Volume IV of a comprehensive study of Pakistan's irrigation system examines factors associated with low crop yields emphasizing farmers' perceptions of constraints. Farmers identified water problems as more constraining than all other farm problems combined. Reports findings regarding: (1) physical constraints; e.g., farm location, water availability and adequacy; (2) agronomic and economic constraints including use of fertilizer, selected farm technologies, high yielding crop varieties, and availability and sources of credit; (3) information constraints concerning crop selection, water application, soil-water-plant relationships, sources of watercourse conveyance losses, institutional services, and management practices; and (4) institutional and organizational constraints including the concept of collective goods and incentives to organize, organizational methods relating to mosques and schools, social conflict, distribution of power and influence. Appended are bibliographic references and a glossary of English (including local English) and Urdu/Punjab terms.