ANALYSIS OF WATER BALANCE FOR DETERMINE CROPPING PATTERNS FOR FOOD CROPS IN WATERSHED ARANGMUMUS THE PROVINCE OF EAST KALIMANTAN

The experiment objectives was to determine cropping patterns of food crop in watershed Karangmumus. The geographical position 116º 49' EL ? 117º 08' EL dan 0º 34' SL ? 0º 45' SL, with extent of the 644.2 km2 whereas covers 8 village or 38.58% of total Samarinda City. Have the Area Class III (1500 ? 2000 mm/ year,. with the Bimodel or Double Wave rainfall models with C patern. The hight rainfall depth periode at December and April, therefore the low rainfall depth at September and November. Have a value Q = ± 9.9%, or rainfall tipe A (very wet area with tropical wet vegetation) and E1 agroclimtic zone. Modified method of Thornthwaite and Mather of bookkeeping system of water balance was used based on monthly data. Water Balance monthly indicated that this area have potential growing season about 9 months, have to water surplus 7 month (478, 8 mm year-1 ) and water deficits about 4 months (44.5 mm/year). In these area rice could be planted twice a year without irrigation. Futher for non-irrigation land with monthly high rainfall, the result showed that the area had potency of growing periods of 182 days through the year. Planting dates might be started from October 1 until December 1, with sequence of rice-rice or rice-rice-other food crops.