The significance of root growth on cotton nutrition in an acidic low-P soil

Toxic levels of Al and low availability of Ca have been shown to decrease r oot growth, which can also be affected by P availability. In the current ex periment, initial plant growth and nutrition of cotton ( Gossypium hirsutum var. Latifolia) were studied as related to its root growth in response to phosphorus and lime application. The experiment was conducted in Botucatu, Sao Paulo, Brazil, in pots containing a Dark Red Latosol (Acrortox, 20% cla y, 72% sand). Lime was applied at 0.56, 1.12 and 1.68 g kg(-1) and phosphor us was applied at 50, 100 and 150 mg kg(-1). Two cotton (cv. IAC 22) plants were grown per pot for up to 42 days after plant emergence. There was no e ffect of liming on shoot dry weight, root dry matter yield, root surface an d length, but root diameter was decreased with the increase in soil Ca. Sho ot dry weight, as well as root length, surface and dry weight were increase d with soil P levels up to 83 mg kg(-1). Phosphorus concentration in the sh oots was increased from 1.6 to 3.0 g kg(-1) when soil P was increased from 14 to 34 mg kg(-1). No further increases in P concentration were observed w ith higher P rates. The shoot/root ratio was also increased with P applicat ion as well as the amount of nutrients absorbed per unit of root surface. I n low soil P soils the transport of the nutrient to the cotton root surface limits P uptake. In this case an increase in root growth rate due to P fer tilisation does not compensate for the low P diffusion in the soil.