STUDIES ON IRON CHLOROSIS OF SUGAR-CANE (SACCHARUM-OFFICINARUM L) AT METAHARA, ETHIOPIA - SOIL AND PLANT CHARACTERIZATION AND EFFICIENCY OFDIFFERENT IRON SOURCES

In order to understand the nature and causes of chlorosis at Metahara Sugar Estate (8 degrees 53'N and 39 degrees 52'E) in Ethiopia, soil pr ofile samples were collected from a ratoon field that exhibited chloro sis. From the same site, the first ratoon sugar cane leaf blades (+3) were sampled on the basis of the degree of chlorosis, and thus categor ised into green, medium green, medium yellow and yellow. Soil sample a nalysis indicated that DTPA-extractable Fe, Mn and Cu were adequate fo r normal plant growth in spite of an increase in CaCO3 content. Moreov er, the chlorotic leaves contained higher iron content than the green ones. Consequently, it is concluded that iron chlorosis of sugar cane at Metahara could be due to physiological inactivation of iron in soil s and the plant. A field experiment was also conducted using sugar can e variety CO-449 in order to select the most effective iron source to control iron chlorosis of the plant. The plots received the treatments of FeSO4, EDDHA and DTPA at three different levels each as foliar spr ays. The untreated plots were used as control. The chemicals were appl ied on the first ratoon 3 weeks after harvest, and repeated a week aft er the first spray. Twenty millable canes from the middle two rows wer e sampled at 12 months for yield and juice quality determinations. Iro n sulphate spray at 15 kg ha(-1) increased cane length and commercial cane sugar by 33 and 44 % over the control, respectively. The highest cane yield was secured by spraying DTPA at 1.80 kg ha(-1) even though its recoverable sugar percentage was low. Not all sources of iron impr oved juice quality. Since FeSO4 at 15 kg ha(-1) was equally effective as the 30 kg ha(-1) FeSO4 applications, the need to consider other tha n the currently used rate in the Estate is timely and is very importan t.