Polyhouse Saline Soil – prevention and cure
Many polyhouse/greenhouse growers see Saline soil problem. White grayish powder deposit on the sides of the beds and even on top of the soil is usual first visual manifestation of this. Indication of Saline Soil are also seen as falling production, stunting and die back of plants.
Definition of Saline Soil
There are many ways to define what is Saline Soil. One can define soil as saline when whitish crust is seen on top of the beds. One can also define it as when plants are not growing as expected and yield is down. A quantitative way to describe a soil as Saline Soil is when its E.C. is 4 ds/m or more. Some tests make it as 2 ds/m. The E.C. is measured by saturation soil extract method.
What make soils as Saline Soil
Soils become saline due principally to the irrigation water used and the fertigation methods. Different sources of irrigation water have different salinity as measured by T.D.S. or E.C. Most farmers using well water would have higher T.D.S. or E.C. and over time this would contribute to soils becoming saline.
The reason for Saline Soil is the accumulation of increased levels of nutrients and naturally occurring salts in irrigation water. All of these are not accumulated by the crop. The amount left over gets deposited in the soil beds. Growers rotate the same crop over a long period of time. Over years fertigation leaves sulfates and chlorides of sodium, calcium and magnesium. Over fertilization is the direct cause for saline soil.
Mechanism of Saline Soil
Fertigation followed with watering tends to make deposition of salts in layers. Salt accumulation makes it difficult for the plants to absorb moisture in beds. Generally near the top of the soil due to leeching of water, there would be less Saline soil. As the depth increases the Soil becomes more Saline. This is due to the fact that water in enough quantity does not leech through to deeper depths. Saline soil becomes compacted towards depth and this also prevents water leeching. Deeper salts travel to top and sides of beds due to capillary action, and are seen as white crust.
unabsorbed salts travel upwards due t capillary action
Measure Saline Soil E.C.
The preferred method is to have saturation soil extract. Mix soil sample in just sufficient water to get saturated paste. This method mimics the condition of soil at actual root zone of the crop. This takes some experience and time. Therefore some persons would take 1:1 or 1:2 ratio samples and try to extrapolate. However recommend saturation paste method.
Prevention of Saline Soil
The only way farmers can prevent is following two rules:
- Run enough irrigation water after every fertigation so as to cleans fully the drip lines as also to give enough water to leech salts to root zone and below.
- Give fertigation at levels just sufficient for vigorous growth of plants and fruits/flowers. Stay away from giving excess quantities to get more than optimum production.
Cure for Saline Soil
There are two ways to go for curing saline soil.
- Allow land to lie fallow and open to rain water. Or give excess irrigation water plus R.O. water.
- Adopt inter crop. Certain crops can assimilate water even when saline soils. Wheat, Barley, Mustard, Cotton, Spinach, Potatoes, Onion, cucumber, Tomatoes are some such crops.
More readings:
1. F&AO article on the subject
Would you, reader, like to share your experience with all of us? It would be knowledge gained.
Hi ; I have had opportunity to travel widely and have keen watched whatever farming practices the local farmers were engaged in. Back home been growing gerberas mostly in polyhouses, but outside in kitchen garden as well. i love these hardy perennials. good for business too if done in a routine orderly scientific manner. Also engaged in farming of wheat and organic vegetables on a small scale for me and family. My service profile has been that of an electronic and telecom engineer and now am engaged in web site creation and blogging.
It’s very helpful for all .tq for giving this worthy information.