Nutritional disorders of sorghum

• Indian Council of Agricultural Research, India

Grain sorghum is among the world's major staple foods, particularly in the semi-arid tropics. However, nutrient deficiencies severely limit production in both Africa and Asia, where the crop grows on a diverse range of soils. a recent ICRISAT symposium, 'Sorghum in the Eighties', established that information on the symptoms of various nutrient disorders of sorghum is not readily available, while even less is available on critical nutrient concentrations associated with either deficiencies or toxicities.
The aim of this project is to produce a colour-illustrated booklet containing all such information. A programmed nutrient-addition solution culture technique develop at the University of Queensland will form the basic approach, as it offers advantage in the control of nutrient supply and the wide range of elements that can be studied.
In this technique, scientists grow the plants for extended periods in 22-litre pots of nutrient solution, programming the supply of all nutrients to plant demands. Periodically, they reduce the levels of an element under study below full supply, producing growth reductions and the development of deficiency symptoms. After separating plant tops (harvested at an appropriate stage of growth) into a range of index tissues, they dry, digest and analyse these separately to determine the relations between dry matter production and nutrient concentration, at any stage of growth, corresponding to a given yield. The project will direct attention to both diagnostic and predictive use of critical concentrations, with emphasis on those elements reported as major limitations to field production of sorghum.
Sorhum, as a crop of the semi-arid tropics, often faces water stress and its consequent restrictions on growth. Moderate water deficits have reduced phosphate and sulfate transport to plant tops in other species, suggesting that the water stress may cause nutritional disturbances that contribute to the reduce growth. Scientists in this project will study the effects of water stress on nutrient absorption and, more particularly, on critical nutrient concentrations in sorghum. Initially, they will use high-molecular-weight polyethylene glycol to impose water stress on solution-grown plants. Emphasis will focus on a limited number of essential elements, including nitrogen, phosphorus and sulfur, relevant to the production of sorghum is lesser-developed countries, and on three important growth stages: floral initiation; anthesis; and grain fill.
Glasshouse experiments with specific soils known to lack an essential element will supplement the solution trials, also in Brisbane. Field-growth sorghum in India will provide material for the colour illustrations in the handbook, in a collaborative effort between Australian and Indian scientists and Dr Clark of Nebraska, who has accumulated a wide range of photographs of nutrient disorders in sorghum.