Sludge as an initial nutrient driver for yield improvement in the poor soils of northern Namibia

The northern part of Namibia suffers from drought and low-quality soil. The soil needs a boost of nutrients, and the water must be used in a frugal manner. Thereby, the objective of this research was to investigate the effect of sludge and treated wastewater as initial nutrient drivers in sandy loam soil by examining the dry biomass (DM), the nutrient uptake, and the heavy metal accumulation in the organs of sorghum. For this reason, sludge, chemical fertiliser, and a mixture of both were applied to a sorghum field. As a second factor, water of two different qualities was used: (a) treated wastewater (TWW), and (b) tap water. The treatment with mixed-fertiliser produced 16% more DM compared to the treatment with chemical fertiliser when irrigated with tap water. The use of TWW enhanced phosphorus uptake in the treatment with chemical fertiliser but did not increase the DM. This study suggests that sludge can be applied as an initial nutrient driver for poor soil with low organic matter and that TWW can also be an important complementary water resource for irrigation in areas affected by drought.