The Crop Environment Resource Synthesis (CERES)-Maize model in Decision Support System for Agricultural Technology Transfer (DSSAT) was calibrated and evaluated with experimental data for simulation of response of two intermediate-maturing maize varieties to different sowing dates in the Nigerian savannas. The calibration experiments involved 14 consecutive field trials conducted in the rainy and dry seasons in Bayero University Kano (BUK), Dambatta, and Zaria between 2014–2019. Two sets of field experiments were conducted simultaneously for model evaluation in Iburu in the southern Guinea savanna zone and Zaria in the northern Guinea savanna zone during 2015 and 2016 cropping seasons. The experiments for calibration had two maize (SAMMAZ-15 and SAMMAZ-16) varieties planted under optimum conditions with no water and nutrients stresses. The trials for model evaluation were conducted using the same varieties under four different nitrogen (N) rates (0, 60, 120 and 180 kg N ha−1). A 30-year (1985–2014) term simulation was performed to determine effect of varying sowing dates on yields of two maize varieties (SAMMAZ-15 and SAMMAZ-16) in the Sudan savanna (SS), northern Guinea savanna (NGS), and southern Guinea savanna (SGS) zones. The calibration results showed that the cultivar coefficients of the two maize varieties resulted in simulated growth and development parameters that were in good agreement with observed parameters. Model evaluation showed a good agreement between simulated and observed data for phenology and growth of maize. This demonstrated the potential of the CERES-Maize model to simulate growth and yield of maize in the Nigeria savannas. Results of 30-year sensitivity analysis with 9 different sowing windows showed that in SS, sowing the intermediate maize varieties from early to mid-June produced the highest grain yields. In NGS, the optimum sowing windows were found between late June and late July for the both varieties. In SGS, the optimum sowing window is from early June to late July for SAMMAZ-15 and mid-June to late July for SAMMAZ-16. These planting windows gave the highest long-term average yields for each variety. The variety SAMMAZ-15 was found to be best performing across the three agro-ecologies. Maize performance was generally higher in NGS than in SGS. SS in the Sudan savanna recorded the lowest yield compared with other locations.

Low nutrient use efficiency in maize as a result of imbalanced nutrition has been reported to drastically reduce yield. We implemented a nutrient omission experiment to assess the effect of nutrient application on maize yield and nutritional balance. Maize ear leaves were analyzed for nutrients, to identify nutrient balance status using the Diagnostic and Recommendation Integrated System (DRIS) approach. Results indicated that omission of N or P resulted in highly imbalanced DRIS indices respectively, and significantly lower grain yield. A strong inverse relationship between K ear leaf content with DRIS index suggests that K application negatively increases K imbalance in many situations. Imbalances of Mg, Ca and Cu were more associated with higher yielding treatments. A Which-Won-Where result show that nutrient imbalances in the diagnosis were systematically frequent when N was omitted. All the diagnosed nutrients were imbalanced even under the highest yielding NPKZn treatment; indicating further opportunity for yield increase with more balanced nutrition. Balanced nutrition of maize in the maize belt of Nigeria should target application of varying rates of N, P, K, Mg, S and Zn, depending on the soil conditions. But, because of complexities of nutrient interactions during uptake, it is hardly possible to realize a balanced nutrition. However, differentiating the application of antagonistic nutrients into foliar or soil-based methods is recommended for a more balanced maize nutrition.

Site-specific nutrient management can reduce soil degradation and crop production risks related to undesirable timing, amount, and type of fertilizer application. This study was conducted to understand the spatial variability of soil properties and delineate spatially homogenous nutrient management zones (MZs) in the maize belt region of Nigeria. Soil samples (n = 3387) were collected across the area using multistage and random sampling techniques, and samples were analyzed for pH, soil organic carbon (SOC), macronutrients (N, P, K, S, Ca and Mg), micronutrients (S, B, Zn, Mn and Fe) content, and effective cation exchange capacity (ECEC). Spatial distribution and variability of these parameters were assessed using geostatistics and ordinary kriging, while principal component analysis (PCA) and multivariate K-means cluster analysis were used to delineate nutrient management zones. Results show that spatial variation of macronutrients (total N, available P, and K) was largely influenced by intrinsic factors, while that of S, Ca, ECEC, and most micronutrients was influenced by both intrinsic and extrinsic factors with moderate to high spatial variability. Four distinct management zones, namely, MZ1, MZ2, MZ3, and MZ4, were identified and delineated in the area. MZ1 and MZ4 have the highest contents of most soil fertility indicators. MZ4 has a higher content of available P, Zn, and pH than MZ1. MZ2 and MZ3, which constitute the larger part of the area, have smaller contents of the soil fertility indicators. The delineated MZs offer a more feasible option for developing and implementing site-specific nutrient management in the maize belt region of Nigeria.

HighlightsNew and better fitting QUEFTS’ prediction equations for indigenous soil N, P, and K supply were developed for the Northern Nigerian Savanna.A good correlation was observed between the observed and parameterized QUFETS predicted maize grain yield.The QUEFTS model predicted a balanced N, P, K uptake to linearly increase with grain yield until 50-60% of the potential yield.The QUEFTS model is a suitable tool for site-specific nutrient recommendations in maize in the Northern Nigerian Savanna.

Increasing numbers of HIV-infected adults in Africa need hospital care. It remains unclear what impact this has on health care services or on how hospitals respond. The aim of this study was to describe the effects of a rising case load of adult HIV-related disease by comparing results from a prospective cross-sectional study of acute adult medical admissions to a government hospital in Nairobi conducted in 1992 with results from a previous study done in 1988 and 1989 in the same hospital, using the same study design and protocol. Data on age, gender, number admitted, length of stay, HIV status, clinical AIDS, final diagnosis, case mix, and outcome were compared. In 1992, 374 consecutive patients were admitted in 15 24-hour periods (24.9 patients/period) compared with the 1988 to 1989 study, which enrolled 506 patients in 22 24-hour periods (23.0 patients/period). Patients' age, gender, and length of hospital stay were similar in both studies. In 1992, 39% of patients were HIV-positive compared with 19% in 1988 to 1989 (p < 10(-6)); whereas seropositive admissions rose 123% between the two periods (p < .0001), HIV-negative admissions declined 18% (p < .05). Clinical surveillance for AIDS consistently identified <40% of HIV-positive patients. Irrespective of HIV status, tuberculosis and pneumococcal pneumonia were the leading diagnoses in both surveys. No change was found in the diagnoses recorded for HIV-positive patients, but in HIV-negative patients, reductions were significant in the case mix (p < .00001) and range of diagnoses (p < .001) seen in 1992. Outcome remained unchanged for HIV-positive patients with approximately 35% mortality in both surveys. Outcome significantly worsened, in relative and absolute terms, for HIV-negative patients: in 1992, mortality was 23%, compared with 13.9% in 1988 to 1989 (p < .005), with 3.5 deaths per 24-hour period in 1992 compared with 2.6 deaths per 24-hour period in 1988 to 1989 (p < .05, one-tailed). These data suggest that increasing selection for admission is taking place as demand for care increases because of HIV/AIDS. This process appears to favor HIV-positive patients at the expense of HIV-negative patients who seem to be crowded out and, once admitted, experience higher mortality rates. The true social costs of the HIV epidemic are underestimated by not including the effects on HIV-negative people.