Phosphorus fertilization in sugarcane ratoon and its interaction with magnesium

There are still doubts with regard to the efficiency of P fertilization in the sugarcane ratoon and the interaction between P and other nutrients that could affect the responses to P reapplication. An experiment was set up to evaluate the effects of P rates (45 and 90 kg ha(-1) of P2O5) applied either in the absence or presence of Mg fertilizer (50 kg ha(-1) of Mg) on the stalk yield, of sugarcane ratoon. P fertilization increased stalk yield in 17% compared to the control treatment (no P fertilizer). However, such response did not depend on Mg fertilization, suggesting that Mg was not critical to the occurrence of P response. The P nutritional status of sugarcane was not also affected by Mg application, being altered exclusively by P fertilization. P content in the leaves varied significantly (p<0.05) from 1.4 g kg(-1) in the control to 1.7 g kg(-1) and 1.9 g kg(-1) in the treatments with application of 45 and 90 kg ha(-1) of P2O5, respectively. P fertilization increased in 21% and 16%, the efficiency in the use of N and K fertilizers, respectively, compared to the control. The results suggest that increases in the yield of sugarcane ratoon cultivated in a low-P soil can be obtained with P reapplication, what might be related to the improvements on the P nutritional status of the plants.