Biochar in viticulture - new results

In the last three years it has been clearly shown that biologically activated biochar does not only have positive impact on soil-plant systems in the tropics, but in all soil types and climatic zones [Crane Droescher [2011], Ogawa [2010], IBI [2011]). While biochar improves water availability for plants and microorganisms in dry or seasonally dry farming areas, it also plays a substantial role in high rainfall zones because it improves nutrient dynamics through prevention of nutrient leaching. Spectacular crop growth can be seen in extreme climates (tropical or semi-desert), partly due to biochar's buffering capacity leading to the compensation of strong limiting factors (water in semi-deserts, washed-out nutrients in the tropics) .

In temperate climates, however, the achievable increase in harvest is lower as there are no extremely limiting elements which have to be compensated. In addition, potential maximum growth of many plant species is easily reached in temperate zones through using good fertilizers and careful seed selection. Therefore the advantage of biochar application in temperate climates is less evident as crop growth but rather is seen as plant quality improvement through optimizing plant nutrition. The following criteria are paramount:

1. Increase of plant resistance and hence reduction of plant protection products
2. Stimulation of soil microbial activity and symbioses between plants and soil organisms
3. Reduction in fertilizer use by optimizing the supply of nutrients, limiting nutrient losses
4. Improvement of taste and nutrient content of the crop
5. Improvement of shelf life
6. Reduction of greenhouse gas emissions and groundwater pollution

Quality improvement through biochar in viticulture

The wine region is geographically the world's largest agriculture area where the quality of the crop in relation to income has the greatest impact on the profitability of a product. While harvests have to reach from 8 to12 tons per hectare in almost all sites, as prescribed by the enforcement authorities (e.g., AOC), liter prices vary between 0.50 € and 20 € depending on the quality. Although marketing and location of the vineyard play a major role in profitably , an improvement in grape quality can double the company's profit margin or even increase it by several times. For this reason, the use of biochar in viticulture is of special interest, and also explains why the implementation of biochar research in wine-growing now holds a clear leadership position in Europe. Biochar field trials were applied this year by more than 15 companies in all major wine regions in Europe on more than 15 hectares of land.

The first major field test was completed in 2007/8 at Delinat Institute, in Valais, Switzerland. Plant, soil and grape parameters are annually recorded and evaluated. The description of the experimental setup and the results from previous years can be found in last year's Ithaka article: Niggli C, Schmidt HP: Biochar in Vineyards (2010).

Data collection - Methods

A description of the methods regarding leaf N content, shoot diameter and the numbers of inflorescences are published in: Leguminosebegrünung im Weinberg [Niggli 2009]. Additional results are reported here:

Leaf analysis: 30 leaves from 30 vines were taken per sample. With it the second inflorescence of the opposite leaf (as seen from the fruiting branches) was taken. Sampling was undertaken on 30/08/2009.

Leaf analysis:Grape analysis: 400 berries per sample were taken. In each case, they were the second grape (as seen from the fruiting branches) from the central region of the grape. Four to six berries per vine were taken from each of 4-6 grapes (about 80 plants per sample) in the experimental plots M / G / K while 10 berries from 4-6 grapes (40 stocks in total ) were obtained in experimental plot C. The time of full maturity in the earliest plot (Cleg3) and time of sampling was on 18/10/2010.

Harvests: Selected (only perfect grapes) harvest of 20 stocks were weighed by harvest time in the plots/allotments.

Phenology: The softening/ripening of the berries ( =veraison?) started in the study area during the last week of August. Leaf-N data were recorded on 26/8 and leaf sampling was completed on 30/08.

Statistics: Shoot diameters and numbers of inflorescences were tested for normality using the Kolgomorov-Smirnov test. A two-sided t-test was performed when the assumption of a normal distribution was met.

The experiment was carried out in a conventionally managed plot with extremely eroded grounds. The experimental plot contains 4 treatment types:

1. spontaneous green cover without cuts (spo)
2. leguminous green cover without compost application (leg)
3. leguminous green cover with one-time compost application (leg / co)
4. leguminous green cover + compost + biochar (leg / co / bc)

The one-time compost application was equivalent to 40 m3/ha while the one-time biochar application corresponded to 10t/ha.

Results

Leaf nitrogen (optical)

The optical method shows that the biochar treatment (leg /co/bc) had the highest leaf nitrogen content and that treatment with only the green legumes (leg) had the lowest (Fig. 1). The standard errors in leg / co and leg / co / bc treatments were relatively large.

Mineral supply according to leaf analyses

In terms of major nutrients, the differences between leg / co and leg / co / bc treatments were within the range of 12% (N) to 23% (Mg) (Fig.2-3). The biochar treatment showed slightly higher values for phosphorus, whereas all other nutrients were in the optimum range [Vanek] [Fardossi]. The calcium content in the leaf was higher in the leg / co / bc treatment. If one is to conform to the optimal standards set by Spring [2003], the balance for magnesium and potassium does not look promising: there was an oversupply of magnesium in the leg / co treatment and an increased uptake of it in the leg / co / bc treatment. On the other hand, there was an undersupply in potassium in the leg / co / bc treatment and an even more severe undersupply in the leg / co treatment.

Trace elements in both treatments were in the normal range. Here the differences were in the range of 26% for Zn to 56% for Mn (relative to the lower value).

Growth potential

The mean shoot diameter was largest for treatment spo, but did not differ significantly from leg / co / bc (two-sided t-test) treatment. Both leg / co and leg treatments showed significantly lower shoot diameter than spo and leg / co / bc.

Inflorescences

The number of inflorescences was highest on treatment spo and was significantly higher than for the other treatments; leg / co and leg / co / bc did not differ significantly from each other.

Yield

Grape yield which can be vinified was highest in leg / co / bc treatment; about twice higher than in treatment spo and almost three times higher than leg / co.

Grape quality

The anthocyanin and acid contents showed the greatest differences among the treatments. The highest anthocyanin content was observed in the leg / co / bc while the least was in the spo treatment. The total acid and malic acid were much less in the biochar treatment; the highest level was recorded in spo, while the treatment leg / co shows intermediate values. The differences in the polyphenol and the potassium contents among the variants was less than 10%.

Discussion of results

There was continually pronounced drought stress symptoms in the vines in the experimental plots in low-rainfall summers (yellowing of the oldest leaves in parts of the plants). It is possible that the ground is not very deepand that there is some variation of the subsurface structure within the experimental area This wouldexplain the rather high variation in the results.

Leaf nitrogen

The very low values in the spo treatment are most likely due to the severely eroded soil and the lack of fertilization during the experimental period. The N-reserves from the fertilizers before the start of the experiment appear to have been already exhausted. In the treatment leg there was apparently a strong competitive factor in the third year after planting. The big difference among the treatments leg / co, leg / co / bc and other permanently green covered plots most likely lies in the shallow soil and therefore increased exposure and the lack of compost fertilizer. The good supply of nitrogen in the biochar-treated plot could be primarily due to the indirect effect on the green cover, and only secondarily due to the direct effect of biochar: the assumed increase in water storage capacity resulted generally in increased productivity of the green cover and the biological activity of the soil, which in turn resulted to better nutrient mineralization.

According to Kamm [2010] and Van Zwieten [2009], however, it can be assumed that nitrification in the soil was improved significantly due to biochar: less nitrogen loss through volatilization therefore making more nitrate present for plants in available form. Also ammonium and amino acids were fixed on the surfaces of the biochar due to the high cation exchange capacity, so that leaching was prevented or at least slowed down.

Leaf analysis

There were apparent contradictions with the spectral N indices found for the N contents of the leaves. The relative N content in the leg/co may be positively influenced by relatively low leaf calcium values compared with leg/co/bc . Moreover, considering the variations between leaves and vines the sample size of 30 was probably too small for comparisons between methods. This sample size should be increased by further analysis.

The higher levels of potassium, phosphorus and calcium in the leg / co / bc are most likely due to the increased content of these two elements in the biochar. The improved phosphorus availability is also due to the advantages brought by the biochar to the biomass turnover by the green cover. Legumes are relatively phosphorus-limited. This leads to increased mobilization and fixation at a sufficiently high soil activity and then re-mineralization of the element.

Growth potential

In the treatment spo, growth potential was weakly correlated with the measured leaf nitrogen values. The elements which are limiting for shoot growth are obviously still more readily available than nitrogen, which is more important for leaf growth and leaf metabolism. In the other treatments, the values correspond with the expectations derived from the leaf nitrogen values.

Inflorescence

The results suggest that in the spontaneous (very sparse) green cover control, spo treatment, the supply of the vine with the important elements for flowering during the required time was better than in the other treatments.

The number of inflorescences in the biochar-treatment, despite the higher K and P contents in the leaves,was not greater than leg / co. It is therefore likely that it is their availability during the critical phases for flowering which is more crucial and not their shortage. We suspect that the green cover in the experimental area may have acted as a K competitor.

Yield

The high harvest volumes for leg / co / bc compared to leg / co coincide with the balanced nutrient supply according to the leaf analysis, while the availability was due most likely to biochar's better water supply and the higher biomass available from the green, reactivated soil. The treatment spo lead to very good inflorescences despite a low harvest, due to fungal attacks (Oidium and Peronospora). This was consistent with the meta-analysis findings, which showed that a strategic use of green cover reduced disease pressure in most cases [Wing 2009]. This observation will be verified through systematic data collection next year.

Grape quality

The significantly better (but still low) K-supply in leg / co / bc as shown in the leaf analysis was not demonstrated by high levels in the grapes. All treatments had a high level of potassium .

The massive differences in acidity are difficult to explain. In the spo treatment, the strong Oidium -infestation and the significant N undersupply in the vines at the time of veraison may have slowed down the ripening process. Lower acid levels are desired for the produced Pinot Noir. However, it remains to be verified whether reduction in acid levels is a general trend in other wine/grape varieties and climates, which would then be undesirable.

The total N contents in the berries somehow correspond to the expectations, which can be derived from the leaf-nitrogen values. Interestingly, significantly more nitrogen in the form of amino acids, both absolute and relative to NH4+, was stored in the berries in the biochar-treatment. Higher N content in the form of amino acids is a quality parameter, which speaks for a higher resistance of grape to pathogens, and is also important for yeast nutrition during fermentation . The significant increase of amino-N in the berries confirms the results of the previous year's experiment.

The anthocyanins in the biochar treatment are significantly higher, corresponding to previous year's findings. The increase in anthocyanin content, both for color and flavor development of the Pinot Noir wine is of relevance for high quality evaluation. It may also explain the lower attacks by Oidium, Peronospora and Botrytis.

Conclusions

The 2010 data collected for the biochar experiment confirm the results of previous years and show that in most cases biochar has a significant influence on all parameters investigated. Due to the significantly improved grape health, higher anthocyanin, higher amino-N and lower acid value an improved wine quality can be expected in the biochar treatment. It confirms literature findings (Lehmann 2003) that biochar treatments shift plant nutrient uptake shifts to their particular optimum ranges. For some elements, this means an increasing uptake while for others a decrease .

Despite these clear positive trends, it is still too early to draw a generalization for use of biochar in viticulture . The influences of soil type, climate, grape variety, secondary vegetation and microbial colonization are too great to simply apply the same statements drawn from a specific terroir to other locations. For this reason, numerous large-scale field experiments in various wine regions with different grape varieties were carried out in the spring of 2011. In all these cases, the same biochar in the same concentration (10t/ha) and activation method (see: Ways of making Terra Preta) was used. Data acquisition was performed by the same methods as in the above experiment. Reliable results can be obtained only from a series of experiments and on such basis it may then be possible to draw generalizations in viticulture.

Literature

Crane-Droesch A, Abiven S, Torn MS, Schmidt MW: A Meta-Analysis of Plant Biomass Response to Biochar, with Implications for Climate Change Mitigation via Biosequestration, submitted

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