Dj. Hunter et al., EFFECTS OF GREEN MANURE AND CORAL LIME ON CORN GROWTH AND CHEMICAL-PROPERTIES OF AN ACID OXISOL IN WESTERN-SAMOA, Biology and fertility of soils, 24(3), 1997, pp. 266-273
Effects of local green manure (GM) and lime on soil productivity in a
low-input agricultural system were evaluated by growing three successi
ve crops of sweet corn (Zea mays) on an acid Oxisol (Typic acrorthox,
Togitogiga series) in Western Samoa, The soil was amended with coral l
ime at 0, 5, and 10 Mg ha(-1) and with cowpea GM at 0, 7.5, and 15 Mg
ha(-1). Commercial NPK fertilizers at 50 kg ha(-1) each of N, P, and K
were included for comparison. The amendments were applied only once p
rior to planting of the first crop. Response parameters measured inclu
ded nutrient composition of leaves at tasseling and grain yield of eac
h crop, and selected soil chemical properties at each planting. Yields
of the first crop were nearly tripled with GM additions and doubled w
ith lime additions. Such yield increases were caused mainly by better
K nutrition and to a lesser extent by enhanced P nutrition. Yields of
subsequent crops were much lower than those of the first, and the decl
ines were much steeper for the GM treatments than for the lime treatme
nts. Thus, the enhancement effect on K nutrition did not last beyond o
ne crop. Poor growth of the second and third crops was caused by K def
iciency; probably coupled with Mn toxicity. Significant yield reductio
ns were found when Mn-to-K ratios in leaves exceeded 0.010. As for eff
ects on soil, soil pH was increased significantly by lime but only sli
ghtly by GM. Given the variable charge property of this Oxisol, each u
nit pH increase corresponds to a cation exchange capacity (CEC) increa
se of 5 cmol(c) kg(-1). Having greater CEC, the amended soil retained
K more effectively, thereby causing yield increases, especially of the
first corn crop, which required at least 0.75 cmol(c) kg(-1) of excha
ngeable soil K or 7% of CEC for adequate growth.