Comparison of compaction and puddling as pre-planting soil preparation for mechanized rice transplanting in very gravelly Calcisols in central Iran

The conventional method of tillage and planting for rice (Oryza sativa L.) production in central Iran is wet tillage (puddling) and manual transplanting. In this region, four-wheel (two-wheel drive) tractors are commonly used as the power unit for the puddling operation. The sinkage of tractor wheels during the puddling may deepen the hardpan layer and would create problems if mechanical transplanting was adopted due to the difficulty of the traction wheels moving through the puddled soil. Due to the shortage of irrigation water and increasing labour cost in recent years, researchers are seeking alternative soil management that would reduce water requirement and facilitate mechanisation of rice transplanting. Two systems of soil preparation (compaction and puddling) were studied for possible utilisation with a two-wheel rice transplanter in a very gravelly clay loam soil (Typic Haplocalcids, USDA; Haplic Calcisols, FAO). Compaction was done with a tractor equipped with a 5 Mg roller, whilst a rotary tiller and a locally made rigid-tine field cultivator, named Khishchee, were used for puddling. ansplanter worked well following both compaction and puddling rice soil preparation treatments. However, wheel slippage of the transplanter following compaction was less than after puddling. Transplanting was more uniform and seedling establishment was high after the compaction treatment as compared to puddling. In the soil compaction treatment, paddy yield was higher and plant lodging was lower than after puddling. Soil compaction reduced both water requirement and growth period of rice. These results suggest that soil compaction is a practical and perhaps a better method for mechanized rice transplanting than puddling in very gravelly soils.