Waste to resource: use of water treatment residual for increased maize productivity and micronutrient content

Abstract

Soil degradation, which is linked to poor nutrient management, remains a major constraint to sustained crop production in smallholder urban agriculture (UA) in sub-Saharan Africa (SSA). While organic nutrient resources are often used in UA to complement mineral fertilizers in soil fertility management, they are usually scarce and of poor quality to provide optimum nutrients for crop uptake. Alternative soil nutrient management options are required. This study, therefore, evaluates the short-term benefits of applying an aluminium-based water treatment residual (Al-WTR), in combination with compost and inorganic P fertilizer, on soil chemical properties, and maize (Zea mays L.) productivity and nutrient uptake. An eight-week greenhouse experiment was established with 12 treatments consisting of soil, Al-WTR and compost (with or without P fertilizer). The co-amendment (10% Al-WTR + 10% compost) produced maize shoot biomass of 3.92 ± 0.16 g at 5 weeks after emergence, significantly (p < 0.05) out-yielding the unamended control which yielded 1.33 ± 0.17 g. The addition of P fertilizer to the co-amendment further increased maize shoot yield by about twofold (7.23 ± 0.07 g). The co-amendment (10% Al-WTR + 10% C) with P increased maize uptake of zinc (Zn), copper (Cu) and manganese (Mn), compared with 10% C + P. Overall, the results demonstrate that combining Al-WTR, compost and P fertilizer increases maize productivity and micronutrient uptake in comparison with single amendments of compost and fertilizer. The enhanced micronutrient uptake can potentially improve maize grain quality, and subsequently human nutrition for the urban population of SSA, partly addressing the UN’s Sustainable Development Goal number 3 of improving diets.

Coapplication of water treatment residual and compost for increased phosphorus availability in arable sandy soils

“…Al-WTR (Table 2). In our previous work (Gwandu et al, 2021), the application of 14 kg P ha −1 , which translates to 32 kg P 2 O 5 ha −1 was far below the minimum of 57 and 117 kg P 2 O 5 ha −1 estimated at a pH of 7.5-and 2-mm particle size for the 5% and 10% coamendment, respectively (Table 2). The ability of an organic material to reduce or increase P sorption is dependent upon its type, its P concentration and the amount added (Singh & Jones, 1976).…”

“…This has potential implications for the disposal of Al‐WTR in the environment or its use as a soil applicant. Although research has provided evidence of the soil health benefits of coamending Al‐WTR and compost (Gwandu et al, 2021; Hsu & Hseu, 2011; Kerr et al, 2022; Mahmood‐ul‐Hassan et al, 1993), consideration of Al‐WTR particle size is therefore important to reduce P sorption and increase P availability in coamended soils. Finer particles would suit soil remediation purposes such as in instances where there is excess P or heavy metal contamination in the environment.…”

“…Coapplication of Al‐WTR and P fertilizer has been suggested as a possible route for the alleviation of P limitations in Al‐WTR amended soils (Hyde & Morris, 2004; Mahmood‐ul‐Hassan et al, 1993), but the major challenge is that African smallholder farmers have limited access to P mineral fertilizers. Previous results from a greenhouse experiment with maize ( Zea mays L.) as a test crop showed that the addition of P fertilizer at a constant rate of 14 kg P ha −1 to 10% or 20% Al‐WTR amendment levels was not enough to offset the P sorption associated with Al‐WTR (Gwandu et al, 2021). Gwandu et al (2021) showed that the maize P content was <3 g kg −1 , which is the critical limit for P accumulation in maize plant tissue (Tandon, 1993).…”

“…When Al‐WTR is added to the soil, iron (Fe) and aluminium (Al) oxide mineral surfaces within the WTR potentially form strong bonds with soil organic matter (SOM) (Yan et al., 2016), thus protecting SOM from microbial decomposition (Kögel‐Knabner et al, 2008). The use of Al‐WTR as a coamendment has been associated with increased soil aeration, aggregation and water retention (Hsu & Hseu, 2011; Kerr et al, 2022), and increased crop yield and plant micronutrients such as zinc and copper (Gwandu et al., 2021; Mahmood‐ul‐Hassan et al, 1993). On the other hand, the use of Al‐WTRs in agriculture serves as an important alternative disposal route to landfill (Turner et al, 2019).…”

“…Even though research has demonstrated the usefulness of Al‐WTR as a soil amendment (e.g., Clarke et al, 2019; Gwandu et al, 2021; Kerr et al, 2022), there are still concerns about the interaction of Al‐WTR and soil phosphorus (P) (Lombi et al, 2010; Silveira et al, 2013), one of the most limiting nutrients for crop production in Africa (Rurinda et al, 2020). Increased soil P available for plant uptake enhances plant root development, which boosts their capacity to take up nutrients from the soil, thus improving overall crop productivity (Malhotra et al, 2018).…”