Effects of green manure and coral lime on corn growth and chemical properties of an acid Oxisol in
D. J. Hunter, L. G. G. Yapa, and N. V. Hue
Effects of local green manure (GM) and lime on soil productivity in a low-input agricultural
system were evaluated by growing three successive crops of sweet corn (Zea mays) on an acid Oxisol (Typic
acrorthox, Togitogiga series) in Western Samoa. The soil was amended with coral lime 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 prior to planting of the first crop.
Response parameters measured included nutrient composition of leaves at tasseling and grain yield of each
crop, and selected soil chemical properties at each planting. Yields of the first crop were nearly tripled
with GM additions and doubled with 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 declines were much steeper for the GM treatments than for the lime treatments.
Thus, the enhancement effect on K nutrition did not last beyond one crop. Poor growth of the second and
third crops was caused by K deficiency; probably coupled with Mn toxicity. Significant yield reductions
were found when Mn-to-K ratios in leaves exceeded 0.010. As for effects on soil, soil pH was increased
significantly by lime but only slightly by GM. Given the variable charge property of this Oxisol, each unit
pH increase corresponds to a CEC increase of 5 cmolc 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 cmolc kg-1 of exchangeable soil K or 7% of CEC for adequate growth.
Biology and Fertility of Soils. 1997 (in press).
COMPARATIVE EFFECTS OF GREEN MANURE AND LIME ON THE GROWTH
OF SWEET CORN AND CHEMICAL PROPERTIES OF AN ACID
OXISOL IN WESTERN SAMOA
D.J. Hunter, L.G.G. Yapa, N.V. Hue and M. Eaqub
Commun. Soil Sci. Plant Anal. 26:375-388 (1995)
Liming values of calcium carbonate (CaCO3) and cowpea green manure were evaluated
on an acid Oxisol (Typic Acrorthox, Togitogiga series), based on seed yield and tissue
composition of sweet corn (Zea mays), and soil chemical properties. Application rates
were 0, 5, and 10 Mg/ha for CaCO3 and 0, 7.5, and 15 Mg/ha for the green manure,
factorially arranged. Treatments with commercial NPK fertilizers were included for
comparison. Growth and yield of sweet corn showed that soil acidity can be corrected by
either lime or green manure additions. Both lime and manure raised soil pH and (modified
Truog) extractable phosphorus (P), which were partially responsible for yield increases.
Green manuring significantly increased plant P and potassium (K) concentrations, which
explain why the manure was more effective than lime in increasing corn yield. Ear leaves
sampled at tasseling required at least 0.25% P and 2.4% K to attain >90% of the maximum
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