Understanding variation in Concord productivity using precision viticulture coupled with traditional berry sampling.

Introduction: Last week, Dr. Terry Bates presented maps that provided good side-by-side visual relationships in the patterns of collected data sets. This week, I am going to use data taken from the same vineyard to show how vineyard productivity (crop yield, sugar production) can be evaluated by analyzing the distribution of berry weight and maturity data across simple linear relationships between canopy and crop yield. Results: Figure 1 shows that canopy NDVI at veraison positively related to crop yield, and that greater soluble solids were observed in cases of smaller vines (lower NDVI) and crop yield relative to larger vines (high NDVI) and crop yield. In simple terms, Figure 1 shows that small vines had lower yields, but greater soluble solids. The units of soluble solids are a concentration (Brix). As such, soluble solids can be increased by factors other than greater net canopy photosynthesis, such as lower berry water status. While berry water status was not measured, berry weight was. Figure 2 shows the same linear relationship as in Fig. 1, but with berry weight data distributed across the linear relationship between NDVI and crop yield. When comparing Figures 1 and 2, it is seen that lower berry weights occurred when soluble solids were high, and vice-versa. This suggests that the increased soluble solids in the smaller vines was a function of concentration, and not necessarily due to greater carbon assimilation. Berry weight can be uncoupled from soluble solids through simple algebra; the result is the absolute amount of sugar produced per berry, which provides insight into canopy efficiency. Figure 3 shows the full story of how vine size related to productivity: the absolute sugar produced per berry was actually greater in the larger vines that had relatively greater berry weight and crop yield, but lower soluble solids.

Take home: Variation in vineyard productivity can be evaluated using sensor-derived data coupled with berry sampling. Because soluble solids can be affected by other factors than canopy size and health, its measurement alone may result in an erroneous diagnosis of vine productivity. In this brief case study, the absolute yield and sugar per berry in the large vines suggests that these vines have healthy canopies and are not over cropped. Conversely, the small vines likely have small, inefficient canopies that cannot bear as much fruit. Thus, as stated in last week’s post, management is most warranted at improving vine capacity in the smaller vines, perhaps by limiting competition for water and nutrient uptake.

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by Cain Hickey, Ph.D.