Abstract

RIVERA O., Patricio et al. Acid-Iron Fertigation of Citrus Established in Calcareous Soils. Terra Latinoam [online]. 2008, vol.26, n.2, pp.119-125. ISSN 2395-8030.

In most calcareous soils, iron solubility is low. For this reason, crops growing in these soils often exhibit iron deficiency. The objective of this research study was to determine the influence of acidification of irrigation water on the downward movement of Fe and its availability for citrus trees. The test was conducted in three phases. During the first phase, under controlled conditions, 1 and 3% solutions of 100 mg L^-1 Fe dissolved in water and H₂SO₄ were dripped onto the surface of 4 cm thick and 6 cm diameter columns of soil for 14 h. In the second phase, pots containing 1.5 kg soil, planted with 'Cleopatra' mandarin (Citrus reticulata) seedlings, were treated with 0, 100, 200 and 300 mg L^-1 Fe (as FeSO₄) dissolved in 3% H₂SO₄ applied at a soil depth of 3 cm. In the third phase, over a period of three years the soil surrounding 12-year old adult 'Valencia' orange trees (Citrus sinensis) was treated each year with 120 kg ha^-1 FeSO₄, together with 450 and 900 kg ha^-1 H₂SO₄, dissolved in irrigation water applied by micro-spraying. Fe applied in a nonacid solution on the surface of the soil columns did not descend, but when applied in acid solution its movement was significant in the first 2 cm. Beyond this depth, movement of the element was not observed. The Fe acid solutions applied in pots and in the field, although they lowered soil pH, did not correct iron chlorosis in citrus trees nor did they increase leaf Fe concentration or fruit yield. The null response of the citrus trees to acid Fe fertigation was due to the high soil calcium carbonate content that neutralized acidity of the solution applied, causing the element to precipitate. For these reasons, the practice cannot be recommended.

Keywords : calcium carbonate; sulfuric acid; acidification; iron chlorosis.