Abstract Back to Table of contents
Studies were conducted in Maroua under Sudano-Sahelian conditions to estimate the effects of sowing date and nitrogen application on petiole nitrate content of cotton. The dry weight and petiole nitrate content of the 4th leaf from the top of the canopy of cotton plants were measured at three day intervals. During the observation period and for all treatments, the petiole had a rapid weight gain phase followed by constant weight phase. Application of nitrogen on the early sowing date did not significantly increase the petiole nitrate content when compared with the control. On the other hand, the application of nitrogen on the late sowing date and before flowering, increased the petiole nitrate content but this remained low when compared with that of the early sowing date of the same age. The change in nitrate content observed was not linked to the increase in weight of the fourth leaf. In Maroua conditions, the change in petiole nitrate content during the vegetative cycle differs from that described in the literature.
Discussion and Conclusion
Nitrogen application had an effect on the petiole weight when cotton was sown late, which confirms knowledge on the effect of nitrogen. However, the absence of weight differences between control and nitrogen application for the early sowing date indicates that there was no effect on the growth of the organ. Sowing date and nitrogen application have an important action on the growth of leaves and determining leaf number on the main stem. The increase in petiole nitrate content while the weight of this organ is also increasing shows that the nitrate content is not at this time affected by the dry matter increase. The decrease observed during the flowering period seems to be related to important needs of nitrogen at each flower or boll. The late application of nitrogen is not sufficient to increase the level of petiole nitrate content as occurs during the early sowing date. Observations by Richard (1980) are not confirmed when cotton is sown earlier this shows that petiole nitrate content depended more on the quantity of nitrogen applied, sowing date and date of nitrogen application than on the increase of dry matter weight. This can be helpful in the interpretation of results of the diagnosis.