Comparative Tolerance of Tropical Green Manure to Toxicity in Acid Sulfate Soils

Abstract

To determine th growth rates and tolerance of four green manures to A1 toxicity, a greenhouse study was conducted. Two acid sulfate soils (Bg : Typic Sulfaquepts; Ra : Sulfic Tropaquepts), high in "Aluminum", wereadjusted to four pH levels : 3.8 and 4.0 (original soil pH), 4.5, 5.5, and 6.5 Top dry weight was determined at the 49 day growth stage. Nitrogen, P,K, Ca, Mg, Al, Mn, and fe concentrations were also determined in top samples.
Soil pH levels affected the dry weight production of each green manures. Tolerant species showed a higher or similar dry weight yield at unamended soil pH or pH 4.5 compared to pH 6.5. The best dry weight yields at pH 6.5 were obtained with those species that were the most acid tolerance with Cajanus cajan and Sesbania aculeata, whereas Sesbania rostrata and Sesbania speciosa were the poorest.
Top analysis was used to determine total nutrient uptake and tolerances of a range of some green manures to excess A1. For all combinations of two soils, poor growth could largely be attributed to problem with A1 and Ca uptake. However, high levels of tissue A1 were probably the principal limitation to green manure growth at pH 4.5. Tolerance, based on teh critical A1 concentration at 90% of maximum growth (parentheses in mg kg-1), was of the order in Bg soil : C. cajan 960) S. aculeata (45) S. rostrata (39) S. speciosa (29); and in Ra soil : c. cajan (63) S. aculeata (54) S. rostrata (49) s. speciosa (40). these results are discussed in terms of current understanding of the nature and potential of A1 tolerance in various green manure species.