Soil phosphorus in a managed Mediterranean woodland ecosystem: herbage response and cattle grazing effects

A study of soil-plant relations in scrub woodlands on terra rossa soil in Israel, examined the following hypotheses: (a) that herbaceous plant growth on terra rossa is limited by phosphorus deficiency; (b) that shrub control and tree thinning can release available P for use by herbaceous vegetation; (c) that cattle fed P-rich poultry litter as a nitrogen supplement, can increase the available P level in the soil by recycling excess P through their excrements. Soil available P (bicarbonate-soluble) content was 4-9 mg kg^-1 soil in the surface 15 cm soil layer and 2-3 mg kg^-1 soil in the deeper 15-30 cm layer. A bioassay showed that plant growth was restricted when P concentration was less than 11 mg P per kg soil. Addition of nitrogen did not increase herbaceous yield, Neither thinning of trees nor shrub control using herbicide had any significant effects on available soil P. There was a significant increase in available soil P concentration in the surface 3 cm layer of soils on sites that had been partially cleared and grazed for 3 years by cattle supplemented with poultry litter. Only near centers of cattle activity was there a significant increase of P in the 3-15 cm layer, and only there was the enrichment sufficient to remove phosphorus limitation to herbage growth.