Investigation of canola yield as a second crop in paddy fields under subsurface drainage

In order to provide feasibility of winter cropping in paddy fields, subsurface drainage systems should be installed to overcome waterlogging problems and to remove excess rainfall. In different countries, installation of subsurface drainage in paddy fields caused increases in yield and facilitated working conditions on the land. In Pakistan (Azhar et al., 2005) and India (Ritzema et al., 2008), the installation of subsurface drainage system resulted in increases in cotton, sugarcane, rice, and wheat yields. In a research (Carter and Camp, 1994), it was shown that subsurface drainage systems increased sugarcane yield. Totally, evaluation of influences of subsurface drainage systems showed positive effects on rice yields (Darzi et al., 2012; Mathew et al., 2001; Satyarayana and Bonestra, 2007), also it can provide possibility of second crop in paddy fields. Because of new installation of subsurface drainage systems in Northern Iran paddy fields, investigation of canola yield as a second crop has a great importance. By determining amount of yield improvement and harvested yield, farmers and government will have good point of view in future work.
In this study, the effect of three conventional subsurface drainage systems and a bi-level drainage system along with a control treatment on canola yield was investigated in paddy fields of Sari Agricultural Sciences and Natural Resources University. Experiments were done in randomized complete block design with 5 treatments in 2014-15. Water table depth were measured daily and in harvest time some of crop index like plant number in one square meter, pod number in plant, grain number in pod, 1000 grain weight and yield of canola were determined. Data were compared statistically by Combined ANOVA with least significant difference (LSD) test at the 0.05 probability level in SAS statistical software.
The results of statistical analysis showed that plant number, pod number, 1000 grain weight in subsurface drainage treatments were significantly more than control treatment. Also, the canola yield in subsurface drainage treatments were significantly 425 to 1025 kg ha-1 more than that in control treatment. However the rainfall during germination time was much, the drains worked well and water table was lower than 30 cm.
Improvement of aeration and quicker discharge of excess water in subsurface drainage treatments during canola growing season caused more canola yield. Generally, grain yield in drainage treatment with 0.9 m depth and 30 m spacing, Bi-level drainage treatment, drainage treatment with 0.65 m depth and 30 m spacing and drainage treatment with 0.65 m depth and 15 m spacing were 55, 35, 29 and 22 % more than that in control treatment. Due to these results and large areas of paddy fields in North of Iran, use of these areas during wet seasons for canola cultivation can be a helpful solution for producing oil grains and achieving to self-sufficiency.