Figure 8. Note 1 below. The picture is a condition of the land that is inundated or in other words land with poor drainage system. Land with poor drainage or flooded, generally can not be used as land to grow crops other than rice. Because the plants will die, where will the plant can not get oxygen for root respiration of plants, otherwise it will rot the roots of plants, and consequently the plant will die. So that the land can be planted the land drainage conditions must be improved.
Figure 19. Land with drainage Ugly
Drainage of agricultural land is defined as the creation and operation of a system in which the flow of water in the soil created such that both the depth of inundation and groundwater can be controlled so as to benefit the farming activities. Another definition, drainage of agricultural land is an attempt to remove excess water naturally or artificially from the ground or from the ground to avoid the adverse effects on plant growth.
On the undulating land drainage is more related to erosion control, while in the low land (even) more to do with production. The above objective is achieved through two kinds of direct influence and a large number of indirect influence. The direct effect is mainly determined by the hydrological conditions, the hydraulic characteristics of the soil, and the design of drainage systems, namely (1) a decrease in ground water level above or in the ground, (2) issued a number of water discharge from the drainage system.
Indirect influence is determined by climate, soil, plants, technical culture and social and environmental aspects. This indirect influence is divided into the influence of a positive result and that result in negative or dangerous. Indirect influence of drainage has a positive influence on crop is (1) or a salt leaching of hazardous substances from the soil profile, (2) Recovery of water drainage.
While the indirect influence that is negative is (1) the environmental damage in the downstream part because contaminated by salt, (2) disruption to the infrastructure for their channels.
The positive influence indirectly from decreased water level (1) enhance soil aeration, (2) improving soil structure, (3) improving the availability of nitrogen in the soil, (4) increase the variety of plants that can be grown, (5) adds to the ease of working tools and agricultural machinery, (6) enhances the soil’s capacity to store water.
While the indirect negative effects of decreased water level is (1) accelerate the decomposition of peat soil, (2) the reduction in the surface of the ground, (3) the oxidation of pyrite.