Management of nitrogen and water plays a significant role in increasing crop productivity. A large amount of nitrogen (N) may be lost through leaching if these resources are not well managed. Wetting front detectors (WFDs) and Chameleon soil water sensors were used to adapt water and nitrogen applications with the goal of increasing millet yields, as well as nitrogen and water use efficiency. The trials were laid out as a randomized complete block design with factorial combinations of water and N, and included the following treatments: irrigation to field capacity (fortnightly and weekly), adaptive-water application based on sensor response or rainfed, and N treatments included either fixed nitrogen levels (0, 45, 90 kg N ha⁻¹) or an adaptive-N rate, depending on N content of the soil solution extracted from WFDs. Adaptive management aims to steer water and nitrogen applications towards optimum crop requirements. Treatments that received both high water and nitrogen outperformed other treatments by 11% to 68% in terms of biomass production and 16% to 54% in grain yield, while water use efficiency and irrigation use efficiency values were also higher, ranging from 1.58 to 7.94 kg m⁻³ and 1.43 to 8.30 kg m⁻³. Results suggest that integrated adaptive water and nitrogen management should be considered to reduce high N losses and cost of crop production, without a meaningful yield penalty, relative to high production input management.

Lowland wetlands generally have a high agricultural production potential and can be local hot-spots for biodiversity. Specific seasonal wetland system is largely distributed in north-central Namibia. Seasonal wetlands consist of seasonal river wetlands (locally known as oshanas). However, studies on soil fertility, salinity and sodicity in seasonal river wetlands are still limited in this area. The objective of this study was hence to investigate the soil fertility status of seasonal wetlands and evaluate their potential for agricultural production and consider sustainability of the land use system. Soil samples were collected from 102 different spots of the flood plain within 3 major seasonal rivers, and analyzed for their physico-chemical properties and salinity and sodicity. The findings for average soil organic carbon (1.94 g kg-1) and average clay contents (102.3 g kg-1) of seasonal rivers were drastically lower than the wetland of semi-arid Africa regions (organic carbon, 5.8 g kg-1; clay contents, 340 g kg-1), and organic carbon and clay content significantly (p<0.05) decreased at the lower part of each seasonal river. Most of the seasonal river soil’s’ electrical conductivity of saturated paste extract (ECe) and the sodium adsorption ratio of the saturated paste extract (SAR) were more than 4 dS m-1 and 13, respectively. However, there were large differences in electrical conductivity of saturated paste extract (ECe) and the sodium adsorption ratio of the saturated paste extract (SAR) values among the sampling spots. These findings suggest the high agricultural importance to improve the soil organic matter and clay contents, and land selection to avoid the strongly high saline-sodic soil sites in seasonal river. Key words: Seasonal flooded wetland soil, soil fertility, soil salinity and sodicity, sustainable land use.

Pearl millet is an important crop for food security in Asia and Africa’s arid and semi-arid regions. It is widely grown as a staple cereal grain for human consumption and livestock fodder. Mechanistic crop growth and water balance models are useful to forecast crop production and water use. However, very few studies have been devoted to the development of the model parameters needed for such simulations for pearl millet. The objectives of the study were to determine crop-specific model parameters for each of three pearl millet varieties (landrace, hybrid, and improved), as well as to calibrate and validate the Soil Water Balance (SWB) model for predicting pearl millet production and water use based on weather data. The SWB was chosen because it is widely used in southern Africa; however, the developed parameters should benefit other models as well. The presented crop-specific parameter values were derived from field observations and literature. Varieties with different phenology, maturity dates and tillering habits were grown under well-watered and well-fertilised conditions for calibration purposes. The calibrated model was used to predict biomass production, grain yield and crop water use. The hybrid’s water use efficiency was higher than that of the landrace and improved variety.

Pearl millet is a cereal crop vital for food security in Africa and Asia. It is widely adapted for dual-purpose production, providing grain for human consumption and fodder for livestock, particularly during dry seasons. This study aimed to evaluate three dual-purpose pearl millet genotypes from Namibia and South Africa while exploring prospects for future production practices. Growth analysis is essential for quantitatively assessing crop growth, development, and production. A growth analysis study was conducted by collecting and evaluating weather data, water use efficiency, and crop growth parameters that are valuable for modelling, allowing for observing and quantifying strengths and weaknesses between varieties for food and fodder or as dual-purpose varieties. The analysis focused on water use, plant height, fractional radiation interception, panicle number, tiller number, flowering date, stem diameter, panicle length, dry matter distribution, harvest index, grain yield, and panicle diameter, under well-watered, supplementary irrigation, and rainfed conditions. The landrace achieved a higher yield under well-watered conditions than the hybrid and improved varieties. The hybrid pearl millet produced a greater fodder yield than the improved short variety in well-watered and water-limited treatments. The improved variety suits grain production, whereas the landrace and hybrid are more suitable for dual-purpose production. The landrace performed well in rainfed and irrigated situations across the three seasons. The landrace (Kantana) recorded the highest grain yield (1.01 kg m⁻²), followed by the hybrid (Agrigreen) (0.97 kg m⁻²), while the improved variety (Kangara) had the lowest grain yield (0.74 kg m⁻²).

Poor sandy soils in North-central Namibia have been identified as the major constraint limiting agricultural productivity especially in small–scale farming communities. The soils are inherently low in organic matter content, and are characterized by nutrient deficiencies, limiting crop production and sustainable agricultural development. A two-year field experiment was conducted at the University of Namibia–Ogongo Campus to evaluate the effects of different soil amendments on growth and yield of wheat under local climatic conditions. The study adopted a 2×2×2 Factorial laid out in a Randomized Complete Block Design (RCBD) with eight treatments comprising of biochar and compost rates 0, and 10 t ha–1 and nitrogen fertilizer rates 0, 120 kg N ha–1 (B0C0N0, B10, C10, B10C10, B10N120, C10N120, BC10N120, and N120). The results showed that biochar was highly significant (P < 0.001) on plant height, number of spikes plant–1, spike length, shoot biomass and actual grain yield in both Year 1 and 2. The combined application of biochar and nitrogen (B10N120) showed the highest plant height (55.7 and 53.8 cm) in Year 1and 2. The same treatment in both Year 1and 2 yielded high (3.95 and 4.01 t ha‒1, respectively). The interaction of biochar, compost and nitrogen (B10C10N120) significantly increased shoot biomass (6.22 and 6.37 t ha‒1) in Year 1and 2. Therefore, combined application of biochar with nitrogen (B10N120), can be recommended to enhance resilient wheat production on sandy soils in North-Central Namibia.