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 (R2
= 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.