Effect of native soil fertility and mineral fertilizer on growth of pine seedlings in Uganda

Abstract

Commercial tree planting in Uganda is constrained by a lack of good quality seedlings due to poor soils used in nurseries. Two experiments were carried out; to evaluate the effects of different soils on the growth of the pine seedlings (experiment 1) and to compare the performance of seedlings provided with different NPK fertilizer formulations and amounts (experiment 2). Soils were collected from four forest reserves: Katugo (K), South Busoga (S), and Mbarara (M) and from Mubende forest reserve. Treatments were: 0, 0.5 kg and 1.0 kg levels; NPK fertilizer formulations 25−5−5 (A), 17-17-17 (B) and 18−4−14 +TE (C) mixed in 1 m 3 of soil. Composite soil samples were taken for laboratory analysis. Experiments were laid out in a completely randomized block design, but with a factorial treatment structure for experiment 2. Routine nursery management practices were carried out. Seedling heights and diameter were recorded. The results showed that SOM (site 1), total N (site 2) and available P, K, Ca and Mg were below the critical values. Low nutrient concentrations reduced growth, with seedling height highest in Katugo and girth highest in the Mbarara. Results of experiment two showed that there were no significant differences in mean heights for fertilizers A and C after a 1½ months application and B had a significant difference in the mean height and girth. However, fertilizer C girth results were significant with (Pvalue = 0.021, Pvalue = 0.001) at 1½ months and 3 months respectively. After 3 months, fertilizer B had the best mean height and mean girth at level 0.5 kg with (16.75 cm, 0.23 cm) re- spectively, compared with fertilizer C and A with (13.42 cm, 0.175 cm) and (12.44 cm, 0.174 cm) respectively. From the results, a general NPK fertiliz- er formulation 171717 is recommended for use at a rate of 0.5 kg m 3 of soil.