Effect of wet land preparation period on weed density and grain yield of transplanted lowland rice.

Wet land preparation for rice production in the Philippines typically entails 21-30 d of several field operations that requires substantial amount of water. As irrigation water is getting scarce, there is a need to evaluate the effects of shortening the land preparation period on the grain yield and weed density of transplanted rice. We evaluated the effects of different land preparation period and manual soil leveling on the said parameters during the 2012 dry and wet season (DS and WS), and 2013 DS in Nueva Ecija, Philippines. Treatments were 1) land preparation period (7d, 14d, 21d), and 2) levelness of the soil (L1 = well-levelled and L2 = not-solevelled) based on the number of passes by a wooden plank during the final soil leveling. The shortest land preparation (7d) consistently showed the highest weed density among treatments but significant differences were only observed in 2012 DS and WS at 15 and 30 days after transplanting. The dominant weed flora were grasses such as Cyperus rotundus and Panicum repens. The L1 consistently exhibited grain yields that is higher by 3-13% compared to L2, but the difference was only significant in 2013 DS. We found no significant differences on the grain yield of rice among land preparation period but 14 d showed yields that is higher by 2-4% relative to other treatments. Our result indicates that shortening the conventional wet land preparation period (i.e. 21 d) did not affect the grain yield of rice. However, we recommend 14 d as optimum period of wet land preparation due to less weed density compared with 7 d.