Poor soil fertility caused mainly by low and declining soil organic carbon is one of the major constraints limiting crop productivity in tropical and subtropical regions of South Africa. We evaluated the effect of macadamia husk compost (MHC) on selected chemical and physical properties of a sandy loam soil in NE South Africa in two successive seasons. The treatments, laid out in randomised, complete block design and replicated four times, were: (i) zero control, (ii) inorganic fertilizer (100:60:60 NPK Kg ha⁻¹), (iii) MHC at 15 t ha⁻¹, and (iv) MHC at 30 t ha⁻¹. Soil bulk density; water holding capacity; soil pH; electrical conductivity (EC); organic carbon; total N; and available P, K, Ca, Mg, Al, Zn, and Cu were determined at 0–15 cm soil depth. Macadamia husk compost application decreased bulk density and increased water holding capacity. MHC and inorganic fertilizer increased soil pH, organic carbon, total N, C:N ratio, available P, exchangeable cations, and micronutrients but the effect was more pronounced under MHC treatments in both seasons. The positive effect of MHC on soil physicochemical properties was associated with an increase in soil organic carbon due to MHC application; hence, MHC may offer a sustainable option of increasing soil productivity, particularly in areas characterised by low SOC.

There is a dearth of information on the effect of macadamia husk compost (MHC) on the productivity of short-season, shallow-rooted annual crops. We assessed the response of yield and nutrient uptake of Chinese cabbage (Brassica rapa L. Chinensis) to MHC application. The treatments (zero control, inorganic fertilizer (100:60:60 kg NPK ha⁻¹), and 15 and 30 t ha⁻¹ MHC) were arranged in a randomized complete block design and replicated three times. Number of leaves, leaf area index, leaf biomass, and leaf nutrient concentration (N, P, K, Ca, Mg, Zn, Cu, Mn, and B) were determined at 28, 46, and 74 days after transplanting (DAT), and root length and root biomass were determined at 74 DAT. Inorganic fertilizer and MHC increased root biomass and root length with greater increases recorded at the higher MHC rates. Number of leaves, leaf area index, leaf biomass, and nutrient concentration were greater with application of inorganic fertilizer (28 DAT) and 30 t ha⁻¹ (74 DAT) suggesting that the effect of organic soil amendments is more pronounced over the long run compared with inorganic fertilizers. The concentration of macronutrients in the leaf increased with application of MHC and inorganic fertilizer. Clearly, MHC may be beneficial in improving the leaf yield and nutrient uptake of Chinese cabbage in a loamy sand soil, but the effect varies with time of harvesting.