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Contribution of organic fertilisers to nitrogen nutrition in sugarcane and nitrate leaching in sugarcane agroecosystems in Réunion

Poultney D., Versini A., Detaille C., Feder F., Thuriès L.. 2019. In : Proceedings of the XXX International Society of Sugar Cane Technologists Congress. Tucuman : ISSCT, p. 1205-1215. ISSCT Congress. 30, 2019-09-02/2019-09-05, Tucuman (Argentine).

Nitrogen is essential to crop growth and development in sugarcane agroecosystems and mineral fertilisers are frequently used to meet crop N demand. However, in excess, N has negative environmental consequences. Organic fertilisers may be a good alternative or complement to mineral fertilisers by reducing the loss of excess N, and thereby minimising the negative environmental consequences. The aim of this study was firstly to determine the contribution of two types of organic fertilisers (sewage sludge and pig slurry), compared to a mineral fertilizer (urea), on sugarcane N nutrition and nitrogen-use efficiency. The second objective was to evaluate N loss from the sugarcane agroecosystem by assessing nitrate (NO3) flux. The study was undertaken in Réunion. Sugarcane N nutrition was studied by determining the respective contributions of mineral fertilisers, organic fertilisers, mulch, roots and soil to crop N throughout the crop cycle. The N-fertiliser recovery efficiency (REN), a quantitative indicator of nitrogen-use efficiency, was also estimated for these N sources. Nitrate leaching in the soil was studied using porous cups under tension at depths of 10 cm; 40 cm and 100 cm. The results show that most of the N nutrition in the sugarcane was provided by the soil. The N-fertiliser recovery efficiency of urea was higher than with the organic fertiliser treatments. The sewage sludge appears to have been released more gradually and its REN increases close to that of the urea treatment before the second application of urea. There is a relatively low but stable contribution to the sugarcane nutrition from mulch. The low nitrate concentrations at a soil depth of 100 cm suggest that N was conserved in the soil. However, given the high concentration of nitrates of pig slurry at 10 cm and 40 cm, this fertiliser is clearly dynamic and should be monitored carefully during high rainfall periods.

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