EVIDENCE FOR DIFFERENT NITROGEN USE EFFlClENClES OF SELECTED SUGARCANE VARIETIES

A rapid screening (hydroponic) and field testing programme There is increasing interest in improving the nitrogen (N) use efficiency of cultivated crops, due to the high cost of synthetic N fertiliser. Since existing differences in N use efficiency between sugarcane varieties could be exploited to improve N fertilisation, a hydroponic pot experiment was conducted to test the performance of seven commercial South African varieties (NCo376, N12, N14, N16, N19, N24, N25) at three N concentrations (30, 60, 90 mg NL). At the first N increment, significant varietal differences in internal N use efficiency (g sucroselg accumulated N) were recorded in the ratoon cane. High N use efficiencies for N12 and N19 were 65 and 63% respectively, above the 'reference' variety NCo376. In contrast, N14 was 19% less efficient than NCo376, which is in agreement with results from field trials. These data suggest that substantial benefits may be derived from variety specific N fertiliser recommendations for sugarcane, rather than a single recommendation based on NCo376. Based on field trial data, fertiliser recommendations for N14 have recently been increased by 30 kg Nlha. The hydroponic technique should be useful for initial screening of the many commercial and new sugarcane varieties before final field testing and amendments to fertiliser recommendations.