The purpose of these experiments was to investigate cultural methods for establishing earlier and higher percentage stands of several vegetable crops and to encourage more vigorous seedling growth during periods of suboptimal air and soil temperatures. Phosphoric acid (PA), a possible emergence stimulator and anticrustant, was applied at planting as an over-the-row banded spray. This technique, if successful, would allow production of crops at earlier than normal dates, taking advantage of possible premium prices. Better stand establishment could allow direct seeding of presently transplanted crops or eliminate the need for over-seeding and subsequent thinning of some crops.
Methods
Crops tested were cauliflower, bush beans, carrots, cucumber, and head lettuce at the Station, rutabaga, parsnip, and turnip at Montecucco Farms north of Canby, carrots at Casale Farms, Aurora, and leaf lettuce, Romaine lettuce, spinach, and green onions at the Sambuceto farm, Lone Elder. At the Station, the plot area was prepared by plowing, disking, incorporation of 1,000 pounds/acre of 10-20-10 plus 500 pounds/acre of dolomite and harrowing to achieve final seedbed. The cauliflower area also received 4 pounds/acre dyfonate incorporated into the top three inches of the seedbed along with 0.75 pounds/acre of trifluralin. The bean and cucumber plots received 4 pounds/acre dinitroamine and the carrot area, 1.5 pounds/acre linuron, all preemergence.
Seeding of cauliflower, beans, cucumbers, and carrots and PA application was on April 10 and all plots received 100 pounds/acre of 18-46-0 banded at planting. PA was applied at seeding to the appropriate plots (40 row feet) at a rate of 20 gallons/acre of 17 percent PA in a 2-inch band over the row. This is roughly equivalent to 600 pounds of P205/acre within the sprayed band. Applications at grower's farms were on April 10 and April 11. In these cases, the PA was applied within 48 hours of seeding but before emergence of the crop. Each crop was seeded and grown according to the particular grower's usual cultural practice. The head lettuce experiment was seeded on June 2. All experiments were replicated at least four times. Stand data were obtained for all crops except cucumber. Yield data were obtained for Station crops only.
Results
An over-the-row band of PA at or shortly following planting tended to increase stand for all crops except leaf and Romaine lettuce (Table 9). However, statistically significant (95 percent probability) increases in early stand were obtained only for spinach and cauliflower while crisphead lettuce and onion stands were significantly improved only at the 90 percent confidence level. High variability among blocks was the key factor in the lack of statistically significant stand differences for most crops. In the case of bush beans, the variability was directly attributable to birds eating the emerging seedlings. The cucumber crop was destroyed by birds eating the seed. The high variability among plots for Station carrots was caused in part by an apparent failure to properly seed one check plot.
The increased stands of cauliflower, crisphead lettuce, and onion were reduced to non-significant levels within four weeks after seeding (Table 10). This was caused in part by a combination of damping off and insect damage which led to increased variability among blocks and also to late emergence of seedlings from untreated plots. Average daily temperature during the period April 10 to May 1 was 50°F, average daily soil temperature at 2-inch depth was 53°, clearly suboptimal for most of these crops. Total precipitation was 0.5 inches but little crusting was observed at any location except Casale Farms. Although crusting was not a major factor, the low air and soil temperatures should have provided a nearly ideal test of any emergence and growth stimulating properties of the PA.
Cauliflower and lettuce crops were thinned to a final stand and seedling weights were obtained shortly before or at thinning. Seedlings from PA sprayed plots weighed significantly more than seedlings from non-sprayed plots for crisphead and leaf lettuce (Table 11). In addition to these effects on mean seedling weight, PA treated plots of cauliflower and lettuce exhibited a lower degree of among-blocks variation as seen in the smaller coefficients of variability for PA treatment means.
Stand establishment, within limits, is assumed to be related to yield. Unfortunately, of the crops which showed significant stand differences, no yield data were obtained for onions or spinach and the cauliflower and crisphead lettuce were thinned to a nearly uniform stand. However, it should be noted that the stands of cauliflower and crisphead lettuce from PA-treated plots approached the 90-100 percent level needed for direct seeding to final stand.
Of the crops for which yield data were obtained, PA treatment significantly increased yield only for carrots (Table 12). The increased carrot yield was due primarily to improved stand. Mean root size was increased by 11 percent but this difference was not statistically significant. For crisphead lettuce, the 6 percent increase in mean head weight for plants from PA plots was not statistically significant but the head size variability (per head basis) was 28 percent smaller on PA treated plots. This degree of improvement could be important for a mechanically harvested crop, particularly as it may reflect more concentrated maturity. Cauliflower head size variability was not similarly affected.
Table 9. Early Stand Counts as Affected by PA Spray Crop Days after Seedlings/plot Significant seeding +PA -PA difference Bean 21 39.0 27.3 - Carrot (Casale) 19 78.0 75.6 - Carrot (Station) 21 177.3 138.0 -Z Cauliflower 17 150.8 133.6 ** Lettuce, crisphead 6 53.5 46.2 * Lettuce, leaf 15 48.8 48.7 - Lettuce, Romaine 15 28.0 30.7 - Onion 19 223.0 205.5 * Parsnip 16 52.8 46.5 - Rutabaga 16 18.2 17.8 - Spinach 15 80.3 69.7 ** Turnip 18 36.4 33.8 - ZHighly variable among blocks. **Significantly different at 95 percent confidence level. *Significantly different at 90 percent confidence level. Table 10. Late Stand Counts as Affected by PA Spray Crop Days after Seedlings/plot Significant seeding +PA -PA difference Beans 25 45.8 38.3 - Beans 30 76.3 62.5 - Carrots (Station) 28 161.0 117.3 - Cauliflower 25 144.8 130.0 - Lettuce, crisphead 12 50.2 48.8 - Table 11. Seedling Weight at Thinning as Affected by PA Spray Crop Days after +PA -PA Significant seeding Fresh weight Fresh weight difference (mg/seedling) C.V. (mg/seedling) C.V. Cauliflower 37 1150 10% 1160 21% - Lettuce, crisphead 25 998 2 745 4 ** Lettuce, leaf 40 720 6 510 9 ** Lettuce, Romaine 40 760 4 660 7 - Table 12. Vegetable Yields as Affected by PA Spray Crop +PA -PA Significant Mean fresh Mean fresh difference weight C.V. weight C.V. Beans, kg/plot 6.51 41% 6.82 41% - Carrots (Station), kg/plot 5.73 32 4.36 50 ** Carrots (Station), g/root 72 11 65 11 - Cauliflower, g/head 569 30 580 31 - Lettuce, crisphead, g/head 611 13 576 18 - _______________________________________________________________________________________________ ZThis C.V. is among heads.