Solid phosphate sludge composted with organic horticultural residues improves the growth of citrus and forest seedlings

The main environmental challenges of phosphate mines are the huge amounts of waste generated as solid phosphate sludge. These contain a high phosphate rate which is necessary for agriculture production, but chemical parameters as presence of heavy metals and pH make its use possible with limited quantity. In order to be recovered for organic nursery use as a source of phosphorus, different mixtures with organic horticultural wastes in Souss-Massa Region of Morocco were tested in 220-L bioreactors. The objective was to assess the effect of composted phosphate sludge with organic horticultural residues on citrus and forest seedling growth. Solid phosphate sludge with proportions of 41, 29, 35, and 10% (w/w) was mixed with tomato waste, consisting of stems and leaves along with sheep manure (B1, B2, B3, and B7, respectively). Composts were prepared, and 4 weeks after maturity, they were used for plant growth studies using citrus rootstock (Carrizo citrange), carob (Ceratonia siliqua), and argan (Argania spinosa) plants under glasshouse conditions. The experiment was conducted in El Menzeh station of Regional Center for Agricultural Research in Rabat-Sale-Kenitra Region of Morocco. All composts were applied at different concentrations of 0, 5, 10, and 20% (v/v) with sandy soil of Maamora Forest. B7 compost applied at 10% showed significant increase in relative growth of C. citrange plants compared to control soil. Furthermore, application of 5% rate of B3 and B1 enhanced relative growth for argan and carob plants, respectively. Similarly, estimates of the area under the growth progress curves (AUGPC) showed an increase of area when B7 compost of 10%, B3 compost of 5%, and B1 compost of 5% were applied. The study shows that the application of composts as an amendment can increase the performance of substrates which leads to improving citrus and forest seedling growth.