San Benito County Cover Crop Trials
Richard Smith
UCCE San Benito County, 649-A San Benito St., Hollister CA 95023-3952
1. WINTER COVER CROP TRIAL
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Trial Specifics |
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Cooperator: |
Wayne Shingai, Grower |
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Location: |
San Juan Bautista |
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Soil Type: |
Sorrento Silty Clay Loam |
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Planting & Irrigation Date: |
December 12, 1990 |
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Harvest Dates: |
March 8 and April 3, 1991: 86 and 112 days after seeding respectively (see below) |
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Harvest Method: |
One Meter2 was harvested from each plot |
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Plot Size: |
One 40-inch bed wide by 25 feet long |
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Plot Design: |
Randomized Complete Block Design |
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Treatments: |
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Plot |
Varieties |
Hole1 |
lbs/A Seed |
Configuration2 |
|
1 |
Lana Vetch |
22 |
71 |
3 |
|
2 |
Lana + Oats |
18 + 20 |
26 + 14 |
3 |
|
3 |
Oats |
26 (x2) |
43 |
3 |
|
4 |
Bells Beans |
36 |
105 |
3 |
|
5 |
Bells + Oats |
30 + 20 |
52 + 14 |
3 |
|
6 |
Phacelia |
10 |
8 |
3 |
|
7 |
White Senf |
10 |
12 |
3 |
|
8 |
Oil Seed Radish |
10 |
11 |
3 |
|
9 |
Phacelia |
10 |
2.7 |
1 |
|
10 |
Phacelia |
10 |
5.3 |
2 |
|
11 |
Phacelia |
10 |
8 |
3 |
|
12 |
White Senf |
10 |
4 |
1 |
|
13 |
White Senf |
10 |
8 |
2 |
|
14 |
White Senf |
10 |
12 |
3 |
|
15 |
Oil Seed Radish |
10 |
3.5 |
1 |
|
16 |
Oil Seed Radish |
10 |
7.0 |
2 |
|
17 |
Oil Seed Radish |
10 |
10.5 |
3 |
1 Hole size of Plant Jr.R Planter
2 Number of seed rows/bed
Results
This trial was conducted to compare the productivity of various cover crops at a December planting date. It should be mentioned that the cover crops experienced extremely cold temperatures (in the mid-teens) during the last week of December at which time the soil was frozen to a depth of three inches for over a week.
The data from Table 1 indicate that Lana vetch, which is normally a very productive variety for this area, was not extremely productive in this trial (0.73 tons of dry weight/A and only 59.0 lbs of nitrogen per acre in the tops) due to the cold weather and the short time the trial was conducted. It was not flowering at the time of harvest and if it was allowed to continue to grow during April and it would have been more productive. Oats were in the early boot stage at the time of harvest. The high concentration of nitrogen in the tops indicated that they were still in a very juvenile state and also would have been more productive if allowed to grow through April. Neither bell beans nor oil seed radish had good stands and this trial is probably not a good measure of their productivity. Phacelia was the most productive cover crop yielding 2.85 tons of dry matter per acre during 112 of the coldest days of the season. White senf was also extremely productive yielding 2.71 tons of dry matter per acre. Both varieties were able to accumulate large concentrations of nitrogen in the tops (218.1 and 219.3 lbs/A respectively), indicating that they both have good potential for reducing nitrate leaching. At the time of harvest the Phacelia was in the bud stage and the White Senf was in the early flower stage. Both of these varieties were extremely vigorous and rapidly covered the beds, offering good competition with weeds.
Table 2 indicates the effect of seeding rates and harvest dates on the productivity of Phacelia and White Senf. Both varieties grew dramatically from March 8th to April 3rd. In the case of Phacelia, increasing the seeding rate from 2.7 to 8.0 pounds of seed per acre greatly improved the dry weight production. Likewise, increasing the seeding rate of white Senf from 4.0 to 12.0 pounds of seed per acre greatly improved its productivity. The higher seeding rate also increased the nitrogen per acre found in the tops both of the these cover crops.
A simple analysis of the percent of the dry weight of Phacelia that
was made up of leaf tissue and that which was made up of stem tissue revealed
that an average of 51.3 percent of the plant is leaf tissue and 48.7 percent
is stem tissue. The nitrogen analysis of these tissues revealed that the
leaves were composed of 2.39 percent nitrogen and the stems were composed
of 4.12 percent nitrogen. This finding is surprising as leaf tissue is
generally higher in nitrogen. If this finding can be verified in future
studies it may help explain why the stems of Phacelia break down so rapidly
upon incorporation.
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Table 1. Biomass and nitrogen production of various cover crops harvested on April 3, 1991 (112 days after planting). |
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Variety |
Dry Weight T/A |
% Nitrogen of Tops |
Lbs/A N in the Tops |
|
Lana |
0.73 |
4.03 |
59.0 |
|
Lana+Oats |
1.02 |
4.00 |
79.1 |
|
Oats |
1.52 |
3.68 |
111.9 |
|
Bell Beans |
0.22 |
2.92 |
12.5 |
|
Bells+Oats |
1.21 |
4.00 |
97.5 |
|
Phacelia |
2.85 |
3.82 |
218.1 |
|
White Senf |
2.71 |
4.04 |
219.3 |
|
LSD(0.05) |
0.93 |
0.70 |
38.4 |
|
C.V. |
36.04 |
10.40 |
18.9 |
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Table 2. Biomass and N production data for various seeding rates and planting configurations of Phacelia and White Senf at two harvest dates - March 8 and April 3, 1991. |
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Variety |
Dry Wt. T/A |
% N of Tops |
Lbs/A of N in tops |
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|
(lbs. Seed/acre) |
3/8 |
4/3 |
3/8 |
4/3 |
3/8 |
4/3 |
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Phacelia (2.7) |
0.32 |
1.62 |
4.8 |
3.14 |
30.5 |
100.1 |
|
Phacelia (5.3) |
0.60 |
1.89 |
4.4 |
3.11 |
53.3 |
117.4 |
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Phacelia (8.0) |
0.97 |
2.98 |
4.6 |
3.40 |
89.6 |
203.1 |
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White Senf (4.0) |
0.35 |
1.72 |
5.1 |
2.68 |
35.5 |
91.6 |
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White Senf (8.0) |
0.68 |
1.85 |
4.9 |
3.44 |
67.0 |
126.7 |
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White Senf (12.0) |
0.96 |
3.02 |
4.4 |
2.84 |
83.6 |
170.8 |
|
LSD (0.05) |
0.20 |
0.81 |
ns |
ns |
ns |
63.3 |
|
C.V. |
16.80 |
20.42 |
6.5 |
20.3 |
17.5 |
25.8 |
2. COVER CROPS FOR NITROGEN CONSERVATION AND WEED CONTROL
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Trial Specifics |
|
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Cooperator: |
Wayne Shingai, Grower |
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Location: |
San Juan Bautista |
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Planting Date: |
September 5, 1990 |
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Irrigation Date: |
September 7, 1990 |
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Previous Crop: |
Bell pepper |
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Plot Size: |
One 40-inch bed wide by 25 feet long |
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Plot Design: |
Randomized Compete Block Design with Four Reps |
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Treatments: |
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No. |
Varieties |
lbs seed/A |
|
1 |
Lana Vetch |
65.3 |
|
2 |
Lana + Oats |
46 + 25 |
|
3 |
Lana + Oats |
37 + 49 |
|
4 |
Lana + Oats |
13 + 56 |
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5 |
Oats |
84 |
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Harvest Date: |
December 10, 1990 (94 days after irrigation) |
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Harvest Method: |
One square meter was harvested per plot. The weeds and cover crop wereseparated and weighed separately. |
Results
Total pounds of nitrogen in the tops of the cover crops was higher in the oat treatments (see table 1). Lana vetch is exceedingly productive if allowed to mature into the spring, but less so when harvested as it was in this trial. The oats, on the other hand, grew extremely well during the time frame of this trial and had high concentrations of nitrogen in the tops. These results show that oats can absorb much of the residual nitrogen following a vegetable crop. Given the high concentrations of nitrogen in the tops of the oats, it could be expected that they could be discoed in December and would break down readily and leave the ground in good condition for a following spring crop.
The addition of oats to the cover crop mixture substantially reduced
the amount of weed competition (see table 1). Lana vetch had approximately
1/3 ton/acre of weeds, while the addition of even small amounts of oats
reduced weed biomass to 0.01 ton/acre. Lana vetch alone did not produce
as much biomass as when mixed with oats or oats alone. Lana vetch did seem
to have a beneficial effect of increasing the concentration of nitrogen
in the tops of the cover crop mix, except at the lowest seeding rate.
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Table 1. Pounds of weeds, biomass of cover crop, percent nitrogen and pounds of nitrogen produced per acre in each treatment. |
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Variety (lbs seed/A) |
Dry Wt Weeds T/A |
Cover crop Biomass T/A |
% N Tops |
Lbs N in Tops of Cover crops/A |
|
Lana (65) |
0.32 |
1.16 |
4.52 |
103.0 |
|
Lana/Oats (46/25) |
0.01 |
3.81 |
3.45 |
218.5 |
|
Lana/Oats(37/49) |
0.01 |
4.27 |
3.43 |
247.0 |
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Lana/Oats (13/56) |
0.01 |
3.52 |
2.95 |
227.9 |
|
Oats(84) |
0.01 |
3.94 |
2.94 |
231.7 |
|
LSD (0.05) |
ns |
1.67 |
1.10 |
100.4 |
|
C.V. |
264.2 |
29.6 |
20.6 |
27.6 |
3. SEEDING DATE EFFECT ON NITROGEN PRODUCTION OF LANA VETCH
This evaluation was conducted on two fields of Lana Vetch that were grown in the Santa Ana Valley near Hollister by Phil Foster. One field was irrigated on October 15, 1990 and the other on November 1, 1990. The fields were immediately adjacent to each other and gave us a good opportunity to evaluate the effect of a two week difference in planting date during a critical establishment period in the fall. The cover crops were not evaluated for dry weight but only for nitrogen content of the tops by the rule of 16 method (a 4' x 4' area is cut and weighed and multiplied by 16 to calculate pounds of nitrogen that are in the tops-this process was repeated ten times). Table 1 shows that on two evaluation dates-March 28 and April 12, 1991-the October 15th irrigation date yielded greater nitrogen in the tops than the November 1st irrigation date. The differences are not dramatic but if given the opportunity it is clear that the cover crops can respond to an earlier planting date in the fall by yielding more nitrogen per acre in the tops.
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Table 1. Pounds of nitrogen in the tops of Lana Vetch at two irrigation dates- October 15 and November 1, 1990. |
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Irrigation |
Pounds N/A in Tops (two evaluation dates) |
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Dates |
3/28 |
4/12 |
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October 15 |
212.8 |
266.0 |
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November 1 |
165.9 |
241.0 |
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