ghassem aghajani mazandarani
Abstract
Introduction: Better use of water and soil resources in paddy fields, increase in rice production and farmer's income, installation of subsurface drainage system is necessary. The main goalof these systems, are aeration conditions improvement prevention of water logging, yield increase, land use increase ...
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Introduction: Better use of water and soil resources in paddy fields, increase in rice production and farmer's income, installation of subsurface drainage system is necessary. The main goalof these systems, are aeration conditions improvement prevention of water logging, yield increase, land use increase and multiuse of the land. In different countries, installation of subsurface drainage cause yield increase and working condition on the land, but no research has been conducted in different depths and spacing. On the other hand, spacing and depth are the most important parameters in the installation of drainage systems, have a direct effect on incoming water into the drains. The aim of this research, is an investigation of the effect of subsurface drainage with different depths and spacing on discharge rate variation and water table fall, in order to analyze the improvement of water flow movement in the soil. Also, study the effect of different drainage systems on the increase of the canola yield as the second cultivation in these treatments have been compared.
Materials and Methods: To measure hydraulic conductivity in different depths, the auger holes have been dug (excavated). The saturated hydraulic conductivity in these holes wasdetermined using Ernst method (1950) before installation of drainage systems. In the drainage pilot plot of Sari Agricultural Sciences and Natural Resources University three subsurface drainage systems with mineral envelope have been installed. 1- The first one with the 0.9 m depth and 30 m spacing (D90 L30), 2- The second one with 0.65 m depth and 15 m spacing (D0.65 L15) and 3- The third one with 0.65 m depth and spacing (D0.65 L30) and one bi-level system with mineral envelope including four drains of 15 m spacing with 0.9 m and 0.65 m depths were installed alternatively. After auger hole equipment installations, in the middle spacing of two subsurface and water table reading possible, the water table fluctuation and drain outlet discharge rate from farm drains during canola growing season were measured on a daily basis. Also, canola yield during 4 years after drainage systems were monitored.
Results and Discution: The results showed that mean discharge rates of drainage systems have increased with time and in the fourth year it was better than first and second years. Duringthe second year, the highest discharge rate onthe first day was in the low depth treatment and after 3 days the discharge rates become the difference among less. In the third year, the discharge rates of high spacing drains (D0.65 L30) have become higher than of spacing drains (D0.65 L15) discharge rates. But, in the first day its discharge rate was less and one can conclude that it is due to horizontal flow. With passing time and soil structure improvement, one can observe better yield from drains with higher spacing (30 m) also. By performance of drainage and soil conditions improvement in the third and fourth year, the deeper drainage systems have becomes better and water table fall of deep drain discharge rate and soil condition improvement in these systems become higher. In bi-level drainage, by increasing deep percolation, the water table fall in this treatment increased with time. Also, based on monitoring water table, in the first and second years after 5th day and in the third and fourth years after 4th day the water tables of deep drains decreased to lower depth drains. Due to heavy soil in paddy fields and existence of hardpan, the performance of low depth drains in falling water table was better in the first years. With passing time and performance of drainage the conditions for water movement in the soil become better and performance of deep drainage systems improved and at the fourth year, deep drainage systems had better performance in draining water with respect to low depth drainage systems. Also, canola yield as second cultivation, has increased from first to fourth year and along with important of soil aeration conditions and performance of drainage systems, the grain yield hasincreased in different drainage treatments. The results showed a direct relationship between improvement of system performance and increase in grain yield. In the second year, grain yield increased in all treatments. On the other hand, the yield under drainage systems with deeper depth (D0.9 L30) even higher in the 2nd and 4th years than with low depth drain (D0.65 L30). This was because of more fall in water table levels during days after rainfall and also with next rainfall, saturation of soil up to surface layer in the plots with deeper drains were performed later and it may not reach up to thesoil surface.
Conclusion: Due to betterconditions of deep drains and with higher spacing in the improvement of paddy field use and also less environmental harm use of drains with higher spacing are recommended for these lands. On the other hand,a low increase in drain depth from 0.65 m to 0.9 m along with increase in spacing of30 m with respect to 15 m and even with 0.65 m depth, will have less cost. Due to decrease in the costs of drain installation with higher spacing, due to improvement of conditions, the performance of these systems in 2 to 3 years one can have cheaper drainage systems in the longest time and will improve the economic situation of farmers due to higher yield.
S. Hamzeh; AbdAli Naseri; H.A. Kashkuli
Abstract
Two issues of the drainage systems which are less studied in the literature are drainage in layered soils and bi-level derange systems. Hence, it is necessary to do more research in these topics. Therefore the present study was carried out under above conditions in the Imam Khomeini Farming and Industrial ...
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Two issues of the drainage systems which are less studied in the literature are drainage in layered soils and bi-level derange systems. Hence, it is necessary to do more research in these topics. Therefore the present study was carried out under above conditions in the Imam Khomeini Farming and Industrial Lands, located in the north of the Khuzestan province, Iran. In this area based on primary studies, lateral spacing was estimated about 70 m and they were installed at the depth of 2.1m. But after two years of establish these drainage systems, it was observed that due to existence a soil layer with a very low infiltration rate (less than 10 time in compare with its above and below layers) at the depth of 110 to 160 cm, drainage systems in 500ha of these fields had low performance. Then, in order to overcome with this problem, the implementation of bi-level drainage system was proposed. Hence, a new drain line was installed at the depth of 1.2m between the old drain lines. After establishment of these new drains one field was selected to evaluation the performance of this new system. In the selected field three rows of observation wells were installed (in total 20 observation wells). After equipment of these observation wells, water table fluctuation, inflow and outflow water values from the field were measured in 3 irrigation periods. Then the results of field observations were compared with the obtained results from analytical solution in the literature. Results show with establish new drain lines the problem of these fields are solved and the water table profile will drop-off to the below of root zone in less than 36hr. Also it was concluded that the rate of water table decline by moving from the end of field to the open collector of field will be increased and the discharge of deep drains are more than low-deep rains. Results show that analytical solution is not able to predict the water table profile with well accuracy and predicted values by this equation only in a small area of water table profile were consistent with the observed values in the field. The main reason of this difference was the specific situation of layers of the soil.
