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 pla nt growth on terra rossa is limited by phosphorus deficiency; (b) that shrub control and tree thinning can release available P for use by he rbaceous vegetation; (c) that cattle fed P-rich poultry litter as a ni trogen supplement, can increase the available P level in the soil by r ecycling excess P through their excrements. Soil available P (bicarbon ate-soluble) content was 4-9 mg kg-1 soil in the surface 15 cm soil la yer and 2-3 mg kg-1 soil in the deeper 15-30 cm layer. A bioassay show ed 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 ha d 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 yea rs by cattle supplemented with poultry litter. Only near centers of ca ttle activity was there a significant increase of P in the 3-15 cm lay er, and only there was the enrichment sufficient to remove phosphorus limitation to herbage growth.