RATTLE TREE (ALBIZIA LEBBECK) EFFECTS ON SOIL PROPERTIES AND PRODUCTIVITY OF IRISH POTATO (SOLANUM TUBEROSUM) ON THE JOS PLATEAU, NIGERIA

This study was carried out with the aim of assessing the rattle tree (Albizia lebbeck) effects on soil properties and Irish potato (Solanum tuberosum) productivity on the Jos Plateau, Nigeria. In carrying out the research, a randomized complete block design (RCBD) was employed consisting of five treatments and three replicates. The five treatments applied were as follows: Treatment 1 (T1): Irish potato planted in the alley (space) between A. lebbeck tree rows without green manure; T2: Potato planted without A. lebbeck tree rows but with its green manure application, two weeks before planting of potato at 5 ton/ha; T3: Potato planted in the alley of A. lebbeck tree rows with its green manure (as mulch) at 5 ton/ha; T4: Potato planted in the alley of A. lebbeck tree rows at 10 ton/ha and T0: Potato planted without A. lebbeck green manure and tree rows as control. Plot size was 3 m x 2 m (6 m2 ) in form flat bed. Apart from T3 with the green manure as mulch on the plot, the green manure applied to other treatments was ploughed with the soil. Green manure application was done two weeks before planting of potato and A. lebbeck seedlings were planted one week prior to planting of potato. The field experiment lasted for three years (2004 –2006) and both rainy and dry cropping seasons were carried out. The observations made include significant effect (P < 0.01) of the treatments, blocks, seasons and treatment x season (interaction) on the growth parameters (seedlings’ emergence percentage, plant height, leaf count and collar girth) and yield indices [tuber count (P < 0.05) and tuber weight (P < 0.01)]. T4 which had the highest level of green manure application (10 t/ha) with A. lebbeck tree rows emerged as the most effective treatment in terms of growth performance and optimal mean yield (10.24 t/ha). From the five cropping seasons, the mean yield from dry season harvests (7.89 t/ha) was higher than those of rainy season (7.73 t/ha). The independent variables (collar girth, leaf count and plant height) showed positive correlation with the dependent variable (Irish potato yield) while stem count had a negative correlation with yield. Very importantly leaf count and collar girth were the two determinants of yields (of this bertita variety of Irish potato) from this study. They accounted for 61.6 – 91.3% of the variation in yield (R 2 = 0.616 – 0.913). Similarly, improvement on soil nutrient status and significant effect of treatments and blocks on some soil properties such as available phosphorus (P) (at 0 -10 cm depth) and potassium (K) (0 – 10 cm and 10 – 25 cm depths) at P < 0.05 were observed. However, only block effect was recorded on pH and Mg and there was a general decrease in the organic matter, total nitrogen (TN), calcium (Ca), sodium (Na), exchangeable acidity and effective cation exchange capacity (ECEC) after planting. This could probably due to leaching, absorption by the crops and crop removal. Thus, it could be inferred that the green manure (at 10 ton / ha) and tree rows of A. lebbeck can improve soil nutrient status and productivity of this crop. Also, sustainable production of Irish potato without the use of nitrogenous / inorganic fertilizer under this agroforestry system is feasible on the Jos Plateau.