In one of our field experiments in South Africa, we are looking at the production of moringa leaf powder with moringa trees spaced 1 (within row) X 3 (between row) meters and managed as a hedge. We are able to get two cuttings of leaves each year. During each of these two harvests, the trees are pruned back to a height of 1 meter, with the cut branches left on the ground as mulch. Other than moringa prunings, the trees received three applications of chicken manure [2.0% nitrogen (N); 0.9% phosphorus (P); 1.9% potassium (K)] over the course of the growing season, amounting to a total-season rate of 266 kg/ha N, 120 kg/ha P, and 251 kg/ha K. A high rate of manure was applied in an effort to stimulate as much moringa growth as possible before the dry winter season.
To gain an understanding of the value of moringa prunings as a soil fertility input, we wanted to know the concentration of N, P, and K in woody versus leafy biomass of moringa trees. Plant tissue was collected at the second leaf harvest, about 2 months after the final manure application.
Dry leafy tissue contained 4.8% N, 0.5% P, and 1.9% K. Dry woody tissue contained 1.7% N, 0.6% P, and 3.1% K. As expected, N was more concentrated in leaf (4.8%) than woody (1.7%) tissue; however, the 1.7% N in woody tissue compared well to the 2% N in the chicken manure. Interestingly, the 3.1% K in woody tissue exceeded the 1.9 % K in leaf tissue and compared well with the 2%-5% K found in banana leaves.
Though nutrient concentrations may have been lower with less manure applied, these findings illustrate that there is mineral content in moringa stem/branch prunings that can contribute to soil fertility if left on the ground.