G.H. Neilsen1,
E.J. Hogue1, J. Paul2, D. Neilsen1, B.
Zebarth3, N. Patni2, T.S.C. Li1,
M. Ihnat and A. Reynolds4
Agriculture and Agri-Food
Canada,
Pacific Agri-Food Research Centre,
1Summerland and 2Agassiz, British Columbia.
3Agriculture and Agri-Food Canada,
Fredericton
Research Centre, New Brunswick.
4Brock University,
St. Catharines, Ontario.
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ABSTRACT
An early phase (1993-95)
of this research involved field trials which demonstrated
a potential for effective use of various composts to improve the growth
of annual vegetable crops while enhancing soil quality. Subsequently, field
trials were established to test the effectiveness of various composts in
a range of perennial cropping Systems including vineyards, ginseng gardens,
specialty horticultural crop plantings including Echinacea as well as high
density apple orchards. Preliminary results from these trials indicate potentials
and limitations of compost use in horticultural production systems. This
research is still in progress. Research is also underway to optimize the
composting process to produce effective products from locally available
organics including wood waste and animal manures and inorganics such as
zeolites.
At the same time, large and increasing volumes of composted agricultural/ municipal/other organics are being generated which have the potential to improve the quality of these soils for horticultural production. Large volumes of compostable materials are produced from manures, generated especially from the high animal densities in south coastal British Columbia, from forestry waste including bark, needles and small branches which increasingly cannot be burned, and from municipal wastes including biosolids whose increased quantities parallel increases in population.
The increasing supply
of potential organic amendments being produced will result in an oversupply
unless large markets can be established. It is for this reason that a series
of field trials have been established on a range of horticultural crops
to assess the utilization of organic composts in horticultural production
systems. At the same time, research is under way to optimize the composting
process for manure and waste wood based composts suitable for horticultural
use.
A: Compost Utilization
1.Vegetable Crops. From 1993-1996, a randomized, replicated field trial was run to evaluate the use of various wastes as soil amendments for the production of carrot and chard on irrigated sandy soils. The scientific methods and experimental design are described in detail in a recently published manuscript (Neilsen et al., 1998). Some of the essential conclusions are reiterated here. In general, cumulative three-year yield was low for check plots receiving recommended rates of NPK-fertilizer. Treatments involving annual applications of 45 mT/ha of various organic wastes in addition to NPK-fertilizer usually had significantly (p=0.05) greater yield after application of Greater Vancouver Regional District (GVRD)-biosolids and Biowastes from Aldergrove (Table 1). Nutrient and metal uptake varied with amendment treatment and crop. Chard (Table 2) was affected more than carrots. The ability of organic amendments to augment plant N, as observed after application of GVRD-biosolids, may be the reason for improved yield of some treatments. Biosolids applications generally increased Zn and Cu concentrations in chard but not to toxic levels during the 3-year period. Properties of soils at the experimental site were affected by treatment in a relatively short time. For example, after 3 years of application of Aldergrove biowaste, soil chemical changes at 0-15 cm depth included increased P, Zn and pH relative to plots receiving fertilizer only (Table 3). At the same time, in these plots, soil physical changes after 4 years included approximate doubling of organic matter content, moderate increases in cation exchange capacity and slight increases in soil water holding capacity. Changes in water holding capacity were less than expected. Cu proved to be the most mobile of trace elements in the soil showing significant increases to the 15-30 cm depth (data not shown).
2. Organic Vineyards. In 1997 and 1998, 3 compost treatments have been applied in 2 different organic (no chemical use) vineyards. Treatments include no soil amendment (control) or application of 45 or 90 mT/ha/yr (dry weight basis) of organic compost as a surface mulch. The organic compost used in 1997 was Aldergrove Biowaste (ABW) whereas in 1998 application of composted dairy manure solids were applied as the appropriate treatment since ABW was not available in 1998.
Both vineyards have responded to the N contained in the compost. As illustrated by first year results from Harbecks vineyard, Pinot Blanc vines had increased leaf colour, petiole N concentration and yield with increased rate of compost application (Table 4). Grape quality was also influenced with increased juice soluble solids and titratable acidity at the highest rate of applied compost. The cumulative evidence indicated that inadequate N- nutrition is a major limitation to wine grape production in vineyards on coarse-textured soils where organic production regulations prevent the application of commercial fertilizers. Application of N-rich composts, as in these studies, is an effective method of improving growth and increasing yield of organically-grown wine grapes.
3. Ginseng. A study was initiated in 1996 to determine if application of organic compost could substitute for the traditional addition of straw in ginseng beds to prevent winter kill (Table 5). The proportion of ginseng plants surviving the winter of 1996-1997 after application of various combinations of compost and straw in 1996, however, was not significantly different among treatments with winter kill losses relatively high regardless of treatment. Leaf scorch symptoms, possibly indicative of salt stress, were however observed on plants in various compost treatments. The overall growth problems at this site prevented a definitive determination of the efficacy of compost as a straw-substitute in ginseng production. Initial results suggest that an effective compost for ginseng production should have a low salinity.
4. Echinacea. A preliminary 12-week greenhouse experiment with Echinacea purpurea indicated increased leaf growth of plants grown in sandy soils mixed with 10% by volume of BC-Pork and Aldergrove biowastes to which a standard fish fertilizer regime had also been applied (Table 6). As a consequence, a field trial is currently (1996-1998) underway to test growth of two Echinacea species ~urpurea and augustifolia) to applications of 0 (control), 25 and 50 mT/ha (wet weight) of Aldergrove biowaste applied in 1996 and 1997. The effects on harvest in 1998 will be assessed in this organic production system which also includes fertigation of fish fertilizer for 6 weeks each growing season.
5. Apple Orchards. Several trials are underway in high density apple orchards to assess the use of organic wastes as soil amendments or surface mulches. In one such trial, yield of 'Spartan' apple has been increased by various mulches including shredded paper mulch (Table 7). In contrast, periodic application of GVRD-biosolids (45 mT/ha in 1994 and 1997) have failed to increase fruit yield.Variable response has been observed from preplant amendment of sandy soil to 0.3 m depth with organic compost. In a randomized, replicated field experiment with 'Braeburn' apple on M.26 rootstock, planted in spring of 1998, all treatments involving application of 90 mT/ha of Ogogrow compost (produced by the City of Kelowna) prior to rototilling to 30 cm depth has significantly increased total shoot growth (Table 8). A similar experiment carried out with 'Gala' apple trees on M.9 rootstock in a commercial orchard has failed to result in significant growth responses after rototilling 3 different organic waste applications of 45 mT/ha to 0.3 m depth (data not shown).
B: Compost Optimization
In British Columbia, major sources of waste exist which may require some modification prior to their effective use in horticulture. Two such waste sources include manure from intensive dairy and poultry operations in the lower Fraser Valley and wood waste including ground bark, needles and fine branches from forestry operations throughout the province including that generated in the interior (e.g., Riverside Forest Products) where strict burning restrictions are in place. The intention with this research is to optimize the compost process with the objective of testing the horticultural performance of the compost material produced. The nature of this research is illustrated by preliminary research on poultry manure at Agassiz.
1.The Compost Windrows - Preparation and Operation. The material used for composting was essentially waste tall fescue grass and laying hen manure. About one part manure (by volume) was mixed with 3.5 parts of grass cuttings using a 'Bobcat' loader. Three trapezoid-shaped windrows, 9.75 m long and 1.2 m high, 3.05 m wide at the base and 1.62 m wide at the top, were assembled in a roofed shed with concrete floors. Two of the three windrows were passively aerated using nine 3.05 m long, 10.0 cm nominal diameter, open-ended perforated plastic pipes, laid 1.0 m apart at the base of each windrow. Two rows of 1.6 cm diameter perforations were drilled 12.5 cm apart down the length of the pipes, with the rows offset 90 degrees from each other. The pipes were placed with the perforations facing upwards. As the pile heated up, the warm air rose, which drew fresh air via the open ends and the perforations into the composting biomass. The two passively aerated windrows were laid on a 4 cm insulating base of wood shavings. After assembly, the windrows were covered with a 2.5 cm cover of wood shavings, also for insulation. The third windrow was similarly constructed but without the use of aeration pipes or insulation. A Sittler windrow turner was used three times per week to turn over the biomass.
The windrows were assembled on June 16, 1998, and were monitored for the next 114 days. A long-stem thermocouple thermometer was used to determine temperature of the composting biomass, about 50 cm below the surface, at three equally-spaced locations on the two long sides of the pile (total of six locations). Temperatures were usually measured five times a week, except on holidays.
On ten different days during the composting period, a composite of six representative samples of the composting biomass was collected from each windrow, for moisture content determination. Water was added to the windrows on two occasions, using soaker hoses, when the average temperature dropped to about 40 C in the windrows in order to stimulate microbial activity.
Results. All three windrows released some ammonia during the initial three weeks of operation. The passively aerated windrows had very little odour, whereas the turned windrow released malodours for several hours after turning, for about the initial eight weeks of operation. Figure 1 shows the change in average temperature of the biomass during composting. The mean coefficient of variation for temperature in the three windrows was less than 8 percent. The turned windrow consistently had higher temperatures than the passively aerated windrows during the initial eleven weeks of operation. More temperature peaks were observed in the turned windrow than in the passively aerated windrows, presumably in response to increased heat production by elevated microbial activity after turning. Figure 2 shqws changes in the moisture .content of the composting material which had 60% moisture initially. As one would expect, moisture content initially decreased much faster in the turned windrow than in the passively aerated windrow. However, after about 12 weeks of operation, the moisture content in all three windrows was similar.
All windrows shrank in size as composting progressed, but shrinkage was much greater in the turned windrow than in the passively aerated windrows. After 114 days of composting, the former had only 38% of the original volume compared to 67% for the latter. This suggests that much more organic matter is lost (presumably as CO2to the air) by windrow turning than by passive aeration.
Research is also underway at Summerland to determine the most effective way of composting wood waste using 4 concrete chambers constructed to allow active aeration of compostable substrate combinations of wood waste.
A series of trials are underway to utilize composted organic waste in horticultural production Systems. A 3-year trial has been completed which demonstrated successful use of several composts in carrot and chard production. Composts could alter plant nutrient levels and modify soil properties. It will be important to define what key soil properties need to be modified to optimize production of various crops but also to determine the implications of long term metal additions to soil, especially of Cu which tends to be high in local biosolids. There appears to be a role for high N composts in organic production of wine grapes and Echinacea where commercial N-fertilizers can not be applied. Defining and improving the N-mineralization capability of composts would be important for such organic growers. In contrast, preliminary trials with ginseng indicate this crop is sensitive to high salt levels. It remains to be determined if a low nutrient (low salt) compost could be designed as a replacement for straw in ginseng production. Results have been mixed in trials to assess the use of organic wastes in high density apple production. In some sites, growth improvements resulted after use of wastes as surface mulches or preplant rototilled soil amendments whereas no effects were observed at other sites. Future research needs to determine why these results are not consistent and also to assess long term effects in these perennial plantings.
Despite the efforts
described above, the number of compost products is increasing much more
rapidly than testing for horticultural use of materials. Inevitably this
will lead to market saturation with inadequately assessed compost products
and confusion of potential consumers unless compost producers interact with
compost users. It is for this reason that research is also underway to optimize
the compost process to design better compost products and to assess the
horticultural performance of these products.
LITERATURE CITED
Neilsen, G.H., E.J. Hogue, D. Neilsen and B.J. Zebarth. 1998. Evaluation of organic wastes as soil amendments for cultivation of carrot and chard on irrigated sandy soils. Can. J. Soil
Sci. 8:217-225.
Wittneben, U. 1986. Soils of the Okanagan and Similkameen Valleys. Ministry of the Environment, Technical Report 18; British Columbia Soil Survey, Report 52, Victoria, BC 229 pp.
