Fertilizer management – Campbell Scientific Sentek TriSCAN® Manual v 1.2a User Manual

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TriSCAN Manual Version 1.2a

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The crop does not respond to the extremes of low or high salinity in the rooting depth uniformly, but
integrates water availability, and takes water from wherever it is most readily available. Irrigation timing is
thus important in maintaining soil water availability. This reduces problems caused when the crop must draw
a significant portion of its water from the less available, highly saline soil water deeper in the root zone. For
good crop production, equal importance must be given to maintaining soil water availability and to leaching
accumulated salts from the rooting depth before the salt concentration exceeds the tolerance of the plant.

When the upper rooting depth is well supplied with water, salinity in the lower root zone becomes less
important. However, if periods between irrigations are extended and the crop must extract a significant
portion of its water from the lower depths, the deeper root zone salinity becomes important. In this case,
absorption and water movement towards the roots may not be fast enough to supply the crop, and severe
water stress results.

Leaching can be used as a management tool in controlling salinity in the crop root zone. However, this is
only effective when the drainage within and below the crop root zone is sufficient.

Salinity problems encountered in irrigated agriculture are very frequently associated with an uncontrolled
water table within one to two metres of the ground surface. In most soils with a shallow water table, saline
water rises into the active root zone by capillary action. Salinization from this source can be rapid in
irrigated areas in hot climates, where portions of the land remain fallow for extended periods. A good
irrigation management plan strives to apply sufficient water to meet the crop water demand plus the leaching
requirement.

Until now there has been no practical way to directly measure the degree of leaching achieved in a soil
profile. The traditional leaching requirement calculation is based on an estimate of the amount of irrigation
required to prevent excessive loss in crop yield caused by salinity build-up within the root zone.

TriSCAN offers the opportunity to directly track leaching of salts through the profile. From real-time
measurements of soil salinity and moisture, one can determine whether salinity is within acceptable limits for
crop production and whether leaching and drainage are adequate.

Fertilizer management

Fertilizers, manure and soil amendments include many soluble salts in high concentrations. Timing and
placement are therefore important, and unless properly applied, may contribute to environmental problems.
Proper timing, application and placement of fertilizer products can reduce nutrient and salinity movement
from the soil into waterways. At present, best practice in fertilizer application relies on regular soil and tissue
analysis to ensure that an adequate reserve of nutrients is available in the soil.

TriSCAN offers a practical means of tracking on a real-time basis where the applied fertilizer salts move
within the soil and the rate of plant uptake of these nutrients. While the TriSCAN sensor cannot determine
individual ion constituents, it can be used to optimize the timing of strategic soil sampling and so assist with
nutrient management. This has the dual impact of an economic benefit for the operator as well as a positive
environmental benefit to our waterways.