Dear Nick
You will no doubt have heard that in Central Otago we had another severe air frost at the beginning of November, a bit like having a hundred year event 2 years in a row. I was actually in Brisbane but on returning home noticed that many of our trees were badly burnt even up to a height of 4 – 5 metres, and even in areas with good drainage were still burnt.

Once again I think the Rex’s took the brunt of the damage, and Heather North made a good observation that Rex’s, unlike a tree like Meyric, have little foliage which might give the buds some protection and therefore seem to get worse damage – another reason why Rex is not my favourite cultivar!. So we will have to wait and see what nut production is like – last harvest we had about 20 % of our normal harvest.
From my limited understanding of such events it does make any protection from frost extremely difficult.

On another tack I have just finished installing a couple of large Sand Filters for my irrigation – I got them second hand and cheap and they are excellent for removing the muck out of our water which comes from an open irrigation race.
I also got a 1000 litre tank cheaply and my mind has turned to installing a Fertigation System, so I am wondering has anyone else gone down this path, and if so what type of fertilizer would they use?

Now a cautionary tale, I have previously asked about applying Boron to help low levels, this year I did at around 100 gms per tree. I was a bit behind my program so I left some ewes & lambs in the orchard and was surprised when I looked back and found the old girls eating the grass where I had applied Boron. However since then we have had a series of unexplained ewe deaths [ no lambs ] – I asked help from the local vet who wasn’t aware of a problem with boron and even took some levels from the dead sheep. However in the light of such strong circumstantial evidence I have to say that the Boron probably was responsible for the fatalities, and you should not graze the land until a reasonable time for the mineral to work into the soil.

Compliments of the season to all, and I will ask Santa for a frost free year next year!
Jeffrey A Feint

Fertiliser

It would be good to hear how others deal with their walnut trees nutrition needs. Has anyone obtained any figures relating crop to nutrition levels? Does anyone do a nutrient budget; (comparing the nutrients exported as component of the crop compared with those imported as fertilizer and/or compost?)

We have had to take soil nutrient levels seriously here, because nothing grows unless we feed it. We classify our soil as ‘nutrient free’! Unfortunately, I neglected to have any soil samples taken when we moved on to the property and before I started throwing fertilizer around. However early readings of pH are 5.2 to 5.8, Olsen phosphate 20 ug/ml or so, potassium of .38 me/100g and Cation exchange capacity (CEC) of 10 to 16. In other words, fairly low, but not alarmingly so.

The reason I am discussing this is because at a recent fielday at Nick Empson’s walnut orchard, I said that I did not think that Nick’s entire sample of blighted walnuts from last year’s crop was actually a result of blight. I thought that Boron deficiency was in evidence too, and told my Franquette story. The nuts we were looking at were Serr, but they had the sort of damage that my Franquette nuts had in the first couple of years when they were coming out of their deficiency. At that point Peter Robinson, who works for JR Hill Laboratories where I get my soil and leaf samples analysed, said, “What do the soil samples show?” To which I replied, “Not as much as you would expect.”

And that is my problem. The plants are telling me a different story to the soil samples. That could be a consequence of the particular soil I am on, and the rock from which it is derived, but I suspect it is also partly due to the nature of the crop we are growing. Walnuts are big trees, even compared with apples, and most fertilizer applications go on tiny grasses, or very slightly bigger ones like maize.

I have noticed that a hungry walnut tree will not have a second flush of growth if you feed them in the summer, but if nutrient levels are already good in spring they will continue to grow until late summer. It is a bit like trying to get an ocean liner going compared to a rowboat. The leaves might change colour, but it takes a year or two for the tree as a whole to respond. So now I look for two things to assess nutrient levels in a walnut tree; leaf colour and leaf size. Look for nice green mature leaves and a certain amount of red in the new shoots. The terminal leaflet in the mature (compound) leaf needs to be at least as big as a man’s open hand.

Of course I still get soil and leaf analyses done. After 20 years of applying 1 ton of lime per acre, (The top dressing pilot feels comfortable with tons per acre) or about 0.4 tonne/ha, the soil pH rose to 6.6. That is quite high for many horticultural crops, but I have read that walnuts like a high pH, and the trees certainly look happy. The risk with a high pH is that other nutrients become unavailable to the plant. So I continue to put on 1 ton of lime per acre every year, and after another 10 years of doing that, the pH is still 6.6. Our soil is very acid and continues to neutralise the lime I put on year by year. Other people might get into trouble putting that much lime on their soil.

The following table gives our latest leaf analysis and compares it with one from California that was deemed to be “adequate”.

  Cheddar ValleyCalifornia
Nitrogen%3.32.8
Phosphorus%0.260.17
Potassium%2.41.45
Calcium%1.212.39
Magnesium%0.460.39
Ironmg/kg80 
Manganesemg/kg103 
Zincmg/kg2896
Coppermg/kg7 
Boronmg/kg10669

Without boring you with a blow-by-blow account of each nutrient, we come back to the discussion in Nick Empson’s walnut orchard. My soil sample shows Phosphate off the chart (high), pH on the high side though it does not seem to have affected plant uptake of the micronutrients, and Potassium low. And I never put on Potassium because I am on a soil derived from greywacke. I also had to admit that the mineral Borax I was putting on the soil seemed to be doing the job, whereas some people need to put on more complicated products or even spraying it on the leaves. (Hard to do on an 18 metre high walnut tree.) By the way Nick Empson’s walnut leaves looked spot on even though his orchard is organic. Waikato soil though.

I hope that helps someone. I watch for what the plants are telling me, but I also get soil and leaf analyses done, about once every 10 years.