Pc. Smithson et al., Nitrogen and potassium fertilizer vs. nematode and weevil effects on yieldand foliar nutrient status of banana in Uganda, NUTR CYCL A, 59(3), 2001, pp. 239-250
Banana (Musa AAA) production is declining in central Uganda. A decline in s
oil fertility is often cited as one of the causes of the declining producti
on. From 1996 to 1998, we studied banana yield responses to N and K fertili
zation at three sites in Uganda, where plantations ranged in age from 8 to
50 years. Phosphorus was applied to all treatments at 25 kg ha(-1), while N
and K were applied (kg ha(-1)) at ON-OK, ON-100K. 100N-0K, 100N-100K, and
100N-200K. Fresh fruit yields ranged from 4 to 67 Mg ha(-1) yr(-1). At one
site the yield response to 100N-100K fertilization was significant (p<0.01)
. The other sites showed positive but non-significant yield responses to N
or NK fertilization. Economic analysis indicated that fertilizer use would
be profitable only at the single site with significant yield increases. Thi
s site had negligible banana weevil (Cosmopolites sordidus (Germar)) and ne
matode (Radopholus similis; Helicotylenchus multicinctus) populations where
as the other sites were characterized by either severe nematode or weevil p
ressure. Fertilizer did not affect the damage caused by either nematodes or
weevils. The best predictor of yield (p<0.001, r(2)=0.75) was the number o
f functional leaves during anthesis. Measured soil nutrient parameters were
highly variable but fell within sufficiency ranges. Foliar N contents were
near diagnostic norms, but K levels fell below them, even when yields were
satisfactory, suggesting that norms developed froth other regions may not
be suitable for Uganda. We conclude that in established plantations soil nu
trient status is but one, and often a secondary, factor in the decline of b
anana yields in the central region of Uganda. Pest and disease infestations
that result in reduced plantation productivity will need to be addressed b
efore fertilizer use is likely to make a significant improvement in banana
fruit yields.