Agriculture Reference
In-Depth Information
12.10.2 Drip Irrigation Water Quality Requirements
To meet the needs of agricultural irrigation and ensure national food security, drip
irrigation technology has been popularized and used in most of the areas in China.
Drip irrigation has various advantages such as water and energy conservation,
requirement of less time and labor, and prevention of plant diseases and insect
pests and has been adopted by many farmers. However, the drip irrigation system is
expensive and requires strict daily maintenance, especially the selection of water
source based on stringent standards.
Drip irrigation is an irrigation method carried out based on the crop water
requirement by using low-pressure pipe system and capillary emitter to add water
and necessary crop nutrients through uniform and slow drips into the crop root zone
soil. This method saves water; does not destroy soil structure; maintains suitable
level of water, fertilizer, gas, and heat in the internal soil for crop growth; decreases
evaporation loss; does not produce surface runoff; and almost does not cause any
deep percolation. The main characteristics of drip irrigation are as follows: (1) lim-
ited irrigation rate of only 2-12 L/h—the irrigation cycle is short, utilizing limited
water at frequent intervals—(2) low working pressure, (3) ability to accurately
control the amount of irrigation, (4) reduction of unnecessary evaporation, (5) no
wastage of water, and (6) control by automatic management.
However, the presence of high quantities of sediments, weeds, suspended solids,
and chemical precipitates in water may directly lead to clogging of the drip
irrigation pipe and dripper, and long-term accumulation may cause collapse of
the drip irrigation system, resulting in unnecessary economic losses. Similarly, very
high quantities of suspended solids in water may cause soil pore clogging, reduce
soil permeability, and make it difficult for the root system of the plants to get
sufficient oxygen, thus resulting in a slow plant growth. Hence, before being used in
the drip irrigation system, the water is usually filtered to ensure that it is clear. In
addition, application of drip irrigation to soil with high salt content or use of saline
water for drip irrigation may result in salt accumulation at the humid zone edge. If
this area encounters rain, then these salts may get washed into the crop root zone
causing salt damage and requiring drip irrigation to be carried out continuously.
Furthermore, drip irrigation, or drip irrigation with saline water, should not be
carried out in the absence of sufficient irrigation conditions, in places without
adequate rainfall, or in high-salinity soil.
12.11 Nanofiltration Technology and Its Development
Nanofiltration (NF) is a pressure-driven membrane separation process, whose
separation range lies between UF and RO. The membrane used for NF has a pore
size of a few nanometers, and a novel membrane developed for ultralow-pressure
RO separation technology is known as ultralow-pressure RO membrane. In general,
