Aiming to reproduce leaf yellowing symptoms observed on upland rice grown under field conditions, in Assis county São Paulo State, Brazil and to study its possible nutritional causes, a greenhouse pot experiment was carried out at the Instituto Agronômico, Campinas county. The treatments involved a quartz sandy soil collected from 0-20cm top layer submitted to two cropping systems (original soil, and limed and cultivated soil), two types of irrigation (standard and excessive) and four rice cultivars (IAC 25, IAC 47, Araguaia and Rio Paranaíba). Evaluated were symptoms of leaf yellowing, the dry matter accumulation of shoot parts (leaves and culms) and root, macro and micronutrients concentrations in leaves and culms. Also studied were some anatomic characteristics of leaves and roots. Using standard irrigation almost no yellowing occurred in both soils. However, with excessive irrigation of the original soil, leaf yellowing symptoms and an increase on shoot: root dry matter ratio occurred. In the original soil, drenching caused increases on the Fe concentrations in the shoot parts (leaves and culms) and decreases on the Mn concentration in the leaves and culms. In the cultivated soil, the results were similar except for Fe concentration that decreased in the leaves. The cultivars Araguaia showed the lowest ratings of yellowing and a tendency to have higher values of N, P, and Ca than the others cultivars, and it was the only one to which excessive irrigation did not decrease the Mn values in the leaves. In the leaf blades from plants of the original soil treated with excessive irrigation the chloroplasts were smaller, distributed in the peripherical region of the mesophyll cells and were in smallest number than those of the others treatments. It was concluded that the leaf yellowing occurred under drenched low fertility soil conditions due to both plant Fe toxicity and Mg deficiency, and it could be associated to a multiple nutritional stress. From the cultivars tested, Araguaia was more tolerant to the adverse soil conditions inducing leaf yellowing.
upland rice; nutritional deficiency; soil drenching; leaf yellowing