na INLIS000000000003198 0010-0121001564 The economics of rice-fish production sytems in North Sumatra, Indonesia Sirman Purba KIel Wissenschaftsverlag vauk kiel KG. 1998 x, 181 p. : ill.; 21 cm 633.18 633.18 RICE FISH CULTURE PRODUCTION ECONOMICS NORTH SUMATRA. 4439 4439