Two cells were buried in Mound 19 at Robin Hood Bay at 10 am 10 November 2000 and removed 10am 27 April 2001. That is, they were in the ground for 168 days. Each cell was placed 10 cm below the surface of the mound, one on the north side, and one on the south side. This configuration was used to see if there was any significant difference in the thermal environment as a result of solar energy absorption being greater on the north face.
Two cells were buried in mound 19 at Palliser Bay at 10 am 10 November 2000 and retrived 10 am 1 May 2001. As with Robin Hood bay, one cell was buried on the north side of the mound, and one on the south side. The period of burial was 172 days.
Two cells were also buried in a second mound at Palliser Bay in a similar manner to the first, but on a mound which had been mulched with a surface layer of stones. This was to see if the stones made any difference to the thermal environment in the mound.
The results obtained were as follows:
Cell Weight1 Weight2 Delta NDays DegC 1 11.64976 12.15820 0.50844 172 20.54 Whatarangi Mound 19 North 2 11.81279 12.30937 0.49658 172 20.14 Whatarangi Mound 19 South 3 11.80738 12.32275 0.51537 172 20.77 Whatarangi Stone Mound North 4 11.72338 12.27052 0.54714 172 21.80 Whatarangi Stone Mound South 5 11.71057 12.16097 0.45040 168 18.88 Robin Hood Bay Mound 19 North 6 11.84573 12.30704 0.46131 168 19.28 Robin Hood Bay Mound 19 SouthThe mound with the stone mulching has a mean temperature of 21.29 degrees C compared with the mound with no stone mulching of 20.34 degrees C. Thus, the surface stone mulching has increased the temperature by 0.95 degrees C.
Thus it can be seen that the Palliser Bay thermal environment is somewhat warmer than the mounds at Robin Hood Bay. The mean temperature at Robin Hood bay is 19.08 degrees C, compared with the un-mulched mound at Palliser Bay of 20.34 degrees C, a difference of 1.26 degrees C.
These differences may not appear to be very large, but it must be remembered that these values are integrated mean temperatures, and are quite significant.
In the 1999-2000 two root tubers were planted, one in the north side and one in the south side of each mound. The plants on the north side produced significantly greater yield. Since there is no clear pattern of difference in thermal soil environment, this increased yield is more likely due to greater exposure to sunlight for photosynthesis. The foliage of the north side plant shaded the south side plant.