Variable Rate Irrigation - Case Study 1, Greenvale Pastures

Background

Farm Area: 200ha
Irrigation Types: 1 x 580m Reinke Pivot, 2 x Big Guns
Current irrigated Area: 173.7ha
Irrigation Water Sources: Ashburton Lyndhurst Irrigation(ALIL) Shares & two bores

Date	1998	1998	2004	2005	2008	2011	2012
Event	Drilled for water and got it	Started spray irrigation with big guns	Put a pivot on to cover 84.5ha	Started using soil moisture probes for irrigation scheduling	Went to pressurised water with ALIL Stage #1	Started monitoring soil moisture variations across soil types	Put variable rate irrigation on Reinke Pivot

 
Electro Magnetic Survey Maps

 

 

 

 

 

 

 

 

 

 

Electro Magnetic (EM)Surveys are completed as the starting point for Variable Rate Irrigation (VRI) to determine how variable the soils are and where key features to be managed exist. Typically both EM layers surveyed (0-75cm & 0-150cm) show a similar trend, however both are taken into consideration when making management zones for irrigation purposes.

Zones for Variable Rate Irrigation

Greenvale Pastures has built its Variable Rate Irrigation (VRI) zones based off the 0-75cm EM map as the soil layer is the most variable on the farm. The EM survey map has been broken into five (5) zones and removed all the very small areas (<0.01ha) to create irrigation management zones for the pivot. From here these maps can be used in any VRI software and irrigation rates assigned to each zone. These then are uploaded to the VRI controller either via the internet or manually with a USB drive. The irrigation rate in each zone can be altered when needed by the user. It is recommended that the user have a soil moisture probe in each different soil zone to help fine tune the soil moisture management and knowledge of each soil class, particularly for the first few years of VRI operation.

Below, the EM38 Conductivity 0 to 75cm Zones map are the zones built based on the different EM conductivity across the surveyed site. The darker blue the area the greater its ability to store water, while the red areas have a lower ability to store water and thus a lower available water content. The map in the blue shows the actual irrigation application rates as a VRI map. The darker blue areas have a higher irrigation rate compared to the lighter blue areas which are the higher EM areas with greater water-holding capacity.

 

Overwatering = Yield Loss

In the 2011/12 season Greenvale Pastures put six soil moisture probes (neutron probes) across six different soils within the one paddock. The paddock was in wheat in the 2011/12 season and weekly soil moisture probe readings were being taken with the average of all six used for irrigation scheduling in the paddock. After completing the season and yield mapping it was realised that the wheat yield was suppressed considerably in what should have been the better yielding parts of the field.

 

 

 

 

 

 

 

 

 

 

 

	Full Point (mm)	Stress Point (mm)	2011/2012 Wheat Yield (t/ha)
Site 1	187	139.5	17.56
Site 2	233	178	12.31
Site 3	288	178	13.26
Site 4	232	178	15.58
Site 5	181	134	16.48
Site 6	106	70	10.00

With uniform irrigation it would have been expected that Site 2 & 3 would have yielded the highest due to having the heaviest soil. However, this was not the case. Both Site 2 & 3 suffered yield suppression compared to sites 1, 4 & 5. Over the 8.4ha that zone 2 & 3 covered there was an average yield penalty of 2.66t/ha from overwatering compared to zone 4. With wheat valued at $400/t this equates to $1064/ha in lost profit in these zones or $425/ha when averaged across the whole field. If the same comparison was done using an average of Site 1 & 5 this would equate to a lost yield of 3.71t/ha or $593/ha averaged across the whole field. These losses are significant and make a big dent in bottom line profit. If a VRI machine is worth $60,000 and irrigates 100ha it would cost $600/ha to install. By reducing the average yield loss (due to overwatering) of $593/ha across the whole field the VRI would be almost paid for in one year by irrigating each soil type to maximise yield production.

VRI Paid for in Year #1

Water Savings and Economic Analysis

Currently, after installing VRI on the pivot in November 2012 Greenvale is saving between 25-50% of the water per application by differentially applying the water based on soil type variations broken into five (5) zones on its application map.

This water saved equates to 12 litres per second on average, which would be enough of a water saving to run the additional water through a lateral that they plan to put on the remaining part of the farm to replace the big guns. If this water had not been saved Greenvale would have had to buy an additional 100 Ashburton Lyndhurst shares to get full water allocation for the farm. These shares, at approximately $6000/ha would equate to about $300,000 spent on irrigation shares to enable effective spray irrigation to be installed.

Greenvale Pastures’ investment in VRI & EM Surveying will not only enable maximised production in all areas of its fields for the 2012 season, it has also proved to be well worth the $66,000 investment (for VRI and EM Surveying), saving $300,000 on irrigation shares. That’s a whopping 454% return on investment in year one, without taking into consideration the yield increases!! There aren’t many other pieces of agricultural equipment that would give that big a return on investment!

454% Return on Investment

Summary

- The benefits to be had from EM Surveying and installing VRI are huge!
- EM surveying is the key to making the most of your VRI investment and managing your fields in a site-specific manner
- Detailed soil moisture monitoring is needed to ensure that each soil zone is not going over its full point or under its stress point and each rainfall event is captured. 
- Better management of nutrients in field, increasing nutrient efficiency and reducing the environmental implications of leaching and water quality
- It can be a powerful tool for managing the compliance constraints within your water consent

 

 

 

Disclaimer: The examples of Precision Agriculture in Action listed on this web page have been supplied to PAANZ by the organisations shown in each case. PAANZ has not verified them and makes no warranty (express or implied) nor assumes any legal liability or responsibility for the accuracy or use of the information contained within them.