 kg P2O5, 60 kg K2O, 10.5 kg S, 5 kg Zn, and 1 kg B ha -1 . Results indicated that N omission significantly reduced wheat yield and yield-related traits across all sites, while P limitation was significant in 50% of the locations. The average yield response to N application was 2071.9 kg ha -1 (ranging from 847.2 to 2873.6 kg ha -1 ), followed by P, with a mean response of 499.1 kg ha -1 (16.6–850.8 kg ha -1 ). Soil indigenous nutrient supply (SINS) assessments revealed that N was only 45.0% sufficient, whereas P sufficiency was higher (87.0%). Potassium (K), sulfur (S), zinc (Zn), and boron (B) were found to be non-limiting, with soil supplies exceeding 90%. Yield gaps due to N and P omission averaged 53.9% and 11.9%, respectively, while omissions of K, S, Zn, and B had negligible effects. Agronomic efficiency was highest for P (22.2 kg kg -1 ), followed by N (13.1 kg kg -1 ) and K (5.2 kg kg -1 ). These findings demonstrate that N is the primary yield-limiting nutrient in the study area, with P being secondary in half of the evaluated farms. To enhance wheat productivity and minimize yield gaps, site-specific fertilizer recommendations emphasizing optimized N and P application are critical. The study was conducted for one season, and hence multi-year experiments to address season variation on the effect of the nutrient omission treatments is recommended.

The potential yield of improved maize varieties usually cannot be fully realised mainly due to inappropriate soil nutrient management practices in most parts of Ethiopia. Site-specific fertiliser recommendations are rarely used in the farming systems of Ethiopia. There is also a lack of data to develop or validate decision support tools for targeting specific crop production. A study was conducted for three consecutive rainy seasons (2016–2018) in the maize belt of the north-western parts of the Amhara National Regional State of Ethiopia. The objectives were to obtain the maximum achievable yield potential of maize, determine the most yield-limiting nutrients and create a database of maize responses to applied nutrients so that decision support tools could be developed for the study areas. Treatments were individual nutrients (nitrogen (N), phosphorus (P) and potassium (K)) and combinations of the three. In some treatments, NPK was also combined with sulphur, zinc, lime and compost. Two hybrid maize varieties (BH-540 and BH-660) adaptable to the study areas were used. BH-540 was used for the Mecha district, while BH-660 was used for the south Achefer, Jabitahnan–Burrie–Womberma districts. Maize yield increased by more than 50% due to fertiliser applications compared to without fertiliser. The study showed that the possibility of increasing maize productivity to more than 12 t ha-1 for the study sites. The most yield-limiting nutrient in the study sites was N, followed by P; K was not a yield limiting. Without N the yield of both varieties was non-significant from the control (without added nutrients). Maize grain yield did not respond to application of lime, compost, zinc and sulphur. The result also showed very high variability across sites, indicating that it is important for policymakers, farmers and investors to consider site-specific fertiliser recommendations. Finally, a database containing intensive plant response to NPK for maize was generated and could be used as input in site-specific decision support tools development.

Soil provides crop with nutrients, water and root support. But, soils vary a great deal in terms of origin, appearance, characteristics and production capacity. Better understanding of the causality between yield and yield-limiting soil factor(s) is essential for site-specific crop management. The objectives of this study were deriving a spatiotemporal yield trend map of a 144 km 2 paddy rice growing region located at an alluvial plain in southwestern Taiwan from satellite images and exploring the potential yield-limiting soil factor(s) in conjunction with general soil survey data. Due to the complexity of data sets, classification and regression trees analysis (CART) was used to relate soil characteristics to yield classes in the spatiotemporal yield trend map, and followed by comparisons of soil characteristics between those consistently-high and -low yielding areas to explore the interactions between yields and soil properties. Through the above data mining analysis, high soil pH, severe leaching loss of applied nitrogen fertilizers, and excessive reductive root environment were suspected to be the major soil related low-yielding mechanisms spread within studied region. Soil characteristics that induced these low-yielding mechanisms were identified and mapped. Error analysis indicated that 61.8 % of the consistently low-yield areas could be correctly identified by just a few soil characteristics. Improvements of management practices to alleviate the negative effects on yields were also proposed based on the identified low yielding mechanisms. Our study highlighted the pressing need and possible methodologies to adjust management strategies for narrowing yield variability and increasing crop production.