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Mark Krasnow
Dr. Stew Field, Karen Peterson, and I checked out the pits in the outgoing rootstock trial block yesterday. Unfortunately, but not surprisingly, there were huge soil variations down the rows the rootstocks were planted into, making comparisons between them much more challenging. These soils were formed from alluvial deposits by the Wairau river, which runs east/west. The rows in this vineyard run more or less north/south, cutting across the silt deposits laid down as the river changed its course over millennia.
If you look at the Landcare research soil maps, we see the major error made when this block was planted, possibly explaining why there has been little data of value derived from it over the thirty years it’s been in the ground. There are two soil types in the vineyard, and the rootstock bock, unfortunately, is planted across both of them. The ends of the rows are in a Hinds soil, which is silty and has no stones (blue in the image on the right). As you move down the row, the soil type changes to a Selwyn type (brown on the right), which is the more typical silt over stones alluvial soil in the wairau plains.
At one end of the trial, unfortunately the end that had the only 1103 Paulsen rootstocks, there was silt as far down as the pit went, approximately 1.5 meters. This is the Hinds soil. The next pit, only 9 bays away (approximately 60 meters) had about a meter of silt, with stones and sand underneath (into Selwyn soil now). The next pit down the row, only two bays (about 14 meters) down the row, had even less silt. The final pit, about 30 meters further down the row, only had about 50 cm of silt over stones/sand, and even had stones mixed into the thin silt layer.
Within the single Selwyn soil type, we can see the huge variations in the amount of silt over the stones, which leads to variable vine vigour down the row, illustrated by the NDVI image to the right. Evan had the trial only been planted only in the Selwyn soil, the large vigour differences due to the amount of silt as you move down the row could have easily swamped out any more minor rootstock effects. We did not see this trend in decreasing trunk weights as we moved down the row into the lower vigour soils, but this block would have been irrigated and fertilised for its entire life, a factor which could further obscure inherent differences in rootstock/soil effects.
Dr. Field’s more recently planted rootstock trial has corrected for this, with one set of reps in a uniform low vigour area of a single soil type as determined by NDVI mapping, and another set of replicates in a uniform higher vigour area of the same soil type. Stew’s trial is much more likely to show differences across rootstocks because he has corrected for the potentially huge soil variations across a block, and it has replicates in both high and low vigour soils, which can accentuate differences in growth, development, or ripening, due to rootstock. More rootstock trials need to be set up this way if we want to extract the most information from them.
Huge variations in vigour are very common in many vineyards in New Zealand, which are often located alongside rivers. This variability poses a challenge for vineyard managers, especially those farming grapes for red wine. For these growers, compromises must be made between managing the very vigourous vines in the silty areas and the less vigourous vines in soils with more stones. Our philosopohy at Thoughtful Viticulture is to differentially manage the vineyard to bring the vines closer to uniformity in growth and ripening. We wrote another blog about it, which you should check out if you’ve not seen it.
We will continue with our excavation of the roots from this trail block, but more as an observational and comparative exercise, since the soil based differences are so huge. We have pits in the same soil with some high/low vigour vines on either side (RG vs 8B), we have another pit in the same soil with a nematode resistant and vigourous rootstock (K51-32) across from the susceptible and low vigour 101-14. There looked to be some real differences in these side by side comparisons, which I will share in future posts or blogs, once we excavate more.
Onwards and downwards!
Have a wonderful holiday season, and we'll see you in the new year.
Kraz
Resources:
Landcare Research S Map portal
Information on the two types of soil
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