Category Archives: Irrigation

Irrigation demand: alike as two peas?

Article first published in The GROWER, December 2013

We tracked water use since planting in the first two crops of peas at the MicroFarm. We want to learn as much as we can about our soil and irrigation.

HydroServices’ Melanie Smith, our specialist support for soil moisture monitoring, established three neutron probe access tubes in each of our first two crops. These were read weekly and analysed to give a Paddock soil moisture content down to 80 cm.

Both pea crops were planted on the same day with the same drill. One had some nitrogen starter-fertiliser because our discussion group wondered if it would make a difference, but that is another story. For now, we are talking irrigation management.

We saw significantly different patterns from our two crops. Significant in that considering the usual 30 cm root depth, one crop needed irrigating a week before the other. Significant in that one would get through to harvest at the start of December without needing to be irrigated. The other would need irrigation. What was going on?

Let’s look at two graphs: Paddock 3a and Paddock 4a which are the two crops in question.

HydroServices_Block 3_Peas_2013-11-25  HydroServices_Block 4_Peas_2013-11-25

The top parts of these graphs show soil water content in the top 30 cm. We see that in each case the Full Point (116 mm) and Refill Point (82 mm) is the same. So we have 34 mm of readily available water our plants can access from the first 30 cm depth of soil.

The graphs show Paddock 4 reached Refill Point a whole week before Paddock 3. In fact, Paddock 4 hit Refill Point almost three weeks before Paddock 3, and but for a chance 12 mm rainfall would have gone into critical deficit in early November.

Let’s compare these graphs a bit more closely.

We see they tracked about the same to start with, then at the beginning of November Paddock 4 suddenly used significantly more water from the 0 ‑ 30 cm root zone than did Paddock 3. This is around the time the canopies reached full ground cover.

Our observations of the crops suggest Paddock 3 had more canopy so we thought it would be using more water than Paddock 4. Looking at the lower parts of Graphs 3a and 4a, we see that Paddock 3 used more water from deeper in the profile at 40 – 50 cm.

We did some Visual Soil Assessments and found more evidence of soil compaction in Paddock 4. Being the main gate access into the area it has seen more tractors, trucks and paddock forklift activity. So we expected to see compaction limiting root development.

Now lets look at the water content in the whole soil profile, right down to 80 cm, presumably well past any pea roots (Figures Paddock 3b and Paddock 4b).

HydroServices_Paddock 3_Peas_0-80_2013-12-03   HydroServices_Paddock 4_Peas_0-80_2013-12-03

The first thing to notice is much higher water storage, because 80 cm of soil has more readily available water than 30 cm of soil. So now Full Point is 314  mm and Refill Point is 232 mm giving 82 mm of readily available water for our crop to grow before we would need to irrigate.

When we compare these two graphs we get a different picture. Now we see the two crops using similar amounts of water through until 14 November. After that, Paddock 3 (the fuller canopy and better soil condition) used slightly more water than Paddock 4, and actually hit Refill Point a day or so earlier.

Overall, it seems our Paddock 3 crop is getting more water from deeper in the profile, accessing water from 50 ‑ 80 cm deep.

For a lower price crop like peas, reducing costs makes a big difference. Can avoiding compaction save the need to irrigate? 

How deep are your crops’ roots?

Open Day

The first MicroFarm Open Day was held on Thursday 5th December. The event received significant media coverage, including a two page spread in Rural News.

We are grateful for the excellent presentations made by our speakers, and for the quality of discussion that followed. Attendees travelled from South Canterbury, Manawatu and Gisborne to join local growers, contractors and their support industry colleagues.

Sarah Pethybridge’s presentation on Plant Growth Regulators helped understand this complex topic. The first demonstration results were being assessed, samples having been harvested the day before.

Programme

Short “theory” presentations in the Green Shed

  1. Why a MicroFarm; what we expect to learn – Dan Bloomer, LandWISE (and others)
  2. Soil nutrient picture; what we found, what we’ve done – Mark Redshaw, Ballance AgriNutrients
  3. Inoculants for legumes; our first trial and hopes – Weston Hazelwood, BASF Crop Protection
  4. Plant Growth Regulators; compressing pea flowering – Sarah Pethybridge, Plant & Food Research
  5. What the MicroFarm still needs – Dan Bloomer, LandWISE

Outside practical demos and discussions

  1. Buried drip for vegetables – Anthony Waites, ThinkWater
  2. Soil moisture monitoring; water use messages – Melanie Smith, HydroServices
  3. Soil compaction; penetrometers, VSA and a plan – James Powrie, Hawke’s Bay Regional Council
  4. Herbicide selection – Vaughan Redshaw, Fruitfed Supplies
  5. Plant Growth Regulator treatments; a first scoping study – Tim Robinson, Peracto

Download a printable pdf Open Day Programme here

The MicroFarm is a genuine community activity, as shown by the sponsors and supporters listed below. We are unsure of all the outcomes, but we know there will be much learning along the way.

SponsorsPanel

Buried Drip Irrigation Established

In April 2013, we established a buried drip irrigation system at CLAW in Block 2.

The installation was done by ThinkWater Hawke’s Bay using dripline was sponsored by Netafim and other materials by ThinkWater. Thanks in particular to Anthony Waites for all his efforts and care in getting the job one well.

Ground preparation began withHayden Greville spraying out the existing pasture.  Nicolle Contracting cross-ripped the area to 400mm then hoed the surface. This left a good surface and soiol conditions for the dripline laying rig.

The dripline is a 0.9mm wall thickness hose with 1 lph drippers at 400mm spacing was installed 762mm apart and 200+mm deep. This combination applies 3.2mm per hour using 4.16 lps on the half hectare block. That sits under our consent take rate limit of 4.8 lps, and applies a summer day’s water use in about an hour and a half.

While initial thoughts were for 400mm dripline spacing, we decided to try 762mm, or 30″ spacing to match the majority of process and other crops produced in Hawke’s Bay. The wide spacing will enable planting above a row of dripline which should be sufficient for row crops. It may prove to be a little too far apart for cereals or pasture  – time will tell. The block was set up as two halves, with control valves and sub-mains to fit. If we halve the dripline spacing (double the number of drip lines) we can split the application and still fit within the consent and our pumping limits.

Dripline installation was by ThinkWater and Nicolle Contracting using Trimble RTK-GPS auto-steer. We know exactly where it is! This should allow us to do deep cultivation such as inter-row ripping without damaging the dripline. The initial installation has not used a flushing sub-main. We wanted the system in and running for the  LandWISE field event and made do with individual dripline flushing. We will install the flushing sub-main; it is the only practical solution for a fully buried system like this.

System control is very simple. A battery powered clock sequencer controls two battery powered latching solenoid valves at field hydrant 2. The whole system in permanently pressurised so if the solenoid valves open, the pump will start up automatically. This suits us; it avoids electrically connecting the field valve station back to the pumpshed, and we only have one or two blocks to control. It is easy enough to set up and adjust as required.