Impact of rainwater harvesting systems on soil moisture changes of almond seedlings

Almost 6.1 billion ha (40%) of the earth's total land surface is dry. Moreover, nearly 5.2 billion hectares are Arid, Semi-Arid and Dry-Subhumid lands that are collectively referred to as drylands. It is estimated that 70% of partially productive drylands are threatened by various forms of degradation, impacting the wellbeing and future of one-sixth of the world population. The accelerated demand for rainwater can be met through the efficient rainwater conservation. In the world, about 73% of the cropland is rainfed. In such situations, rainwater conservation plays a greater role in maintaining and increasing crop productivity. In the rainfed areas, rainwater harvesting and management are assumed as the greater priorities. Water and soil conservation practices for agricultural lands includeinter-terrace rainwater conservation practices, conservation of rainwater at terrace level through bunds and guiding the excess runoff for safe disposal through grassed waterways to the farm ponds/tanks/dams for its storage and recycling to the agricultural lands. These are called hardware measures, which are of the permanent type provided for improvement of relief, physiography and drainage features. These are executed with major Government support with the purpose to check soil erosion, regulate overland flow and reduce peak flow. The present approach is to reduce runoff by adopting suitable management practices includeing, tillage practices comprising primary tillage operations i.e. summer or deep ploughing either every year or once in three years depending upon the soil type, land smoothening to avoid local depressions, frequent harrowing and secondary tillage practices with frequent inter-cultivations. Rainwater harvesting is a method of gathering and storing of rainwater. This method has been used to provide water for drinking, livestock, irrigation or refilling aquifers in a process called groundwater recharge. In some cases, rainwater may be the only available, or economical, water source.
Use of rainwater harvesting systems, with the goal of supply and increasing soil moisture is considered as a technique of soil and water management. In this study, to evaluate the performance of the systems, the variation of moisture in the soil profile of almond Seedlings irrigated with runoff was investigated in the Markazi province. The dryland and poor grassland are source of water erosion. In order to control the soil erosion and enhance of product, the seedling of fruiting trees was installed in stady parts of the watershed, in the southern slope with the slope of 17%. But the limiting factor was the soil moisture that with runoff collecting from precipitation could be provided. For this purpose, the rainwater harvesting system was used. Plastic lined farm ponds were particularly suitable for those areas where a large quantity of water was lost through seepage, especially where the soil was gravelly and porous. In earthen dams, there is also a common problem of seepage through the embankment. Under such circumstances, to check the seepage from all such types of farm ponds/ earthen dams, the plastic lining is a feasible solution. Polythene sheets of 200 microns were used as lining material for seepage control in the ponds. The sheets were spread at the bottom and on the upstream side, up to the top width of the pond. An average 10 cm thick soil layer also kept the sheet the sheet in proper place, to check external damage and to protect it from exposure to the sun. A permanent and most effective lining material is brick and cement masonry, but it is costlier than other lining materials. In this investigation, for each almond seedling, 40 cubic meter area was selected for collecting rainwater. In order to isolate and seperate the systems, sand filter in seedling hole was applied. The six treatment in the area were established consist of A: the current pasture-Tree hole filled with soil, B: the cleaned surface from bushes and rock-Tree holes filled with soil, C: The cleaned surface from bushes and rock-Tree holes filled with sand filter, D: The semi-isolated plastic and pasture-Tree holes filled with soil, E: The semi-isolated plastic and pasture-Tree hole with sand filter, F: The current pasture-Tree hole filled with super absorbent. In order to measure soil moisture for each treatment after each rainfall event in rain season (2013-2014), the calibrated gypsum block in depth of 30 and 60 cm were used. After each runoff, the data of measuring moisture dataset was read. Statistical tests were used in a completely randomized block design with three blocks (replication) each was composed of six treatments. Data analyses were performed based on descriptive statistics and ANOVA and Duncan tests.
According to the results, a significant difference was observed between the repetitions of each treatment. The soil moisture percentage between planting hole's treatments was with significant at 95 percent confidence level. But this percentage between depths of 30 and 60 cm hadn’t significant difference. The results showed the minimum and maximum of harvesting runoff and soil moisture percentages were in current rangeland and plastic semi-insolation systems, respectively. Also, results showed that the use of super-absorbent hole can increase soil moisture for seedling establishment and can be acceptable for the growth of dryland almond tree comparing to the current condition.