Abstract
Subsurface drainage is a prerequisite to grow winter crops in the consolidated paddy fields in Northern Iran. A four-year study (2011–2015) was conducted to quantify the effects of subsurface drainage on the saturated hydraulic conductivity, water table, drain discharge and winter crop yields. Subsurface drainage systems with two drain depths of 0.65 and 0.90 m and two drain spacings of 15 and 30 m were installed at the consolidated paddy fields of Sari Agricultural Sciences and Natural Resources University, Iran. During four successive winter seasons, the water table depth and drain discharge were measured daily. Soil saturated hydraulic conductivity was measured twice; before drainage system installation and four years following the installation. Canola grain yields were determined at harvest of each cultivation season. During the study period, the soil saturated hydraulic conductivity increased with the highest increase in the top 0–30 cm. The deeper drains were more effective in controlling the water table compared to the shallow, and the daily drain discharge of the deeper drains in the fourth year were higher than those of shallow drains. The canola grain yield of all drainage systems increased significantly by the seasons, and the largest difference in canola grain yield between first and fourth seasons was 2191 kg·ha−1 (318% increase) in the fields with 0.90 m drain depth and 30 m drain spacing. Totally, it became clear that installation of subsurface drainage systems with 0.90 m depth and 30 m spacing in the paddy fields of Northern Iran can be recommended to achieve high yield of winter crop, soil condition improvement, and multi-purpose land use.
Highlights
The main reasons for the installation of subsurface drainage in paddy fields are to improve the soil condition and create more conducive working conditions for the use of farm machinery, especially for large-scale paddy plot farming as well as non-rice crop farming on paddy fields [1]
A field experiment was conducted in Sciences and Natural Resources University (SANRU) paddy fields during the rainy seasons (October to May) of 2011 to 2015 to evaluate a suitable drainage system for improving soil hydraulic properties and grain yield of lowland paddy soil
The saturated hydraulic conductivity of the soil in all treatments increased, which resulted in improved water movement in soil and drain discharge rates
Summary
The main reasons for the installation of subsurface drainage in paddy fields are to improve the soil condition and create more conducive working conditions for the use of farm machinery, especially for large-scale paddy plot farming as well as non-rice crop farming on paddy fields [1]. Subsurface drainage improves the productivity of poorly-drained soils by lowering the water table, creating a deeper aerobic zone [2], enabling faster soil drying and improving the root zone soil layer condition [3] to activate functions of paddy roots This results in higher yields than before, when soil layer conditions were anaerobic [4], and provides feasibility of winter cropping. Considering that drainage at the Northern Iran paddy fields is in its infancy, research and development on different drainage system designs and new techniques to minimize cost of drainage are of great importance, which involves pilot studies For this purpose, Sari Agricultural Sciences and Natural Resources University (SANRU), as a pioneer center in this subject, has implemented a subsurface drainage pilot with different drain depths and spacings. A further aim of this study was to determine the effect of different drainage systems on increase in canola (Brassica napus) yield as the second cultivation in the study area
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