Response of the growth and survival of tree species planted in a degraded land with a supplement of diammonium phosphate (DAP) fertilizer

Degraded lands pose significant challenges for tree establishment and growth due to poor soil quality and limited nutrient availability. This research aims to explore the potential of using DAP (diammonium phosphate) fertilizer as a supplement for enhancing the survival and growth of tree species in degraded lands; Casuarina equisetifolia L., Grevillea robusta var. robusta R.Br., and Olea europaea subsp. cuspidata (Wall. & G. Don). To achieve the objectives, seedlings of the species were planted in degraded land using a randomized complete block design (RCBD), with a supplement of DAP fertilizer. Six replications, each consisting of 20 seedlings, were used for each of the species with the DAP treatment. The survival and growth data were collected from January 2015 to May 2022. One-way ANOVA, t-test, and mean survival percentage were used for data analysis. The results revealed that the mean final survival percentage of C. equisetifolia that received DAP fertilizer (73.6%) was higher than that of C. equisetifolia without fertilizer (44.4%). The statistical t-test also showed significant differences between the mean survival percentages of C. equisetifolia planted with a supplement of DAP and without fertilizer (p = 0.033). The mean survival percentage of O. europaea and G. robusta, whether fertilized or not, was poor (0%-7%). The one-way ANOVA result showed significant differences in both fertilized and unfertilized seedlings among the C. equisetifolia, G. robusta, and O. europaea species (p < 0.001). The dry biomass of C. equisetifolia grown with a supplement of DAP fertilizer and the unfertilized was 15.4 kg/tree and 11.2 kg/tree. The t-test result revealed no significant differences in the dry biomass of the C. equisetifolia grown with a supplement of DAP fertilizer and without fertilizer. Finally, it is concluded that the effect of DAP fertilizer on the growth and survival of the species is species-specific.