Sub-Saharan African smallholder farmers face challenges due to limited access to commercial fertilizers, affecting food security. Exploring the benefits of intercropping is promising, but evaluating crop performance in specific agroecological contexts is crucial. This study in Vilankulo, Mozambique, conducted over two growth seasons (2018 and 2019), aimed to assess the benefits of intercropping maize (Zea mays L.) and cowpea (Vigna unguiculata L., Walp) (M+C) compared to maize (M) and cowpea (C) as sole crops. Key variables for comparison included dry matter yield (DMY), land equivalent ratio (LER), competitive ratio (CR), tissue nutrient concentration, nutrient recovery, and apparent N fixation (ANF). This study also examined the effects on cabbage (Brassica oleracea L.), cultivated as a succeeding crop, and soil properties. In 2018, maize plants were severely affected by drought and did not produce grain. This year, cowpea grain yields were 2.26 and 1.35 t ha⁻¹ when grown as sole crop or intercropped. In 2019, maize grain yield was 6.75 t ha⁻¹ when intercropped, compared to 5.52 t ha⁻¹ as a sole crop. Cowpea grain yield was lower when intercropped (1.51 vs. 2.25 t ha⁻¹). LER values exceeded 1 (1.91 and 1.53 for grain and straw in 2019), indicating improved performance in intercropping compared to sole crops. In 2019, CR was 1.96 for maize grain and 0.58 for cowpea grain, highlighting the higher competitiveness of maize over cowpea. Cowpea exhibited higher average leaf nitrogen (N) concentration (25.4 and 37.6 g kg⁻¹ in 2018 and 2019, respectively) than maize (13.0 and 23.7 g kg⁻¹), attributed to its leguminous nature with access to atmospheric N, benefiting the growth of maize in intercropping and cabbage cultivated as a succeeding crop. Cowpea also appears to have contributed to enhanced phosphorus (P) absorption, possibly due to access to sparingly soluble P forms. In 2019, ANF in M+C was 102.5 kg ha⁻¹, over 4-fold higher than in C (25.0 g kg⁻¹), suggesting maize accessed more N than could cowpea provide, possibly through association with endophytic diazotrophs commonly found in tropical grasses.

In sub-Saharan Africa, soil fertility management must rely on local fertiliser resources since most smallholder farmers do not have access to industrial fertilisers. In Vilankulo, Mozambique, farmers have access to bat guano and biochar, albeit in small amounts, which makes it even more necessary to manage them correctly to maximise crop productivity. This study was carried out with irrigated maize (Zea mays L.) in a haplic Lixisol during the 2017/2018 and 2019 growing seasons. Nine treatments were established consisting of the application of 5 (G5) and 10 (G10) t ha⁻¹ of guano at sowing, 5 (B5) and 10 (B10) t ha⁻¹ of biochar at sowing, 5 [G5(-1)] and 10 [G10(-1)] t ha⁻¹ of guano one month before sowing, 1 and 4 (B1G4) and 2 and 8 (B2G8) t ha⁻¹ of biochar and guano, respectively, at sowing and an unfertilised control (C). Treatments G10 and B2G8 led to the highest maize yields (3.77 and 2.68 t ha⁻¹ in 2018 and 5.05 and 5.17 t ha⁻¹ in 2019, respectively), and were statistically higher than those of the control (1.35 and 1.63 kg ha⁻¹, respectively). Apparent nitrogen recovery from bat guano was close to 100%, showing almost complete mineralisation during the maize growing season, due to its low carbon/nitrogen ratio and very favourable environmental conditions for mineralisation. Due to the fast release of nutrients, bringing forward the application of the organic amendment before sowing is not recommended, since it reduces nutrient use efficiency. Biochar did not significantly influence maize grain yield or contribute significantly to plant nutrition. To take advantage of its potential effect on some soil properties, its use in combination with other materials of greater fertilising value is recommended.

The difficulty in obtaining commercial fertilizers by smallholder farmers in sub-Saharan Africa makes it very important to optimize the use of local organic resources. In VilanKulo, Mozambique, a study was carried out on okra (Abelmoschus esculentus) over two growing seasons. The soil was a haplic, loamy-sand textured Lixisol. As organic amendments, bat guano and biochar were used. Bat guano is a phosphorus (P)-rich and low-carbon (C)/nitrogen (N)-ratio material from natural deposits on a cave floor. Biochar is a C-rich material prepared via an artisanal process using forest residues as a feedstock. Bat guano was applied at two rates (5 and 10 t ha⁻¹) just before sowing. It was also applied at the same rates one month before sowing. Biochar was used at two rates (5 and 10 t ha⁻¹) applied at sowing. Biochar and guano were mixed at the rates of 1 and 4 t ha⁻¹ and 2 and 8 t ha⁻¹, respectively, and applied at sowing. The experiment also used a non-fertilized control. Field trials were arranged in a completely randomized design with three replicates. The treatments that received high rates of guano tended to show significantly higher fruit yields (>10 t ha⁻¹ as the two-year average) in comparison with the control, which showed the lowest average okra fruit yield (6.21 t ha⁻¹). In the guano treatments, the apparent recovery by okra of some important nutrients, such as N, was greater than the amount of the nutrient contained in the guano itself. This result, together with many others related to the tissue nutrient concentration, soil properties and residual fertilizing value in guano plots, indicated a strong mineralization of guano during the growing season. This was probably due to its low C/N ratio and favourable environmental conditions for the mineralization process. The result also suggests some kind of manuring effect, i.e., a fertilizing effect of guano beyond what can be explained by the nutrient supply. The use of biochar increased the total organic C in the soil and cation exchange capacity (CEC) compared with the control but did not affect the variables related to plant performance. Overall, the results showed that farmers can benefit from the use of guano in the short term because it releases nutrients, while with the use of biochar, the benefits can arise in the long term by improving the soil properties.

Purpose: This study aims to evaluate the potential of sewage sludge as a sustainable alternative to traditional farmyard manures, considering the limited availability of such resources in many regions specializing in crop production. Methods: This study compared the application of sewage sludge (SS) and cow manure (CM) at equivalent nitrogen (N) rates in silage maize ( Zea mays L.) cultivation over two growing seasons. Organic amendments were applied at rates of 50 (SS50, CM50), 100 (SS100, CM100), and 200 (SS200, CM200) kg ha⁻¹ of N, alongside an unfertilized control (N0), with three replicates per treatment in a completely randomized design. Results: Dry matter yield (DMY) increased significantly with the applied dose but showed no significant differences between amendments. N availability indices, including the pre-side-dress soil nitrate test, leaf N concentration, and stalk nitrate test, revealed higher N availability from sewage sludge compared to cow manure at equivalent application rates. Apparent N recovery (ANR) by the end of the second growing season was 99.8%, 90.8%, and 74.5% for SS50, SS100, and SS200, respectively, and 76.7%, 75.4%, and 50.5% for CM50, CM100, and CM200, respectively. Conclusions: The rapid mineralization of sewage sludge likely results from its low carbon (C)/N ratio and the absence of lignin and other low-energy organic compounds, which are less metabolically accessible to soil microorganisms. These properties position sewage sludge as an intermediate between conventional organic compost and mineral fertilizers, making it particularly suitable for cropping systems requiring high short-term N availability.