Note: When consulting, our time is purchased, and our view is that the client owns the work. In this case, the client gave us permission to share the report.
Note: The text below is from a report (“Initial Evaluation of ‘A Standardized Production Module for the Manufacture of Biodiesel in Asia & the Pacific’ ”) commissioned by a client.
If anyone wishes to see the whole report, please and request it.
The extracted section below regards expected output from a 600 ha plantation of Jatropha curas L., a plant that produces oil-bearing seeds. Our clients were considering investing in the plantation, which, the prospectus asserted, would provide 3,500 tones of biodiesel annually, and they hired us to determine the project feasibility and to determine whether and biogas could be made from seed cake, glycerol, trimmings and the like, and how much might be produced. We found that the stated yield figures were overly optimistic. (Please note that the footnotes, which work fine in a page-oriented medium, do not work as well on the web.) The section provided only concerns the issue of biodiesel yield. The full report covers other issues as well.
In order to estimate biodiesel yield from a Jatropha plantation, one must know a number of things, such as
Although listed first, we will discuss average yield last.
Unfortunately as mentioned above, there appears to be no scientific agreement as yet on which varieties may be higher yielding. The picture is further confused by the hype generated by commercial interests offering plants and seeds for plantations. (It could easily be, as well, that Jatropha does not bear true from seed, as apples do not.)
As regards the number of plants per acre, assuming that higher density always leads to a higher yield is obviously incorrect, since beyond some point, increasing that density increases stunting through resource competition or other factors. There appears to be some agreement that planting densities from 1,700 to 2,500 plants per acre[3] are optimal, and densities across that range appear to offer less variation in yield than one might expect, since those densities are close to the top of the yield per hectare curve, moving from plantings which are too sparse to those which are too dense.
As regards climate, the weather in Chennai offers sufficient rainfall (~1300 cm/yr) that on an average annual basis should be sufficient, given that it is widely reported that Jatropha can be grown in areas where rainfall is between 600 and 1500 cm/yr. Where the plants require it to become established, or if the soil does not store enough water to offer the plants sufficient moisture during the drier months, irrigation may be required. (The reviewed prospectus is silent on the question of any plans for irrigation.) There is some data[ref 18] that shows Jatropha prefers a higher elevation (and perhaps cooler temperatures?), but based on the resources available to us, Chennai appears to be relatively flat and low (~20–25 m).
The effect of agricultural practices on Jatropha yield is also rather uncertain, poorly reported and likely poorly studied. One report[4] indicates that the addition of fertilizers offers more luxuriant growth of branches and leaves, but no useful increase in yield of fruits or seeds. Experience indicates, however, that such growth is a characteristic of the overuse of chemical (NPK) fertilizers. The proper sustainable organic inputs such as compost may prove to be better at achieving more balanced growth and may therefore be more effective in increasing seed yield. In any case, where carbon credits are of interest, then the use of standard agricultural chemicals would no doubt negatively impact the carbon footprint of the project, and may therefore be economically counter-productive. Given that the effect of agricultural inputs will likely be highly site-specific (since local soil and climate may be quite different than the conditions studied elsewhere), further study of the effects of various inputs and the trade-offs involved should no doubt be an on-going aspect of the project.
Likewise, researchers are in essential agreement with regard to the percentage of oil in the Jatropha seed (35%–40%)[5] and there does not appear to be much near-term prospect for a Jatropha variety which has a rather higher oil content. Extraction through the use of a well-designed press of the proper capacity is sufficiently efficient (80–85%) that the addition of a solvent such as hexane is generally considered uneconomical. As well, conversion efficiency from Jatropha oil to biodiesel, where the process has been correctly done, is close to 100%.[6]
While good management would continue to pay attention to all such factors across the life of the project, for the purposes of initial yield estimates, it appears that the primary factors which offer the greatest uncertainty are variety, climate, agriculture, and ultimately per plant yield.
The first thing to mention with regard to per plant yield, as should be evident by now, is that reports for the yield of individual plants cannot be taken as predictive of the yield of their progeny nor of all plants surrounding them in a given plantation, particularly for a plant like Jatropha, which is essentially a wild plant with a very short history of intensive cultivation and breeding efforts. As mentioned, there may well be variations among these plants which breed true and offer higher yield— indeed there are both scientific efforts on-going to produce such varieties, and commercial outlets are presently selling seeds for which minor miracles are promised— but there are many barriers to gaining assurance that under the specific conditions which obtain for the Chennai project a reliable yield estimate can be assured.
The difficulty of obtaining reliable estimate is increased by the very wide variation in reported yield.
In the literature, the reports of yields vary greatly and are confusing.… [Thus] it is extremely difficult to determine what actual per hectare yield of nuts one can rely upon when growing Jatropha. Most figures cited were projections that often are inflated and over optimistic in order to procure funding for projects.[ref 4]
These variations may have a number of sources. Some are discussed in one of the best references available on Jatropha and biodiesel, Claims and Facts about Jatropha:
For reported yield values it is not often clear if values apply to fresh or dry weight (and how dry weight is expressed), and if the whole fruit… or the kernel alone is meant….
Seed yield can also be highly variable within plantation stands, varying for example from 0.2 to more than 2 kg per tree (Francis et al, 2005). This variability in yield is in contrast with the genetic variability, which is rather small in Indian germ plasm (Basha & Sujatha, 2007)….
The positive claims on J. curcas high oil yields seem to have emerged from incorrect combinations of unrelated observations, often based on measurements of singular and elderly J. curcas trees. Extrapolation of such measurements to larger areas with J. curcas monoculture crop (or even in intercropping systems), ignores the growth reduction in such systems occurring from the competition for natural resources, such as radiation, water and nutrients.[ref 13]
We note as well that it is not possible in any case to separate reported yield (whether per plant or per unit area), from the factors previously discussed, and therefore in a practical sense the reported per plant or average yield is in fact not a separate factor, but rather a summation of all the factors (previous to oil extraction) discussed above.
Note that in order for the projections in the prospectus— whether expressed in tonnage or as a function of ROI— each of the 600 hectares[7] will need to yield just less than 6 tonnes of Jatropha oil per year[8], which would offer ~3,500 tonnes of biodiesel annually. Most authors, however, report seed weight per hectare rather than oil or biodiesel volume per hectare. At 35% oil in the seeds, extracted at 80% efficiency, the necessary Jatropha oil will be produced by 21 tonnes of seeds per hectare.[9] (Alternatively, if we take it that the density of planting is 2,500 plants per hectare,[10] then to meet the projection each plant will need to produce 8.4 kg of seeds per year, on average.)
Thus annual yields will need to be 6 tonnes of oil or 21 tonnes of seeds per hectare, or about 8.4 kg of seeds per plant, to meet the stated projection.
As indicated above, the literature reports wide variations in either per plant or per area yield. Some reports offer rather conservative figures:
Jatropha yield [is] 1,000 kg seeds per hectare per year.[ref 10]
If results so far available from either the latest field trials of some research centers… and private companies… as well as the earlier experiences of a large number of Maharastra farmers with massive field plantations… the average yields from the currently available planting materials in drylands are unlikely to exceed… 1 t/ha/yr.[ref 20]
Of course, yields of 1 tonne of seeds per hectare per year would be less than 5% of the projected yield. Other reports are more optimistic:
5.60 lakh[11] ha. area will produce 6.00 lakh tonnes of Biodiesel…[ref 20] [~0.9 tonnes of oil per hectare per year, or 3.2 tonnes of seeds; 15% of projected yield]
Jatropha gives about 2 kg of seed per plant. In relatively poor soils such as in Kutch (Gujarat), the yields have been reported to be 1 kg per plant while in lateritic soils of Nashik (Maharashtra), the seed yields have been reported as 0.75–1.00 kg per plant. Thus the economic yield can be considered as 0.75–2.00 kg/plant and 4.00–6.00 tonnes per hectare per year depending on agro-climactic zone and agricultural practices. One hectare of plantation on average soil will give 1.6 tonnes oil [5.7 tonnes of seeds; 27% of projected yield]. Plantation on poorer soils will give 0.9 tonnes of oil per hectare.[ref 5]
One hectare of Jatropha curcas plantation on an average will produce 3.75 metric tonnes of seed yielding 1.2 metric tonnes of oil [32% oil, on an “extracted” basis].[ref 7]
From the experience in India and elsewhere, a plant density of 1,100 per hectare (spacing of 3x3 meters) has been found to be optimal…. In such plantations Jatropha gives about 2 kgs of seed per tree [24% of projected yield]. In relatively poor desert soils, such as in Kutch (Gujrat) the yields have been reported to be 1 kg per plant. The seed production in plantations varies between 2.5 tons[?]/hectare and 5 tons/hectare, depending upon whether the soils are poor or average.[ref 17] [0.7 to 1.4 tonnes of biodiesel per hectare per year; 12-24% of projected yield]
ICRISAT [International Crops Research Institute for the Semi-Arid Tropics] does not have any germ plasm that yields 7 [tonnes] of seed per hectare.[ref 5] [~2 tonnes biodiesel per hectare per year]
Gaydou, et. al. (cited by Duke[?]) gives a seed yield approaching 6–8 tonnes/ha with approximately 37% oil, and such yields could produce the equivalent of 2,100–2,800 liters [1.7–2.2 tonnes; 28-38% of projected yield][14] of fuel oil/ha.[ref 4]
The best of the yields presented thus far (immediately above) provides yield figures which are roughly a third of the yield target of ~6 tonnes biodiesel per hectare per year.
Some reports are even more optimistic than those above, but they appear for the most part to be simply passing along a figure presented in one study, which itself could easily have been an extrapolation from one mature tree:
[Jatropha] flowers in hot and rainy season and set fruits in winter. In field condition this may produce the seed yield as high as 12t/ha/year after five years of plantation (Jones and Miller, 1992)[15]…[ref 19]
Projections for more mature plantations lack a sound scientific basis, or worse, are based on wrong assumptions. Values from 0.4 to 12 t seeds ha-1 per year were projected for mature plantations (Jones & Miller, 1992), but no information on the background of this variation was given. A range of 0.5–12 t ha-1 (and [an average of] 5 t ha-1 as a reasonable estimate…) was reported without evidence (Francis et al, 2005; Daey Ouwens et al, 2007). Openshaw (2000) anticipated yields of 7.5 t fruits ha-1 y-1 (circa 5 t seed ha-1) for an established stand under good growth conditions with sufficient water, but without presenting the scientific basis.[ref 13] [5–7.5 t ha-1yr-1 seeds = 1.4–2.1 t ha-1yr-1 oil; 12 t ha-1yr-1 seeds = 3.4 t ha-1yr-1 oil; 56% of projected yield]
The summation appears to be provided by the previously mentioned Claims and Facts reference:
Predictions of [high] productivity, however, seem to ignore the results of plantations from the 1990s, most of which are abandoned now for reasons of lower productivity and/or higher labour costs than expected. Hence, a major constraint for the extended use of J. curcas seems to be the lack of knowledge on its potential yield under sub-optimal and marginal conditions.[16] This makes it difficult to predict yields from future plantations under sub-optimal growth conditions, the conditions where J. curcas is especially supposed to prove its value. Moreover, reliable predictions of the productivity are necessary to make reasonable decisions on investment… It has become clear that the positive claims on J. curcas are numerous, but that only few of them can be scientifically sustained. The claims that have led to the popularity of the crop, are based on the incorrect combination of positive characteristics, which are not necessarily present in all J. curcas accessions, and have certainly not been proven beyond doubt in combination with its oil production. (Jongschaap et al., 2007:4).[ref 13] [emphasis added]
We were unable to find any study, even the most optimistic, which offered a yield nearly as high as 21 tonnes of seed or 6 tonnes of oil per hectare per year, which of course would be required to meet the burden of 3,500 tonnes of biodiesel per annum. (Indeed, such yields may exceed the theoretical fixation rate for carbon via photosynthesis.) Our conclusion is that the projected yield is unrealistic and that the yield for a mature 600 hectare plantation— i.e. in 3–8 years— would, optimistically, be a third of that.
This of course also means that the amounts of material available to produce biogas are likely to be two-thirds less as well.
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