Site-specific Fertilizer Recommendations Research Articles

A new approach to measure spatial variability of soil parameters and field technique to test-value specific fertilizer recommendations

<p>Information on the distribution of soil properties is important to know the status of nutrients in the soils based on which fertilizer nutrients are recommended. Given the variability of nutrients in the soils, making a site-specific fertilizer recommendation seems to be a compelling work. To determine the spatial variability of soil nutrients and to make judicious and precise fertilizer recommendations, new measures are designed with this study. These measures are tested against the soil samples (n = 43) for total nitrogen (N), organic matter (OM), phosphorus (P2O5), and potassium (K2O) in the study area. The descriptive statistical analysis indicated an average of low nitrogen and organic matter, while phosphorus was found to be very high and the level of potassium was high. The spread of nutrients across the data sets, however, included low, medium, high, and very high levels of ratings. The Deviation Square Index was developed and applied for the variability measurement and found that the largest variation was with phosphorus distribution, followed by potassium, nitrogen, and organic matter. The coefficient of variation (CV%) analysis also exhibited similar trends in nutrient distributions. Nitrogen was the main determinant explaining the variations in rice yield, while phosphorus and potash were negatively related to the yield. An index of fertilizer nutrient recommendation called Test-Value Specific Dose (TVSD) was developed and used to calculate the nutrient recommendation for each sampled location. This new method gave easy and more accurate doses of fertilizer over the blanket recommendation to fit the variations across the soil samples.</p>

Characterisation and Mapping of Soils in Major Coffee Growing Regions of Uganda

There is limited information on the soil nutrient status, site specific fertilizer and agronomic recommendations for coffee in Uganda hence limiting its production and productivity. Therefore, this study was undertaken to characterize the soils under coffee farms and provide fertilizer and land management recommendations for coffee farming in selected districts in Uganda. 717 soil samples were collected from 45 coffee growing districts that were purposively selected to represent the major coffee growing regions of Eastern, Northern, Western, Mid-west and West Nile. 35 districts were sampled from Robusta coffee growing areas and 10 districts from Arabica coffee growing areas. Parameters considered in the laboratory analysis included; pH, total organic carbon, total nitrogen, available P, exchangeable Calcium (Ca), Sodium (Na), Magnesium (Mg), and Potassium (K) and micro elements: Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn) and Boron, soil texture, bulk density and hydraulic conductivity. Soil nutrient levels distribution maps for Robusta and Arabica coffee growing regions were generated in ArcGIS for the entire country. The soil chemical and physical properties were subjected to analysis of variance using Genstat 14th edition. The soil mapping results showed that, the overall average soil macro-nutrients concentrations were significantly different across regions (p < 0.05) with Eastern having the highest levels of macro elements (CEC of 19.28 meq/100 g, Base Saturation (BS) of 43.40%, pH of 5.78, N of 0.20%, K of 1.64 meq/100 g, P of 107.68 mg/kg and OM of 3.31%) followed by Western region. No significant difference (p > 0.05) was recorded for the micronutrients across the different regions, except Zn (p < 0.05). This study showed that Phosphorus and Potassium were generally moderate to high levels in most of the regions sampled while Nitrogen and organic matter were moderate to low. Results from this study provide a general picture of the nutrient status across all coffee growing regions in Uganda and highlight the required modifications for increased production and productivity.

Yield Response of Hybrid and Open Pollinated Maize (Zea mays L.) Varieties to Different Levels of Fertilizer Nitrogen under Rain-Fed Conditions in the Bono Region of Ghana

Background. The experiment was undertaken at Nsapor, a suburb of Berekum municipality in the Bono Region of Ghana, from March 2019 to November 2019 to determine the suitable rate of fertilizer nitrogen application to optimize seed yield and yield attributes of Pannar 12 and Omankwa maize varieties in a semi deciduous agroecology of Ghana. Soil fertility is low in Ghana because of factors such as rampant annual bushfires, short fallow periods as a result of high human populations, continuous cropping, deforestation, and improper mining activities. There is also little information on crop variety and site-specific fertilizer recommendations in Ghana, resulting in inappropriate use of fertilizers by most Ghanaian farmers, culminating in low crop yields. Methods. Hybrid (Pannar 12) and open pollinated (Omankwa) maize varieties were treated with four rates of fertilizer nitrogen obtained from NPK 15-15-15 (0 kgN/ha, 90 kgN/ha, 120 kgN/ha and 150 kgN/ha) and laid out in a factorial combination in a randomized complete block design with three replicates. Results. Application of 150 kg/ha of fertilizer N to Pannar 12 variety resulted in grain yields of 6146 kg/ha and 6095 kg/ha in the major and minor rainy seasons, respectively. The results also showed that application of 120 kg/ha of fertilizer N to Omankwa variety gave grain yields of 4635 kg/ha and 5286 kg/ha in the major and minor rainy seasons, respectively. To optimize the grain yield of maize, farmers could use NPK 15-15-15 fertilizer as a source of nitrogen and apply 120 kgN/ha to Omankwa variety and 150 kgN/ha to Pannar 12 variety in both major and minor rainy seasons.

An integrative approach based on crop modeling and geospatial and statistical analysis to quantify and explain the maize (Zea mays) yield gap in Ghana

In Ghana, maize (Zea mays) is a crop crucial to achieving food and nutrition security. Maize consumption has increased exponentially over the past decades and contributes to 25% of the caloric consumption in the country. In order to assist in decision-making and guide investment in sustainable intensification of maize production, this study set out to identify the determinants of yield and to arrive at potential interventions for closing the maize yield gap. These were quantified using analytical approaches that combine a light use efficiency crop model (LINTUL-1) with statistical and geospatial analyses. Legacy data, auxiliary covariables, and maize fertilizer trials on eight experimental stations in Ghana were used in this study. Overall, the maize yield gap across the stations and trial treatments ranged from 17% to 98%. The variation in yield gap within a single station indicates a significant scope for closing the yield gap through site-specific nutrient management. Multiple linear regression models that explained 81% of the variability in maize yield gap identified soil organic matter, soil water-holding capacity, root zone depth, rainfall, sulfur fertilizer, and nitrogen fertilizer, in that order of importance, as the major determinants for closing the yield gap in the major agroecological zones of Ghana. The yield gap decreased by 1.4 t ha-1 with a 1% increase in soil organic matter. A 1 mm increase of the soil water-holding capacity reduced the yield gap by 1.06 t ha-1, while an increase in pH and in the application of potassium fertilizer widened the gap. These results suggest that both soil physical and chemical properties, together with weather data, should be taken into consideration to arrive at site-specific fertilizer recommendation and other agronomic practices.

Site-Specific Fertilizer Recommendation for Barley (Hordeum vulgare L.) Using the QUEFTS Model in Wolaita Zone in Southern Ethiopia

Although Ethiopia is a center of barley domestication and diversity, and barley has an important place in African dry land agriculture due to its resilience to wide-ranging stresses; the average yield continues to be low, mainly due to low soil fertility. Site-specific fertilizer recommendation for barley in Wolaita, Ethiopia, has a pivotal role not only in optimizing barley productivity but also in maintaining ecological balance. Thus, this study was conducted to assess the relationship between grain yield and site-specific nutrient requirements for a target yield using a Quantitative Evaluation of the Fertility of Tropical Soil (QUEFTS) model. The data input was derived from field experiments predominantly in the major barley production areas of Wolaita, Ethiopia. Calibration of the QUEFTS model was estimated by describing the two boundary lines of the maximum accumulation and dilution of N, P, and K contents targeting the barley grain yield. The study revealed that balanced nutrient requirements estimated by the QUEFTS model had a good correlation between the simulated and observed grain yields (r2 = 0.82 ∗ , 0.88 ∗ , and 0.83 ∗ ) for different sites, namely, Doga Mashido, Kokate, and Gurimo Koyisha, respectively, while evaluation of the QUEFTS model by U-Theil values showed a good agreement between the simulated and observed yields. Therefore, the study concluded that the QUEFTS model can be used for determining nutrient requirements of crops, thereby contributing to the development of site-specific fertilizer recommendations.

Spatial approach for diagnosis of yield-limiting nutrients in smallholder agroecosystem landscape using population-based farm survey data.

Adept use of fertilizers is critical if sustainable development goal two of zero hunger and agroecosystem resilience are to be achieved for African smallholder agroecosystems. These heterogeneous systems are characterized by poor soil health mainly attributed to soil nutrient depletion. However, conventional methods do not take into account spatial patterns across geographies within agroecosystems, which poses great challenges for targeted interventions of nutrient management. This study aimed to develop a novel population-based farm survey approach for diagnosing soil nutrient deficiencies. The approach embraces principles of land health surveillance of problem definition and rigorous sampling scheme. The advent of rapid soil testing techniques, like infrared spectroscopy, offers opportune avenues for high-density soil and plant characterization. A farm survey was conducted on 64 maize fields, to collect data on soil and plant tissue nutrient concentration and grain yield (GY) for maize crops, using hierarchical and purposive sampling. Correlations between soil test values with GY and biomass were established. The relationship between GY, soil NPK, and the tissue nutrient concentrations was evaluated to guide the setting up of localized critical soil test values. Diagnosis Recommendation Integrated System (DRIS) indices for total nitrogen (N), total phosphorus (P), and total potassium (K) were used to rank and map the prevalence of nutrient limitations. A positive correlation existed between plant tissue nutrient concentration with GY with R2 values of 0.089, 0.033, and 0.001 for NPK, respectively. Soil test cut-off values were 0.01%, 12 mg kg-1, 4.5 cmolc kg-1 for NPK, respectively, which varied slightly from established soil critical values for soil nutrient diagnostics. N and K were the most limiting nutrients for maize production in 67% of sampled fields. The study demonstrates that a population-based farm survey of crop fields can be a useful tool in nutrient diagnostics and setting priorities for site-specific fertilizer recommendations. A larger-scale application of the approach is warranted.

Estimating Nutrient Uptake Requirements for Melon Based on the QUEFTS Model

Imbalanced and excessive fertilizer application has resulted in low yields and reduced nutrient use efficiency for melon production in China. Estimating nutrient requirements is crucial for effectively developing site-specific fertilizer recommendations for increasing yield and profit while reducing negative environmental impacts. Relationships between the yield and nutrient uptake requirements of above-ground dry matter were assessed using 1127 on-farm observations (2000–2020) from melon production regions of China. The quantitative evaluation of fertility of tropical soils (QUEFTS) model was used to estimate nutrient requirements. It predicted a linear increase in yield at balanced nutrient uptake levels until the yield reached approximately 60–80% of the potential yield. In order to produce 1000 kg of fruit, 2.9, 0.4 and 3.2 kg/ha of N, P and K (7.2:1.0:7.8), respectively, were required for above-ground parts, while the corresponding nutrient internal efficiencies were 345.3, 2612.6 and 310.0 kg per kg N, P and K, respectively, whereas 1.4, 0.2 and 1.9 kg of N, P and K were required to replace nutrients removed after harvest. The corresponding fruit absorption rates were 47.0%, 59.5% and 58.2%, respectively. Field validation experiments confirmed the consistency between observed and simulated uptake rates, indicating that this model could estimate nutrient requirements. These findings will help develop fertilizer recommendations for improving melon yield and nutrient use efficiency.

Response of Bread Wheat (Triticum aestivum L.) Varieties to Blended Fertilizer Rates on Quality Attributes and Economic Advantages

Bread wheat (Triticum aestivum L.) quality is an important component of the crop productivity as it improves both food security and income sources for farmers. However, its grain quality and economic yields are mainly constrained by poor soil fertility and lack of site specific fertilizer recommendation in the study area for specific variety. Therefore, a field experiment was conducted in Tiyo district of Arsi Zone, Ethiopia, on farmer's field in 2018 main cropping season in response of bread wheat varieties to blended fertilizer rates on quality attributes and its economic advantages. Factorial combination of two improved bread wheat varieties (Wane and Kingbird) and seven fertilizer treatments [Control, Recommended NP (150 kg ha-1 TSP (69%P2O5 ) + 158.7 kg ha-1 Urea (73 N)), 100 kg NPSB + recommended urea (46 kg N) , 150 kg NPSB + recommended urea, 200 kg NPSB + recommended urea, 250 kg NPSB + recommended urea, 300 kg NPSB + recommended urea.] were laid out in randomized complete block design with three replications. Results revealed that grain protein content and hectoliter weight were significantly affected by the main effect of varieties and fertilizer rates with highest grain quality obtained from Wane variety at 200 kg NPSB + 100 kg Urea ha-1 , and recommended NP fertilizer application. The partial budget analysis results revealed that the application of 200 kg NPSB ha1 + 100 kg Urea ha-1 on Wane and Kingbird varieties gave maximum marginal rates of return of 992.8% and 546.3% with highest net benefits respectively. Therefore, application of NPSB at the rate of 200 kg NPSB ha-1 + 100 kg Urea ha-1 in the production of Wane and Kingbird varieties produced better bread wheat quality and economic advantages for the experimental area of wheat production.

A data-mining approach for developing site-specific fertilizer response functions across the wheat-growing environments in Ethiopia

Summary The use of chemical fertilizers is among the main innovations brought by the 1960s Green Revolution. In Ethiopia, fertilizer application during the last four decades has led to significant yield gains, yet yield remains below its potential across much of the country. One of the main challenges responsible for low yield response to fertilizer application has been the use of ‘blanket’ recommendations, whereby no tailoring of fertilizer amount and frequency is done based on soil requirements. As a result, the amount of fertilizer applied ranges widely, and can be either sub- or supra-optimal. There is thus an increasing need for site-specific fertilizer recommendations which take into account site characteristics such as climate variables (temperature, rainfall, and solar radiation); soil factors (soil organic carbon, moisture, pH, texture, cation exchange capacity, and level of macro- and micronutrients); and topographic position indices. This article reports on a data-mining approach we developed on a large dataset of 6585 wheat (Triticum aestivum) field trials. The dataset includes detailed, site-specific biophysical variables to create nutrient response functions that can guide optimal site-specific fertilizer application. The approach used a machine-learning model (random forest) to capture the relationship between nutrients – nitrogen (N), phosphorous (P), potassium (K), and sulfur (S) – and wheat yield. The model explained about 83, 82, 47, and 69% of variances of yield for N, P, K, and S omission, respectively, with consistent performance across training and testing datasets. Expectedly, for N and P omission data, the most important explanatory variables are nutrient rate, followed by soil organic carbon and soil pH. For K and S, however, climatic variables played an important role alongside nutrient rates. The site-specific yield–fertilizer response curves derived from our model are highly variable from location to location, as they are affected by the climatic, soil, or topographic conditions of the site. Importantly, using principal component analysis, we showed that the shape of the fertilizer response curves is a result of the multiple environmental factors (including soil, topography, and climate) that are at play at a given site, rather than of a specific dominant one. The research output is expected to respond to the national policy demands for a sound method to identify the optimal fertilizer rate to increase economic returns of fertilizer investments and take fertilizer utilization research one step further.

Chemical Fertilizer Imports and the Environment: Evidence-based Approach for a Green Economy Accounting for the Tradeoff

The direct and indirect impact of high-input use agriculture- popularised by the Green Revolution- on the environment is the major thrust of this perspective. The paper discusses an integrated approach to minimise the negative impacts, accounting for the proposed ban of synthetic fertilizers and the tradeoff between the environment and productivity resulting from such a ban. Noteworthy stylised facts of the discussion are threefold. First, the Green Revolution reduced the growth of extensive expansion of agricultural lands via intensification, which subdued the pressure on forest cover. Additionally, productivity increase releases marginal lands for vital ecological services such as pollinator habitats. Second, synthetic fertilizer resulted in higher productivity in the agriculture sector, increasing the GDP and facilitating structural transformation. Given that a quarter of the workforce is in the agriculture sector, gradual movement of the labor force to the industrial sector is vital, while the agriculture sector workforce become self-reliant in facing environmental and climatic events. Thus, continuous investment in agricultural productivity growth should be a priority to create fiscal space for the investments in meaningful green initiatives and reduce the vulnerability of the rural poor. Third, evidence-based solutions such as site-specific fertilizer recommendations, soil testing, and discouraging overuse of nitrogenous fertilizer through tariffs should be practised to mitigate the adverse environmental impact of synthetic fertilizer, especially nitrogen fertilizer. Complete removal of the subsidy may generate overreaching welfare and environmental ramifications, although it is widely suggested.

Spatial prediction of soil acidity and nutrients for site-specific soil management in Bedele district, Southwestern Ethiopia

BackgroundUnderstanding the spatial variability of soil properties is useful to tailor site-specific agricultural inputs to enhance crop production on a sustainable basis. This study was aimed to assess and map the spatial patterns of soil acidity and nutrients using geostatistical methods and support site-specific lime and fertilizer recommendations in Bedele district, Southwestern Ethiopia.MethodsSoil samples were collected from agricultural land at a depth of 20 cm using grid sampling technique. The semivariogram analysis was performed for accurate spatial prediction and the kriging technique was used for interpolation of soil parameters.ResultsSoil pH varied between 4.5 and 6.8. Soil organic carbon (OC) content ranged from 0.3 to 5.6% and the mean soil OC density was 0.81 kg m−2. Available phosphorus (AvP) ranged from 0.8 to 38.6 mg kg−1 and nearly 80.23% of the soils exhibited very low to low AvP that could be due to fixation by strong acidity. Soils of the study area exhibited very high exchangeable potassium (K), but very low exchangeable calcium (Ca) and magnesium (Mg). The potassium to magnesium ratio (K:Mg) ranged from 0.2:1 to 10.9:1, while the values of calcium to magnesium ratio (Ca:Mg) varied between 0.3 and 3.4. Among the soil parameters, exchangeable Ca (CV = 54%) and K:Mg ratio (CV = 57.62%) were more variable than other soil parameters. Spatial variability was lowest for soil pH (CV = 10%).ConclusionsMajor portions of the study site were affected by strong acidity (pH ≤ 5.5). Accordingly, about 89% of the soils require lime that varied between 0.09 and 3.6 tons ha−1. In addition to soil acidity, deficiency of available P, Ca, and Mg were the major liming factors affecting crop production in the study area. Digital soil mapping was used to show the spatial variability of soil acidity and nutrients across agricultural land and applied for efficient lime and nutrients advisory works.

Effect of Blended NPSZnB Fertiliser Rates on Growth and Yield of Tef [Eragrostis tef (Zucc.) Trotter] Varieties in Haro Limmu District

Tef (Eragrostis tef (Zucc.) Trotter] is one of the most important cereal crops and predominant staple food in Ethiopia. However, its productivity is constrained by a number of problems, lack of site-specific fertilizer recommendation and high yielding varieties are crucial in the study area. Hence, a field experiment was conducted during 2020 main cropping season to identify most productive variety and determine most economically feasible blended NPSZnB fertilizer rate at Farmers Training Center in Ucha Kebele, Haro Limmu district. The experiment included five different NPSZnB fertilizer rates (0, 50,100, 150 and 200 kg ha-1) and three Tef varieties (Negus, Tesfa and local). The treatments were factorially combined and laid out in randomized complete block design with three replications. Days to 50% heading, days to 90% physiological maturity, plant height and thousand seed weight of Tef were significantly influenced by main effect of varieties, blended NPSZnB fertilizer rates and their interactions. Panicle length, dry biomass yield, lodging index, grain yield, straw yield and harvest index of Tef were significantly (P<0.001) affected by main effect of blended NPSZnB fertilizer rates and the interactions of the two factors, while the panicle length, dry biomass yield, lodging index and grain yield, straw yield and harvest index of Tef were significantly (P<0.01; 0.05) affected by main effect of varieties respectively. Highest (118.20 cm) plant height, dry biomass yield (9. 64 t ha-1), straw yield (7.02 t ha-1), grain yield (2.62 t ha-1), thousand seed weight (0.42 t ha-1) and harvest index (27.1%) were recorded from Tesfa variety with 150 kg NPSZnB ha-1 blended fertilizer rate. Similarly, the highest (7.42 t ha-1), straw yield, dry biomass yield (9.76 t ha-1), grain yield (2.34 t ha-1), thousand seed weight (0.4 g) and panicle length (44.20 cm) were recorded from Tesfa variety with application of 200 kg NPSZnB ha-1 blended fertilizer rate and the highest total number of tillers (10.1) and effective number of tillers (9.7) were recorded with 150 kg NPSZnB ha-1 blended fertilizer rate. Grain yield of Tef showed increment by 91.22 % with the application of 150 kg NPSZnB ha-1 with Tesfa variety over the control. Highest net profit of ETB 83229.4 with marginal rate of return of 1553.71% was recorded from Tesfa variety with application of 150 kg NPSZnB ha-1 blended fertilizer rate. Therefore, farmers of the study area should use Tesfa variety based on the grain yield and net profitability benefits achieved with 150 kg NPSZnB ha-1 fertilizer rate to enhance Tef production and productivity. However, this experiment was conducted only for a single season and site, further study has to be done under different seasons and agro-ecologies to make more reliable recommendations.

Grain Yield and Yield Components Response to Omission of Nutrients on Maize (Zea Mays L.) at Kersa District, Jimma Zone, Ethiopia

The nutrient supply capacity of a soil varies with soil types as well as with farmers’ crop management practices. Yet fertilizer application in Ethiopia is based on regional recommendations, which do not take in to account the variability in soil types as well as farmers’ crop management practices. Thus, site specific fertilizer recommendation that considers soil variability and difference in farmers’ crop management practices is quite important. A field experiment was conducted with an objective to identify which of macronutrients N, P and K are limiting maize grain and yield components in the study area during 2017/18 cropping season. The experiments were laid out in a completely randomized block design with six treatments replicated across six farmers’ fields in Kersa district, Jimma zone, south western Ethiopia. The trial consisted of six treatments, which include the unfertilized control, PK, NK, NP, NPK and NPK+. Maize grain yield was the highest for the NPK treatment followed by NPK+ treatment but lowest for the unfertilized control and N omitted plots. The magnitude of grain yield reduction due to nutrient omission followed the trend of N omission> P omission> K omission. In the absence of N, P, and K maize grain yields were significantly lower compared to that of NPK and NPK+ treatments. From among the different treatments, NPK gave the highest grain yield(9185 kg ha -1 ), while the control treatment gave the lowest grain yield (1861.3 kg ha -1 ).Grain yield levels obtained for different fertilizer treatments were ranked as NPK > NPK+>NP>PK>NK, illustrating that N deficiency was the most yield limiting nutrient followed by P and K in that order. Therefore, the use of appropriate balanced fertilizers should be used for efficient nutrient uptake which ultimately increases maize productivity. Keywords: Maize, Nitrogen, Nutrient omission, Phosphorus, Potassium DOI: 10.7176/JEES/11-8-04 Publication date: August 31 st 2021

Establishment and validation of site specific fertilizer recommendation for increased barley (Hordeum spp.) yield, northern Ethiopia

Establishing model based balanced nutrient requirements for barley (Hordeum spp.) in the northern Ethiopia can solve the fertilizer recommendation problems and enhance crop yield. The Quantitative Evaluation of Fertility of Tropical Soils (QUEFTS) model was used to estimate balanced nitrogen (N), phosphorus (P) and potassium (K) requirements for barley production in Alaje, northern Ethiopia. The objectives were to (i) quantify soil N, P and K supply and recommend fertilizers using QUEFTS model; (ii) investigate response of QUEFTS fertilizer application on yield and nutrient uptake and (iii) validate QUEFTS model performance. The experiment had four treatments: (T1) model based fertilization; (T2) blended fertilization; (T3) farmers’ fertilization practices and (T4) control/no fertilizer. Soil information of the experimental plots were analyzed and used as model input to estimate soil nutrient supplies and recommend fertilizer. Yield and agronomic data were recorded and nutrient uptake and use efficiencies were analyzed. Model performance and accuracy were also checked using root mean square error, coefficient of determination, index of agreement and percent bias. The result revealed that the N, P and K soil supply ratio in the field experimental plots were 9:1:6. The higher grain yield of 4747 kg ha−1 was recorded in the QUEFTS based fertilization plots. Validation results indicated that there is a good correlation between the QUEFTS predicted and observed grain yields implying that the QUEFTS model can be a base for development of simple and cost-effective decision support tools for nutrient management and fertilizer recommendations. Thus, the model performance and prediction accuracy is promising and can help farmers to adjust fertilizer application rates based on crop requirements.

Cultivation of Cowpea Challenges in West Africa for Food Security: Analysis of Factors Driving Yield Gap in Benin

Feeding the world in 2050 requires us to find ways to boost yields of the main local crops. Among those crops, cowpea is one of the grain legumes that is playing an important role in the livelihood of millions of people in West Africa, especially in Benin. Unfortunately, cowpea on-farm yields are very low. In order to understand the main factors explaining cowpea yield gaps, we collected and analyzed detailed survey data from 298 cowpea fields in Benin during the 2017, 2018 and 2019′s rainy seasons, respectively. Composite soil samples were collected from cowpea fields and analyzed in the laboratory. Data on farm field management practices and field conditions were recorded through interviews with 606 farmers. Average cowpea grain yields were low and seldom surpassed 700 kg ha−1 on farmer’s fields. Significant differences were observed between cowpea grain yields from northern to southern Benin (p < 0.05), and the lowest yields were observed in northern Benin. These low yields are related to crop management practices, soil nutrient contents, and the interaction of both. According to the model of regression tree from northern to southern Benin, the use of mineral fertilizer, insecticide sprays to control pests, and the improvement of phosphorus, nitrogen, potassium (P, N, K) and cation sum content in the topsoil would increase cowpea grain yields. Insect pests, diseases, and soil fertility decline are the largest constraints limiting grain yield in Benin. Future research should focus on formulating site-specific fertilizer recommendations for effective cowpea cultivation in Benin, as well as the control of insect pests and diseases.

Variability in yield responses, physiological use efficiencies and recovery fractions of fertilizer use in maize in Ethiopia

Physiological use efficiency (PUE), recovery fraction of applied nutrients and indigenous soil nutrient supply form the basis of site-specific fertilizer recommendations. To derive these parameters, and understand their variability, as well as yield responses and fertilizer use profitability, nutrient omission trials (NOTs) were conducted in farmers’ fields across different agro-ecologies in Bako (n = 37), Central Rift Valley (CRV) (n = 66) and Jimma (n = 44) regions of Ethiopia in the main crop growing seasons of 2015 and 2016. The treatments used in the NOTs were control, PK, NK, NP, NPK and NPKSM, where SM refers to secondary and micro nutrients, and applied levels of N, P and K, were 120, 40 and 40 kg /ha, respectively. The results showed that the average yields of the control treatment were 4.5, 3.1 and 2.9 t/ha in Bako, CRV and Jimma, whereas the average yields for the NPK treatment were 8.3, 4.9 and 7.9 t/ha in the respective regions. Nitrogen was limiting grain yield in all the three regions, whereas P limited yield only in CRV and Jimma. The average N agronomic efficiencies in Bako, CRV and Jimma were 25.7, 13.3 and 35.5 kg grain kg−1 of applied N, respectively, under NPK fertilizer use. With the levels of fertilizer used in the NOTs, NK, NP and NPK treatments were profitable in Bako and Jimma, whereas PK was not. None of the fertilizer treatments were profitable in CRV. Soils in Bako and Jimma supplied more N and K but less P than the soils in CRV. The PUE at maximum accumulation, median and maximum dilution of N were 27, 54 and 80 kg grain kg-1 N, while for P, the values were estimated to be 194, 350 and 505 kg grain kg-1 P, and for K they were 16, 52 and 87 kg grain kg−1 K. The estimated average N, P and K recovery fractions were 0.29, 0.05 and 0.06, respectively, in Bako, 0.22, 0.10 and 0.15 in CRV, and 0.38, 0.10 and 0.01 in Jimma. While these average parameter values are relevant, in particular agronomic use efficiencies and recovery fractions showed large variability and, moreover, averages were lower than what is deemed feasible with good agronomy. We discuss the variability in the derived parameters, the relation with yield levels, soil nutrient supply and rainfall, and conclude that caution is needed when deriving fertilizer recommendations from parameters obtained in on-farm experiments. Using single estimated average values is not sufficient: variability in these parameters and sub-optimum values need to be explained first, and derived insight should be used when developing site-specific fertilizer recommendations.

Soil-based, field-specific fertilizer recommendations are a pipe-dream

Fertilizer recommendations are key for farmers: the investment is relatively large for smallholders and risky with unknown yield responses and variable fertilizer prices. Are agronomists able to provide useful site-specific fertilizer recommendations that reduce these uncertainties? We evaluated the influence of errors introduced due to soil sampling and chemical analysis procedures both within- and among laboratories on fertilizer recommendations. Using what we consider to be conservative estimates of the uncertainty in estimating soil supply of N, P and K in a single composite soil sample, the resulting 90% confidence interval of fertilizer recommendations ranged from 86 to 186, 0–58 and 38–114 kg N, P and K ha−1 respectively. The numerous laboratory services and digital applications providing field-specific recommendations appear to promise more accuracy than soil analysis can realistically deliver. We conclude that a field-specific fertilizer recommendation based on a single composite soil sample is indeed a pipe-dream.

Development and utilization of a decision support tool for the optimization of fertilizer application in smallholder farms in Uganda

This paper presents the development and pilot of the Fertilizer Optimization Tool (FOT), a decision support tool for use by extension agents in advising smallholder farmers in Uganda in applying optimum (rather than maximum) fertilizer by considering the farmers’ financial abilities. The FOT is made up of three components which includes, the optimizer tool, the nutrient substitution table, and a fertilizer calibration tool. The FOT was developed using field trial data collected on specific agro-ecological zones and mapped using global positioning systems in 13 Sub-Saharan Africa countries. The FOT provides site- and farmer-specific fertilizer recommendations, providing both economic and environmental benefits. Results are based on a survey of 241 households, 57 technical personnel and tracking of 33 FOT users over a 3-season period. Results show a progressive shift in farmers’ attitude towards the value of fertilizer. More FOT users (71%) disagreed with the statement that fertilizers destroy soils, compared with non-FOT users (52%). Crop yields (tons/ha) were significantly higher for crops receiving fertilizers compared to those not. While it is generally accepted that using fertilizer improves crop response and achieves better yields, the value of FOT was reported in terms of rationalization of investment by farmers. The average seasonal investment was approx. $43, giving a return on investment of over 107%. Given the evidence generated from Uganda, there is a need for considering out scaling the FOT technology to other countries in Africa, which are faced with the same challenges of low fertilizer use among smallholder farmers. Using the mobile FOT app provides a further cost-effective opportunity to out scale the approach to benefit more smallholder farmers in sub-Saharan Africa. Further development of the FOT is suggested, particularly in the wake of increased focus on multi-nutrient fertilizer blends, and the need to adjust for soil PH, moisture, and long-term impacts of nutrient substitution. Key words: decision support tool, fertilizer optimization tool, precision agriculture, site-specific fertilizer recommendations

Effect of Nitrogen Fertilizer Levels and Row Spacing on Yield and Yield Components of Upland Rice Varieties in Pawe, Northwestern Ethiopia

Rice (Oryza species) is a major cereal crop in Pawe area. However the yield of the crop is low due to lack of site specific row spacing and fertilizer recommendation. Hence, a field experiment was conducted in Pawe Agricultural Research center during the rainy season of 2016 to assess the effect of row spacing and nitrogen fertilizer level on grain yield and yield component and to determine their economic feasibility on up-land rice varieties under rain-fed conditions. Two varieties (NERICA-4 and Pawe-1), three row spacing (RS) (20, 25 and 30 cm) and four N levels (0, 32, 64 and 96 kg ha -1 ) were laid out in Randomized Complete Block Design in factorial combination with three replications. Among the main treatment, variety NERICA-4 showed significantly taller plant height and panicle length. Interaction effect of variety, RS and N levels highly significantly (P < 0.01) affected the number of total tiller m -2 (NTT), fertile tiller 0.5 m -2 row length (FT), thousand kernels weight (TKW), above ground dry biomass yield, straw yield (STY) and harvest index, and significantly (P<0.05) affected grain yield (GY) ha -1 . The highest (420.0 m -2 ) NTT was found by variety NERICA-4 at 20 cm RS and 96 kg N ha -1 . The highest GY (6462.56 kg ha -1 ) was obtained by variety NERICA-4 at RS 20cm and 96 kg N ha -1 and the lowest GY (1935.5 kg ha -1 ) was obtained by variety Pawe-1 at RS 30 cm and no N input. The highest STY (8477.2 kg ha -1 ) was produced by variety Pawe-1 at 20 cm RS and 96 kg N ha -1 . The attractive net benefit (32,063.8 birr ha -1 ) with acceptable marginal rate of return (453.4%) for farmers in Pawe was found from variety NERICA-4 interacts with RS 20 cm and 96 kg N ha -1 . Keywords : - Biomass Yield, Grain Yield, Interaction effect, NERICA-4, Net benefit. DOI: 10.7176/JNSR/10-11-01 Publication date: June 30th 2020

A Site-Specific Fertilizer Recommendation Based on the Phosphorus and Potassium Status in Mempawah District, West Kalimantan

The recommendations of Phosphorus (P) and Potassium (K) fertilization for rice are still not site-specific yet due to a lack of required soil data information. The P and K status of the paddy fields that provide information on the low, medium, and high P and K nutrient status are very useful for determining recommended the site-specific fertilizer in the the district area. The purpose of the research was to determine the site-specific fertilizer recommendation for paddy field based on their P and K status. This research was based on the field survey and the soil analysis in the laboratory. The soil samples were taken using a grid system, and the P and K levels were assessed by using a 25% HCl extraction. Soil samples were taken in a composite manner on all paddy fields in which their status have been identified. The composite soil samples were determined from 10 - 15 individual samples (sub-samples) with a sampling distance of each sub-sample of 25-50 m in the field. The soil samples were taken in the overlay with a depth of 0-20 cm. Taking sub-samples were done by a diagonal or a zigzag method according to the conditions of paddy fields. The results of the study presented that the nutrient status of P and K and the fertilizer recommendations in paddy fields for rice plants located in 9 sub-districts in Mempawah Dsitrict had shown that nutrient status of P, on average, were from moderate to high levels, meanwhile, the nutrient status of K was from low to high levels. Recommendations for fertilizing rice fields in several sub-districts in Mempawah Regency are mostly 150 kg NPK (15:15:15) ha-1, 200 kg Urea ha-1 and 25 kg KCl ha-1.