Implementing Whole Farm Cycling of Nutrients and Carbon with Orchard Waste in Walnut & Cherry Production in Central Valley CA

RESEARCH Objectives Results

• (a) This project successfully developed a pilot compost program as specified in this objective. Design, implementation and product from a nutrient-cycled orchard waste compost derived from the waste of two fields (totaling about 40 acres) was completed. Through monitoring, the compost was found to meet the proper temperature and duration, though not even fully necessary as it did not contain raw manure. The final product was qualified as a high nutrient quality by Woods End Lab and PI spread it back on half of this acreage as a nutrient amendment and soil builder. 

The biodynamic ferment was used as an inoculant to enhance decomposition. The study did not quantify the effects, but daily monitoring noted that the sweeter smell was present in the days after, and the decomposition enhanced by observations in hand of smell and consistence. Further study is needed. However, biodynamic advising really came into the project through Blair’s guidance in building and approaching the processes in the pile as a kind of digestion of our orchard waste, optimizing the life naturally available on farm to recycle the nutrients. This can be seen further in her presentations with CAFF on YouTube. In developing this report Blair offered, “Properly made compost increases nutrient cycling by increasing enzymatic activity in the soil, increasing micro, nutrient, availability, and sequestering carbon.” And offers the studies cited below. 

Following this research objective, the project proved plausibility to incorporate both woody & green mass from orchard wood and cover crop waste back into a nutrient-cycled soil amendment. The success of this nutrient capture over-release is discussed further below.

Did we address the need to offer alternatives to burning orchard wood waste? The pilot demonstrates affirmatively an alternative practice to open-burning orchard material. The pros and cons of this alternative over other options need further research and discussion.

The project did offset nitrogen fertilizer inputs for half the acreage. The compost resulted in a good quality. Long-term analysis of this is not readily available in the scope of this project. It is also noteworthy to consider in any analysis that compost can replace but is not a fertilizer itself. Compost is known to add porosity to the soil, increase water-holding capacity, increase microbial life, and increase the humus content of the soil whereas inorganic fertilizers do not. By increasing the potential health of the soil in these ways, it increases the soil food and increases nutrient cycling further within the soil. Technical advisors Blair and Brinton affirm published studies and empirical on-farm experience which shows that the more self-sustaining and closed-cycle the nutrient process is, the less inputs are needed. 

• (b) How much of the original carbon did we capture? Initially, we aimed to capture at least 50%. To measure the actual outcome accurately required creating a "mass balance" structure, and this includes tracking volume change and ultimately dry weight change.

  Using the volume loss method (i.e. final volume divided into original volume) converted to weight (by taking account of moisture content) we estimated that we captured between 39% and 44% of the input carbon. To make this estimate more accurate, we used the quantitative carbon analysis from the start compared to the end, corrected for weight loss. This resulted in an estimate that was lower than we expected of 33% capture of total carbon.   The loss of pile volume method appeared proportional to the loss of carbon but it did under-estimate actual carbon losses. 

  As an explanatory remark, the fraction of input carbon not captured as final compost would have been biodegraded naturally during the composting process.  Mass burning would have lost all the carbon. However, composting is a "slow-burn" process (the compost heated itself to between 140 F and 150 F during the process). This heating speeds up the biological process of decay with the result that a considerable amount of carbon is lost in the atmosphere. This is to be considered biogenic CO2 - i.e. it does not contribute to global CO2 since it is part of nature's cycle).  The process also stabilizes a significant part of carbon as compost-humus. This humus will slowly continue to break down once applied to soil but it never completely disappears (as it does if the material is burned). The capture forces in the soil are strong enough to stabilize this carbon for long periods.

There is also a "margin of error" for our estimate of carbon capture. We estimated from the replicated carbon tests (5x) at the start and end of composting that the data variability was between 19 - 22%. For a field study, we believe this level of variance is not unusual but should be used to interpret the results with moderation.

• It was determined that we started with 396 cubic yards of compost and ended up with 179 cubic yards. The loss here is twofold: the increase in density reduces the apparent volume and the loss of organic matter by microbial decomposition reduces the mass. In the original 396 yards, we had 92.2 tons of total dry mass from the trees and cover crops, and after composting we recovered 75.5 tons. When we multiply this out by the respective start (32.2% ) and finish (13.1%) dry organic carbon content, the "mass balance" or recovery of carbon is as follows: start amount = 29.5 tons carbon; end amount = 9.9 tons carbon. Thus, if all the compost was spread over 20 acres,  that is approximately 0.5 tons or 1,000 lbs per acre of carbon added. Applying the variability estimate of 20% cited above, the amount of capture from composting chipped tree woods in combination with cover crops on this farm yields a range of soil-added carbon of 800 to 1200 lbs/acre.   This small quantity represents a potentially significant and measurable gain of carbon in the soil. 

We are satisfied with the result and consider that this was the first time PI was learning and making compost of this kind and in this way. It is possible that differing modes of management including the addition of water and frequency of turning could have influenced this capture upwards or downwards. 

• (c ) Did we demonstrate the plausibility of reducing non-organic fertilizer inputs through nutrient cycling into compost?  All the nutrients contained in the source ingredients except for potassium appeared to have been recaptured. Potassium declined most likely due to the moisture in the piles so it may only have been displaced downwards into the soil below the piles. Perhaps this potassium should still be considered part of the farm nutrient cycle, especially since all compost areas on a farm should normally be replanted to crops that will access any nutrients leached into the soil during composting.
  We also attempted to estimate nutrient recovery. At first we analyzed the chips and cover crop for minerals important for growing - P, K, Ca,Mg. This confirmed for example that the cover crops were very rich in these elements: P (0.7%); K (1.9%); Ca (3.1%) and Mg (0.2%). However, we cannot construct a mass balance since we do not know the dry weight proportion of cover crop mixed into the compost (same for the chipped wood). So we analyzed the fresh mix compost for these minerals and from this (using the model above) we were able to show that we started with the following total pounds of minerals in the compost:

  factor	Phosphorus	Potassium	Calcium	Magnesium
  START; pounds present in compost	184	1472	4232	331

   
  At the end, we repeated the analysis and then factored in the weight loss to arrive at the final collected pounds of minerals:

  factor	Phosphorus	Potassium	Calcium	Magnesium
  END; pounds recovered in compost	456	608	1500	304

  This data suggests we increased phosphorus and we lost potassium and calcium and stayed the same on magnesium. Since this is based on only one full set of tests on well-mixed initial material versus end material, more work (with replicated testing) would be required to obtain a better estimate (and to determine the margin of error for work like this).  For example, an increase in P suggests there may have been a transfer from larger inert particles into finer particles. To form lab tests, course, large fragments (> 3/8")  are excluded from samples. Potassium is considered very leachable in composts especially if piles are kept wet, and some of this (and calcium) may be found in the soil under the piles.  For example, early work on compost mass balance in Massachusetts by Brinton and Schonbeck found that many minerals in green waste compost leached into the soil over 8 months to a depth of over 2 feet. Studies in Germany with composting on biological farms have also shown considerable enrichment of soil by minerals under open-field composts.  In this project, we did not include enough analytical effort to sufficiently answer these questions with robust quantitation - it was felt that the appropriate level of lab effort to fully quantify these factors went beyond the scope of a practical field study of this nature. 
  As a final observation, the amount of minerals in these composts is returned to the soil. It has not been the practice of burning wood to gather ashes and return them to soils, although theoretically, this would have been possible; therefore this is a net recovery of the wood fraction of minerals captured in composting. Another observation is that accepted lab SOP's for compost analysis have the exclusion of "overs" (material not passing a 6 - 10mm sieve) as part of the analysis process. We recommend that a future study require the entire mass of compost and fragments minus foreign material to be repeatedly ground until fine enough to be included in the analysis. This would strengthen the data quality from analysis.

• (d) Did we improve nutrient utilization from orchard waste, cover crops, and other agricultural waste materials through composting? While a comprehensive analysis to determine if this method is "better" than others is challenging without comparative data, our findings indicate that the quality of the compost produced enhances soil health by maximizing the benefits of nutrients.  We appear to have gained phosphorus but as noted above, this would have to be investigated more. Our results suggest that composting could be more effective than burning wood and spreading the ash. We would have to conduct a direct study on this comparison to draw any further conclusions.

  It is also possible that incorporating green mass or cover crops into compost likely retains more nutrients compared to leaving them on the orchard floor to dry or tilling them into the soil. However, if leaching from compost has occurred this would not be the case. If the leaching happens in aisles between the trees, then the minerals could be recaptured by green manures.  An advantage of composting is that it concentrates and conserves nutrients, creating a clear and concentrated nutrient retention process.

• (e) Was this a cost-effective and beneficial solution? We learned a lot about the feasibility of a farmer designing, implementing, and gaining from a whole nutrient cycling compost program. It was well within plausibility and reasonability. However, the comparison suggestions below in recommendations would be very important to address if it is a recommendable best practice in terms of cost-effectiveness and beneficial solution. It is possible to calculate the entire costs of composting by accumulating various factors: machine time and fuel utilized; hours of labor by differing persons; and any supplemental materials used. In 2008 Brinton published a paper in Biocycle on how to calculate the "Energy Index" of composting which includes all machine time fossil fuel costs compared to the end value of the carbon.  In it, it was proposed that climate-smart composting would include the energy balance.  A study of this quantitative nature has not been performed in the scope of this project.