Sahar Safaei - University of Tehran
Amir Sedaghatdoost - University of Tehran
Masoud Parsinejad - University of Tehran

Paddy fields' operations are often limited by adequate number of suitable days for farm machinery during either planting or harvesting periods especially in areas where farm machinery is often shared among several land owners. This study was conducted to evaluate the number of available days for farm machinery operation facilitated by surface drainage systems in paddy fields of Ghaemshahr, a humid region in Northern Iran. Rice is exclusively grown in the region, planted between 10 and 20 of April and harvested between 1 and 30 of August followed by canola or barely planting between 1 and 10 of September and harvested between 1 and 10 of April the following year. Soil physical and hydraulic properties were measured on 2000 × 2000 m grid lines. These measurements demonstrated high amount of clay and low hydraulic conductivity in the study area. DRAINMOD model was used to predict number of working days before and after improvement of existing drainage systems. The number of required working days was determined based on size of farm, speed and size of the machinery, and total area covered by each harvester. Drainage requirement were determined based on minimum dryness of surface soil for the harvester to perform satisfactorily. This value was set as 0.7 ?FC, in this study. Results show that, for existing drainage system, which consists of surface shallow ditches with 200 m spacing, the number of working days in about 33 percent of the region, does not satisfy the minimum requirement of working days (i.e. 10 days). Inadequate number of working days occurs in areas with high amount of clay and low hydraulic conductivity. Analyzing various scenarios using DRAINMOD, it is shown that reduction of drainage spacing by half, improves drainage conditions to offer adequate number of working days for the machinery during available harvesting period.

Surface drainage, Working days for machinery, DRAINMOD, paddy fields, Iran