The effect of legume cover crops on soil phosphorus availability
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abstract
Legume can fix atmospheric N and sequester carbon. Some legumes are able to uptake sparingly
soluble soil phosphorus. Additionally, all those effects may contribute to a beneficial increase in
soil microbial activity. In this work three ground-cover treatments were imposed to an olive
orchard located in NE Portugal: Natural vegetation (Nat veg); Natural vegetation fertilized with
60 kg N ha-1 yr-1 (Nat veg +N); and a mixture of self-reseeding annual legumes (Legumes). Three
years after the establishment of the ground-cover treatments, soil samples were taken from the 0-
10 and 10-20 cm depths. Extractable soil P was determined by the Olsen and Egner-Riehm
methods, the acid phosphatase activity accordingly to Tabatabai and Bremner and soil organic
carbon by the Walkley-Black method. In the 0-10 cm soil layer, the acid phosphatase activity was
significantly higher in the treatments Legumes and Nat veg+N (7.81 and 7.30 f-Lg p-Nitrophenol
g-1
) than in the Nat veg (4.73 f-Lg p-N g-1
). Considering both soil layers, there was observed a
significant linear relationship between oxidizable organic C and the acid phosphatase activity
(R2=0.69). The P extracted by the Egner-Riehm method was better correlated \vith the acid
phosphatase activity (R2=0.42) than P extracted by the Olsen method (R2=0.31) when all samples
were taken into account. It seems that a similar effect of the legumes species on the add
phosphate activity may be achieved with the natural vegetation if fertilized with N.
