The effects of lime and phosphorus on the function of wheat roots in acid top soils and subsoils

Abstract

Two wheat varieties with differing aluminium tolerance were grown in pots of acid soil. Liming did not change significantly the amounts of chemically extractable P and K, but caused improved vegetative growth, increased inflow of P and K and reduced uptake of AI. Without lime, roots had a higher content and concentration of P than shoots; liming reversed this. Without lime the sensitive variety with a shorter root length had an AI inflow ten times that of the tolerant one: tolerance involves a mechanism for exlcuding AI. The inflow of P per unit inflow of A1 (mol ratio) without lime was three times greater for the tolerant variety which therefore has more P to counteract the effects of A1.The same varieties were grown in two-layer soil columns, with a low P status and a limed topsoil and acid subsoil. Liming the subsoil improved plant growth but this was still restricted by low P availability. Addition of P to the topsoil caused good growth regardless of subsoil acidity: root growth increased in both layers and P (labelled with 32p) taken up from the topsoil was translocated to roots in the subsoil. This P inactivated root AI and allowed the roots to grow and take up more P from the acid subsoil with however a reduction in inflow. The sensitive variety was affected more by the acid subsoil and low P availability, had a similar ability to translocate P to subsoil roots but could not attain the growth rate of the tolerant wheat even with P and lime.

Soil Chemical Factors Limiting Plant Root Growth

“…Does P deficiency in the subsoils limit root growth? DeMiranda and Rowell (1987) found that liming subsoils improved plant growth, but yield was still limited by low P availability. Additions of P to the topsoil (presumably with adequate soil moisture) caused good growth regardless of subsoil acidity.…”

Multiple Aluminum-Resistance Mechanisms in Wheat (Roles of Root Apical Phosphate and Malate Exudation)

“…Pellet, unpublished data). It has also been shown that the application of Pi fertilizers to surface soil horizons enhanced the ability of plant roots to penetrate the surface soil horizons and to enter acidic subsoils, where A1 concentrations limit root growth (Miranda and Rowell, 1987;McLaughlin and James, 1991). According to the authors, Al-phosphate formation was a possible cause for this beneficia1 response.…”

Capacidade de absorção de nutrientes do capim-mMarandu (Brachiaria brizantha) e da planta daninha malva (Urena lobata) em função do pH

“…Freqüentemente, esses solos apresentam baixa disponibilidade de nutrientes, e o alumínio tóxi-co impõe restrições ao desenvolvimento das raízes, ao mesmo tempo que reduz a absorção de nutrientes (Miranda & Rowell, 1987). Em razão desse aspecto, a capacidade que as plantas forrageiras devem possuir para vegetar satisfatoriamente nessas condições, principalmente em relação às plantas daninhas que infestam essas áreas, é crucial para a manutenção da produtividade elevada da área.…”