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Summary:
This phase of the Truffle Orchard establishment has focused on: final pH adjustment of the soil; incorporation of a large amount of added organic matter; formation of raised beds; installation of an electric fence; simultaneous inoculation and planting of the first 128 (8 rows of 16) oak trees in December – January 2013; and arrangement for further soil amendment with agricultural grade gypsum (CaSO4).
Over the course of our project, new information led us to emphasize soil calcium (Ca) content over pH. This led to augmentation of soil organic matter level in order to raise soil CEC (cation exchange capacity), permitting our silty loam soil to retain more Ca while affording the benefits of organic matter for beneficial soil microfauna and microbial development.
Because our lime applications had already raised the soil pH to approximately 8.0, and because we would like to at least double the soil Ca level (to 3,000 ppm or more) over the course of the next two to three years, we will use agricultural gypsum (CaSO4) to accomplish this without further raising soil pH.
After having disked in the organic matter amendments, we borrowed a “rice levee plow” from the University of Missouri Horticulture and Agroforestry Research Center in New Franklin, MO, to construct 10 large East-West oriented raised beds spaced 5 meters apart on center. The beds are approximately 2 m wide and are raised roughly 30 cm above the inter-bed alleys which are roughly 2.5 m wide. The shoulders on the beds are approximately 0.25 m wide. Thus rows of trees are spaced 5 m apart. Along each row, the trees are spaced 3 m apart. The resulting 3 m x 5 m spacing provides a density of 667 trees per ha (about 270 trees per ac). This phase culminated in planting the oak trees, inoculating them with the Burgundy Truffle spores during planting, mulching the trees and protecting them from deer browsing with an electric deer fence and individual cylindrical wire mesh cages. Further soil amendments will be made as necessary depending on soil test results.
Introduction:
The adjustment of the soil properties has continued in Phase II and the main goal of soil pH has been reached, however the targeted soil organic matter and calcium levels are still in the process of being adjusted. The soil organic matter is still increasing as the various organic matter sources have been disked into the soil and break down over time. The calcium levels will be adjusted with the addition of gypsum just to beds after the trees have already been planted.
Project objectives:
We hoped to achieve a minimum calcium (Ca) concentration of 3,000 ppm at a pH of 7.5 - 8.0 throughout the upper 30 cm (1 ft) of soil. Recent work by Dr. Gerard Chevalier (retired, INRA, France) suggests that the soil Ca level is more important for truffle formation than is soil pH per se (which may be merely a common indicator of adequate Ca). By late August 2013, however, our soil pH had reached 8.3 with about half the desired Ca concentration. In retrospect, we see that the high silt content (and low organic matter and clay contents) of our soil limited our soil’s uptake of Ca. In order to augment the soil’s cation exchange capacity (CEC), and to provide the truffle fungus with a source of organic matter in its saprophytic phase, we applied and incorporated a large amount of organic matter (see below). As the organic matter decomposes and becomes incorporated into the soil, we will add about 10 tons of agricultural gypsum (CaSO4, approx. 21 % Ca) to add another 1600 ppm Ca to the upper 30 cm of soil.
Reaching the target of at least 10% soil organic matter was a challenge. Finding a readily available source of organic matter is critical from both a logistical and cost perspective.
Initially, 16 1,000 lb rolls of hay (old and musty) were rolled out over the orchard as evenly as possible and were disked in.
Another locally available source of organic matter was our spent shiitake logs, which had rotted outdoors for over 10 years. We rented a wood shredder and shredded two landscape dump truck loads of this material and disked it into the truffière soil as well. While it takes some time for this type of organic matter to decompose and contribute fully to soil CEC, the effect of these first two applications on soil organic matter content did not appear to be on track to become sufficient.
At this point, a large amount of organic material was needed to quickly boost the soil organic matter content (and to lower the soil pH a little), as the trees were scheduled to be planted in December 2013. We were able to track down a source of double-ground white oak bark mulch produced in nearby Salem, Missouri (distributed by Missouri Mulch). Fourteen loads of 14-16 CY of bark mulch were trucked in, spread evenly across the truffle orchard site and disked in thoroughly. We continue to monitor soil organic matter content, which seems to be rising significantly now. The organic matter content in May 2014 had increased to approx. 9% (from about 2% in August 2013), and this value does not include the bark mulch that remains to decompose in the soil.
3 - Calcium
The May 2014 soil tests also showed that soil pH has dropped to approximately 8.0 (from 8.3 in August 2013). The calcium levels however are now almost 1600 ppm (just over half of our minimum target level of 3000 ppm. We are currently evaluating sources of agricultural gypsum (CaSO4, 21% Ca) to further supplement the soil around the he trees themselves. We estimate that 10 tons of gypsum should provide an additional 1600 ppm to the upper 30 cm of soil. Because gypsum is considerably more soluble in water than is lime (calcium carbonate, Ca CO3), we will need to add gypsum gradually as the oak bark decomposes and gradually contributes to soil CEC. If the bark supplement and gypsum cause the pH to drop below 7.5, we will consider further boosting soil Ca content with lime.
