Campbell Scientific Sentek TriSCAN® Manual v 1.2a - Manual (Page 30)

TriSCAN Manual Version 1.2a
Copyright © 1991 – 2004 Sentek Pty Ltd All rights reserved Page 23
Fertilizer management
In order to ensure that no nutrients are deficient, fertilizer applications are normally based on soil and/or leaf
sample analyses. The degree of precision varies from a rough averaging approach, to precision farming
where sample points are matched to requirements using satellite tracking technology. Healthy crops require
more water and have different nutrient dynamics to crops that have been stunted or diseased through
inefficient fertilizer management.
Pest/disease management
Good pest/disease management keeps the crop protected and in good health, sustaining its potential growth
and transpiration rates. Infestations can result in lower than normal water and nutrient uptake.
Irrigation System
Variations in irrigation system pressure, flow and water distribution uniformity cause variations in irrigation
application. This affects root zone wetting patterns and therefore crop water use.
The preceding crop water use factors should be taken into account when matching your irrigations to areas
of similar crop water use. These areas are then represented by soil water monitoring sites and the data
collected at these sites is used for irrigation scheduling purposes.
Water Quality
The source and constituents of irrigation water, impact on osmotic potential (and hence plant water uptake).
Measured volumetric ion content (VIC), will increase with increasing irrigation water electrical conductivity
(EC). Water quality can vary both within and between seasons and between water sources.
A general view of macro scale zone selection
Macro zone selection is used to identify the total number of required zones and their locations on your farm.
A macro zone comprises areas of similar crop water use and fertilizer requirements.The aim of good site
selection is to select a monitoring site that reflects representative changes in soil water content, fertilizer
mineralization and crop water / fertilizer use trends.
The representative data gained from monitoring sites is used to schedule irrigations over a larger defined
area. This area (or macro zone) may be an entire field, or a sub-section of a field, where irrigation is applied
during a watering shift or fertilizer application.
As an irrigator, you want to replenish the soil water used by plants for growth and transpiration, whilst
maintaining nutrients at a level sufficient to ensure growth, but not too high so as to cause leaching losses. It
is important to understand the many factors affecting crop water use or transpiration and how these factors
may vary on your property.
A primary goal of good irrigation management is to match irrigations to areas with similar crop water use,
within the limits of your irrigation system flexibility. This consideration will ultimately determine how many
monitoring sites you will need and where you should locate them. The diagrams on the following pages
show how ‘factors that affect crop water use’ can be used to determine macro zones.
Firstly the topography must be considered,