We truly believe the secret behind the taste of wine, lies in the soil. It's hard to name a truly great Pinot Noir that doesn't come off limestone. Old soil maps helped us focus our hunt for the perfect limestone terroir. True Limestone derived soils in the Waipara Valley are considerably less common than one might think. This made our discovery of this site particularly exciting.
The slip that created our fan has mostly covered over the more common Awapuni soils (although they show up in patches on the western slopes and down in the paddock adjacent to SH1). Awapuni soils are easily recognizable as a very dark grey-brown silt loam; over increasingly massive and clayey olive-grey-orange silt-clay-loam that become rock hard when dry.
The rest of our fan's soils are derived from two types of limestone.
- Amuri/Amberley Limestone (the older of the two): a hard white fine-grained limestone (comprising calcareous mudstone and glaucontic siltstone) deposited in deep water starting around around 65.5million years ago.
- Weka Pass Stone/Omihi Limestone (younger): a hard, cream-coloured, massive, sandy limestone, with finely disseminated glauconite, laid down in shallower waters when the ocean receded starting around 34 million years ago.
The term glauconite refers to the blue-green sheen on these limestones. In North Canterbury, our glauconite is a friable greenish mineral containing the elements potassium and iron. The presence of glauconite tells us that these were certainly marine rather than freshwater deposits because the deposition of glauconite is influenced by the decaying process of organic matter degraded by bacteria in marine animal shells.
Potassium in these limestone clays has major implications for winemaking: it can influence the pH of the grapes, and makes determining the optimal time for harvest critical.
Looking along the Limestone ridge that runs parallel to and above the Golden Mile vineyards, it's possible to distinguish the segments of the hillside that have more limestone from those that have more glauconitic sandstone due to faulting. Our close neighbours on either side are under mainly glauconitic sandstone sections, while Fancrest Estate is formed mainly from a limestone section. Not far away, the glauconitic limestone reappears, and here, at the now abandoned Omihi Limeworks, it was quarried for some of the purest agricultural lime the South Island has ever produced. The works closed when the sandstone content of the lime made it uneconomical to quarry any longer.
Weathering and erosion of these two limestone types is what has built our vineyard soils, and is responsible for the dramatic changes in soil types across very small distances along this range of hills. It also explains the differences in the character of the Pinot Noirs from the different vineyards along the range.
The reason we were so excited about discovering this site, is that Rendzic soils are unmistakable: Rendzina is a dark, grayish-brown, humus-rich, intrazonal soil. Nothing else looks quite like it. On the crest of the fan above this and on the eastern foot of the fan, where the limestone is closer to the surface, the soils are almost black (the word melanic is used to decribe these Rendzinas).
Of all the soils, Rendzina is one of the most closely associated with the mother rock, and an excellent example of initial stages of soil development. It is usually formed by weathering of soft carbonate rocks like dolomite, limestone, marl, and chalk (mudstone). The name Rendzina derives from the Polish word "rzędzić", which means "to chat": Rendzina contains rocks which click and screech on the plough i.e., "talk" to the ploughman. The term now is used for a class of shallow soils over chalk, limestone, or extremely calcareous unconsolidated material in which the topsoil is calcareous. This makes for a very distinctive and interesting soil.
Both Weka Pass Stone/Omihi Limestone and Amuri/Amberley Limestone weather to create Rendzic Soils. Like all real Rendzinas, some of our soils directly over limestone have only an A horizon around 15-30cm deep directly over a marly limestone or mudstone C Horizon. Here the topsoil is thin: Base Saturation (BS) is 100% of which Calcium (Ca) 78%: Magnesium (Mg) 9.5%: Potassium (K)12%. Immediately beneath this, in the marl or mudstone, where the vines roots explore, the pH rises dramatically from around 6.6 to 8.1. It's Cation Exchange (CEC) is around 44.5 me/100g. Base Saturation of 100% in the ratio Ca 96%BS:Mg 3.3%BS:K 0.6%BS. This makes this soil perfect for growing Burgundian varieties.
These soils produce beautifully structured pinot with floral aromatics and a mineral seam that runs through the palate. The vines struggle to pull the minerals they need from these soil and we often have to foliar feed them with a cocktail of the minerals they are deficient in, mainly Iron and magnesium.
Moving just off the limestone marls and mudstones usually results in a gradual drop in alkalinity in the topsoil. In places however there is actually an increase in pH. These are the yellow-pale-orange areas on the vineyard map. pH 6.6-8.5; BS 95-100% of which around 70-90% is Calcium. These very dark grey-brown clay loam soils give our wines beautiful palate weight and lush aromatics. Viticulture on these particular soils is somewhat easier because there is less rocky material in the soil, but the young vines really struggle with the soil alkalinity.
The remainder of our soils are lighter and sandier and appear to be a mix of Glauconitic Limestone, Sandstone and the original Awapuni Soil. Generally they have a a lower pH than the Rendzic soils. Base Saturation 73-88% of which Calcium is 48-49%. Pinot Noir off these blocks are fine and aromatic and usually have bigger tannins.