Maintenance Washing vs Leach Washing

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Raúl Bragado Alcaraz

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Published by: Jimena Blanco JascheckAgronomist on Greenkeepedia.com

Today's entry will discuss both techniques as mechanisms for controlling saline soils by means of salt washes.

Maintenance washing

It consists of maintain soluble salts present in the soil at acceptable levels that do not affect the development of the crop, slowly moving them to deeper areas of the soil outside the zone of root activity. To achieve this, it is essential to know the amount of water to apply in an irrigation. According to Robert N. Carrow & Ronny R. Duncan

CR= irrigation amount; ET= evapotranspiration; NL= flushing requirement (5-15%); CP= programme coefficient= irrigation system efficiency=1.1-1.3

According to Rhoades (1974), the washing requirement (NL) represents the minimum percentage of water that must pass through the root zone to maintain salts at an acceptable level for the crop.

The need for flushing is determined by the quality of the irrigation water and the salt tolerance of the crop.

washing_washing_needs — ECw: electrical conductivity of water; ECe: turf tolerance threshold; NL: flushing requirement; EC: electrical conductivity of water.

Let's see what a surface looks like before and after salt washing:

wash_Before — Surface salts BEFORE washing

salts after washing — Surface after washing

Leach washing

See is carried out when we start from an unacceptable level of salts in the soil for turfgrass development. It usually occurs in the following cases:

turf establishment
poor NL management (need for flushing) and/or CR (amount of irrigation)

Quantifying the phenomenon, in order to provide a solution to the problem, Rhoades and Loveday (1900) determine with the following formula the amount of water to be applied or depth of leaching:

leaching_water washing — Pw leaching water depth or amount of water applied; K factor that varies according to soil type and irrigation method; Ps depth of soil to be leached; CEe final desired soil salinity; CEeo initial soil salinity; CEw salinity of irrigation water.

According to Robert N. Carrow & Ronny R. Duncan (Best management practices for saline and sodic turfgrass soils 2012 ) the value of the K-factor varies depending on the type of soil and the way irrigation is applied:

Sprinkler irrigation in cycles or intervals: the soil is not in a saturated state and the time between irrigation cycles is 1-2 hrs in sandy soils and 2- 8 hrs in fine textured soils.

K=0.05 soils with more than 95% of sand

K=0.1 rest of soils

Continuous flood or sprinkler irrigation: the soil is in a saturated condition during the entire flushing.

K= 0,45 organic soils

K= 0,30 fine textured soils

K= 0,1 sandy soils

- In the event of rainfall

K= 0.05 fine rain

k= 0.1 heavy/torrential rainfall

Compared to other washing techniques, the leach washing has the following drawbacks:

more water that in maintenance washings
on growth of the plant is seen concerned due to excess salts
may require the machinery lockout by excessive humidity or flooding of the surface

How can I know the salinity level of my substrate?

We advise to carry out an analysis of saturated paste extract in the laboratory or purchase sensors for in-situ determination, e.g. the POGO sensor by @Tiloom.