Glomalin: a potential soil quality indicator for Philippine uplands
2002
Almendras, A.S. (Leyte State Univ., Baybay, Leyte 6521A (Philippines). Dept. of Agronomy and Soil Science) Wright, S.F.
Declining soil quality in several Philippine farmlands is often attributed to continuous cropping. The growing awareness of the progressive soil degradation triggered the search for a reliable and objective measure of soil quality. Evidences showed that biological and biochemical properties are sensitive indicators to changes in management practices hence fulfill the primary requirement for selection of indices for characterizing soil quality. Studies on temperate soils have shown that the impact of cropping system on soil quality can be assessed by measuring aggregate stability and glomalin compound. Glomalin is a glue-like compound produced by arbuscular mycorrhizal fungi. Evaluations of aggregate stability and glomalin status from soils under intensive cultivation and under natural vegetation was done. Soil samples (0-10 cm depth) were collected from cultivated grassland, undisturbed and disturbed forests, and sweet potato and corn fields. Fractions of glomalin measured were: easily extractable (EEG), total (TG) and the amount of immunoreactive glomalin (IREEG and IRTG) in each fraction. Stability was measured using two methods: the normalized stability index (NSI) and the bulk soil and % stability of air dried aggregates subjected to wet sieving for 5 minutes. The glomalin content varied among soil samples with the soil from the field continually grown to sweet potato had the lowest values in all glomalin requirements. NSI aggregate stability was linearly correlated with EEG (r square = 0.78). However, % stability of 1-2 mm aggregates was not correlated to any of glomalin fractions. Results of this study show that NSI aggregate stability compared with EEG are the best soil quality indicators
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