Soils are composed of minerals, organic particles and pores (porosity) in between. The total porosity volume depends on the property of soil minerals and organic content. For example, clay soil has smaller but more numerous pores than a coarse soil. A coarse soil has bigger particles than a fine soil, but it has less porosity or overall pore space. Water can be held tighter in small pores than in large ones, so fine soils can hold much more water than coarse soils.

There are three distinctive status relations between soil water and air relation:

1.     Saturated Soil – all the soil porosity is filled 
    with water.

2.     Field capacity – The maximum amount of water soil can retain, after the excessive  water from saturated conditions has been drained by gravity.

3.     Wilting point - the amount of water in soil when a plant is unable to obtain   enough water to remain turgid.

Generally speaking, the relation between water and air at field capacity state is in favor to the plants. At a saturation point denitrification may take place (nitrogen loss as a gas) and the root system may be damaged due to lack of oxygen especially since temperature increases, and as water content declines beyond field capacity, the water availability for the plant gets reduces as well.

However, during the irrigation cycle, the soil, water and air content continuously change. During the water supply stage, water content in the soil is always higher than at field capacity and it takes a few hours up to a few days for the excessive water to drain and reach return to field capacity status. As from this stage up to the next water supply stage (new irrigation cycle) the water content in the soil is gradually declining due to evapo-transpiration (water loss due to plant water consumption or directly evaporation from soil surface). As higher the irrigation application rate will be and as heavier the soil, it will take longer time for the water to drain back to field capacity.

One of the advantages of drip irrigation methods is that the time it lasts from the end of the watering back to field capacity is the shortest. This situation can further be improved by dividing the duration of the irrigation application time into a longer period (instead of a consecutive water supply). In other words water supply takes place a few times during the day (pulses). It means that water supply lasts just a few minutes at a time, according to the irrigation rate. However, the shorter the duration of water supply is, the efficiency of the irrigation system declines, because it takes a long time to refill the drip irrigation system with water, compared to the duration of water supply at a time. And at the end of water supply, the water drains out of the irrigation system to a lower part of the field. Therefore as the duration of water supply decreases the efficiency of water supply will decline as well.

Plastro^ג has recently introduced a new drip irrigation technology to overcome these constraints. HydroPCND emitter is unique in: Non-drain type, flow pressure compensator and very low flow rate 1 – 2.3 l/h. The layout of such non drainage irrigation system with almost a continuous water supply (a few times a day) should take into account a different soil water distribution and a different root system pattern according to soil type and plant. Such irrigation systems are working successfully throughout the globe either in soil-less or soil media, especially in subsurface drip irrigation and for fruit trees production.

A continuous water supply, according to crop water requirement, may end up with high soil salinity, especially in a heavy soil with low water quality, and in a high evapo-transpiration area. Therefore, a good irrigation management practice is vital, and leaching the excess soil salinity practice is advisable.