Effect of Solid Phosphate Sludge Amendments on the Growth of Fruit and Forest Trees in the Nursery

Phosphorus deficiency is a major limiting factor in horticultural production. One potential solution can be restoring soil phosphorus from mineral resources, such as solid phosphate sludge (SPS) generated from phosphate treatment processes at mining sites in agriculture. This study explores the possibility of using this sludge in nurseries to produce fruit and forest plants. We tested six mixtures of SPS with the sandy soil of the Maamora forest on ten plant species. In the second experiment, we tested the same mixtures with sea sand. In addition, one concentration of four composts based on phosphate sludge was also tested on two citrus rootstocks and carob. The first experiment's results showed significantly higher growth with the control mixture for pomegranate, acacia, and C. volkameriana plants. The relative growth was higher at SPS concentrations of 20% to 30% for the other plant species, although there was no significant difference between treatments. The estimations of AUGPC (area under the growth progress curve) showed no significant difference in most species. In the second experiment, the relative growth in the M4 (30% of SPS + 70% of sand) mixture was higher, and the AUGCP showed a significant difference compared to the M1 control mixture. The application of solid phosphate sludge positively affects and improves the growth of fruit and forest trees in the nurseries, especially when the concentration is between 20 and 30%. For this purpose, the phosphate sludge could have great potential to be used in nurseries and create a favourable soil condition as a cultivation substrate.