||The influence of tillage on rice grown on heavy Surinam clay soils was investigated in pot and field trials. Included were interactions with seed rate, nitrogen dressing and distribution, water management, and variety. Four procedures for tilled layer and seedbed preparation were studied morphologically, physically and chemically: wet, dry/wet, dry and zero.<p/>Differences between tillage treatments were found in sedimented layers, fragmentation, moisture contents, bulk density, dehydration curves, amount of moisture extracted by suction; permeability, moisture potentials, structural stability, content of extractable ammonium, and iron and potassium concentrations in soil moisture. Plant growth and grain yield were influenced by tillage through seedling establishment and growth, nitrogen mineralization in the soil, recovery of applied nitrogen in the rice plant, total amount of applied nitrogen and its distribution, surface drainage, and mutual shading.<p/>Shallow tillage, a few times in tilled layer preparation and a large wooden beam in seedbed preparation gave highest yields. The effect of the easiest procedures-- dry and dry/wet tillage--depended on the weather during the operation. The customary dry/wet tillage seemed harmful as it induced mutual shading thus reducing grain yield. Dry tillage was most beneficial to grain yield because of the high recovery of applied nitrogen. Wet tillage should be performed only when weather is unfavourable. Zero tillage is practicable, but weed control is troublesome.