Development of In-Field Chipping and Shredding of Almond Prunings as an Alternative to Burning
Cooperators:
Objective: To determine the feasibility of in-field
chipping/shredding as an alternative to burning of almond prunings.
Introduction:
Almond orchards are typically pruned annually to maintain
tree vigor, prevent shading of interior wood, and maintain tree size. The brush is usually pushed out of the
orchard and burned. However, there are
increasing concerns about air quality and tighter regulations over agricultural
burning. Some almond growers are shredding the prunings in the field, but
foreign material on the orchard floor is collected with the nuts during
mechanical harvest, leading to problems at the huller. Excessive woody material is difficult to
separate from the hulls. Almond hulls
are sold to dairies as a feed supplement and excessive fiber reduces their
value. It is difficult and expensive to dispose of brush and other orchard
debris that has been separated from the nut delivery at the huller.
In 1996, a pilot test was established at Hopeton Farms in
Snelling using ‘Butte’ with solid-set sprinklers to develop shredding and chipping
techniques as an alternative to burning of almond prunings. The trial tested a Brush Bandit̉ chipper
and a Rears̉ shredder against the typical practice of pushing
the brush out of the orchard and burning it.
In 1997, a custom made, self-powered shredding machine by Bert Walters
was added to the trial. The trial is
being conducted in two blocks with different vegetation management strategies;
a planted legume mix cover crop which is mowed only after seed is set in May
verses the native vegetation with more frequent mowing. Prunings were chipped or shredded in the
falls of 1996-1998. Brush weights were
taken in 1997 and 1998. At harvest,
samples were collected from the windrows and the nut carts to calculate the
amount of pruning waste in each treatment.
Each treatment was processed separately by Lake Shelling and the final
hull products were again sampled. Final
hull products were submitted to an analytical lab in 1998 to determine total
crude fiber and acid digestible fiber content.
A second trial was established in 1998 at Green Valley
Ranch to test the number of passes with a Rears̉ shredder
required to reduce particle size to an acceptable level. This second trial is in a micro-sprinkler
irrigated Nonpareil:Carmel orchard. Harvest samples will be evaluated in this
orchard in 1999.
Results:
Chipping and shredding in 1997 resulted in a significant
increase in woody material in the finished hull product. In 1998 the woody residue levels in the
chipped and shredded areas were similar to levels in 1997 from the windrows and nut carts. However,
nut cart samples of woody material were much higher in 1998 than 1997 in areas
where brush was pushed out of the orchard and burned. The reason for this is unclear and lessened the differences
between treatments.
Hull
pile wood content was very low in the 1998 push and burn and in the
Walters treatments. Overall the wood in the hull piles was only 1/3 to ½ of the
amount in 1997. Wood content in the shredded and in the chipped treatments in
the native cover are low to moderate. Wood content in the shredded and in the
chipped treatments with planted legume cover are moderate, but lower than 1997.
Hull
pile fiber content was very similar for chipped, shredded, and burned
brush in 1998. The results were better
for all brush treatments in the native vegetation block than in the block with
a planted and late-mowed leguminous cover crop. This is probably due to the
more frequent mowing in the native block during the season resulting in
increased destruction of the woody material.
Conclusions:
Two years of data show that very small amounts of wood are
left in the hulls where brush is pushed and burned. However, one year of data
indicates that residues following treatment with the Bert Walters machine are
very similar to the residues from the push and burn treatment. Both chipping
and shredding with the standard shredder can leave objectionable residues in
the hulls, but the more frequent mowing in the native cover will reduce this
residue. Brush residue is pulverized with in-season mowing and increased
numbers of mowings results in less woody residue at harvest. This trial will continue for one more
year.
Table 1. Percent of wood fragments at several stages of harvest |
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WINDROWS |
NUT CARTS |
HULL PILES |
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Treatment |
1997 |
1998 |
1997 |
1998 |
1997 |
1998 |
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Burned-Planted Cover |
1.8% |
0.2% |
0.9% |
2.4% |
1.1% |
0.6% |
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Walters-Planted Cover |
- |
3.2% |
- |
1.0% |
- |
0.9% |
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Shredded-Planted Cover |
7.4% |
6.5% |
6.2% |
6.1% |
7.7% |
2.4% |
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Chipped-Planted Cover |
10.2% |
7.7% |
5.5% |
4.6% |
6.7% |
2.8% |
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Burned-Native Cover |
1.1% |
0.2% |
0.4% |
2.5% |
0.8% |
0.9% |
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Walters-Native Cover |
- |
0.8% |
- |
1.9% |
- |
0.8% |
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Shredded-Native Cover |
4.1% |
2.4% |
2.9% |
2.6% |
4.1% |
1.8% |
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Chipped-Native Cover |
6.7% |
3.6% |
4.7% |
3.0% |
6.3% |
1.7% |
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Table 2. Hull Fiber Summary by field |
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Planted Cover Crop |
Percentage Crude Fiber |
Percentage Acid Digestible Fiber |
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Burned |
26.8 |
40.6 |
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Walters shredder |
27.8 |
36.0 |
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Shredded by Rears |
24.9 |
37.6 |
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Chipped by Brush Bandit |
26.1 |
35.6 |
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Native Cover Crop |
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Burned |
22.1 |
31.1 |
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Walters shredder |
19.7 |
30.2 |
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Shredded by Rears |
20.9 |
29.5 |
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Chipped by Brush Bandit |
23.2 |
30.4 |
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