Response of Small-Seeded Vegetables to Several Anticrustants

Poor stand establishment is often a limiting factor in vegetable production in the Willamette Valley. Carrots, onions, and lettuce, in particular, often fail to emerge because of soil crusting. Most small-seeded crops lack the vigor necessary to emerge when resisted by significant soil impedance. A high degree of impedance or crusting (also known as soil mechanical resistance) is caused by breakdown of soil particle aggregates. Several treatments exist which may reduce the breakdown of aggregates.

Phosphoric acid (PA) has been tested extensively at the North Willamette Station as well as elsewhere in Oregon. Results with PA banded over the seed row have been inconsistent. In some years, crusting has been reduced and stands increased, but in other years, PA has not improved stands. The objectives of these experiments were to 1) investigate further the effectiveness of PA as an anticrustant/ emergence stimulator and 2) compare it to other materials such as Nalco 2190 (organic polymer), vermiculite, and neutral ammonium phosphate solution (10-34-0), 3) determine to what degree the emergence and yield stimulating effect of PA can be reproduced by banding concentrated superphosphate, 4) compare the effectiveness of PA and other anticrustants at low vs. higher soil temperature, and 5) determine whether soil pH and Ca content affects the emergence stimulating properties of PA.


Experiment 1.
In 1979, Objective 1 was approached by seeding several crops with and without PA and measuring stands, soil mechanical resistance (MR), yields and leaf P levels. The crops and varieties involved in this experiment were 'Ithaca' head lettuce, 'Waldmann's Green' leaf lettuce, 'Snowball Y' cauliflower, 'Melody' spinach, 'Pickmore' cucumber, 'Nantes' carrot, and 'Japanese Bunching' onion. The plot area was prepared for seeding in late April after plowing down 1,000 pounds/acre of 10-20-10. The area to be planted to cauliflower received a preplant, incorporated application of trifluralin at 0.75 pounds/acre. A very finely pulverized seedbed was prepared by rototilling and packing to encourage optimal conditions for crusting.

All crops were seeded on May 2. PA applications were made to appropriate plots immediately after seeding at a rate of nine ounces of 17 percent acid per 25-foot plot. PA treatment and check were replicated six times in a randomized block design. Plot size was three rows x 25 feet for each crop. Between row spacing was 30 inches. Weed control was by post-plant herbicide applications on May 3 and later by hand cultivation. Herbicides used were CDEC at 3 pounds/acre for lettuce and spinach, dinitroamine at 3 pounds/acre for cucumbers, CDAA at six pounds/acre for onions, and linuron at 1.5 pounds/acre for carrots. Irrigation was by overhead sprinkler as needed.

Experiment 2.
In 1980, objectives 2 and 3 were approached by seeding five crops with seven anticrustant or emergence stimulation treatments on April 30. The plot area received a broadcast application of 1,000 pounds/acre of 10-20-10. The five crops were 'Sentinel' onion, 'Snowball Y' cauliflower, 'Waldmann's Green' lettuce, 'Marketmore' cucumber, and 'Scarlet Nantes' carrot. Treatments were 1) check, 2) vermiculite at 12 cubic feet/acre, 3) PA, 17 percent by volume, at 160 ml per 20 row feet (31 pounds P/acre), 4) banded 0-45-0 at 31 pounds P/acre, 5) combination of 3 and 4, 6) neutral ammonium phosphate solution at 31 pounds P/acre, 7) Nalco 2190, 10 percent by volume, at 132 ml per 20 feet (25 gallons/acre). Each treatment was replicated four times in a randomized block design. Stand counts and soil MR were measured at several intervals following seeding. MR was measured with a Technical Products Co. pressure tester. Plots were harvested at maturity of crop (except cauliflower). Herbicides used were linuron (carrots), dinitroamine (cucumbers), pronamide (lettuce), and nitrofen (onions, cauliflower).

Experiment 3.
Objective 4 was met by repeating Experiment 2 with a seeding date of July 1. Treatments 4 and 5 were eliminated. Only stand counts were made. Crops were onion, carrot, and lettuce.

Experiment 4.
(Objective 5). 'Waldmann's Green' lettuce and 'Scarlet Nantes' carrots were seeded on May 15, 1980, on long term lime plots. Main plots consisted of soil treatments of four tons/acre lime, eight tons/acre lime, one ton/acre sulfur, and untreated check. Resulting pH was approximately 6.1, 6.4, 5.0, and 5.6, respectively. Subplot treatment was PA at 31 pounds P/acre vs. untreated check. All eight treatments combinations were replicated four times. Stand counts were made at several intervals after seeding. No fertilizer or pesticides were used.

Results and Discussion

Experiment 1.
In 1979, seedling stands were significantly greater on PA-treated plots for all crops (Tables 30, 31). Cauliflower, lettuce, and spinach responded less to PA application than did onion, carrot, and cucumber. Even on PA-treated plots, only onion and cucumber achieved commercially acceptable stands. Lettuce and cauliflower were replanted in June and, again, PA increased stands of each crop, but not to an acceptable level (data not shown). Several crops were carried through to harvest and yields are shown in Table 32. PA significantly increased yield of cucumber, carrot, onion, leaf and head lettuce. There was a trend toward increased root size for carrot and increased bulb weight for onion on PA-treated plots, but in neither case was the difference statistically significant. Most of the yield increase can be attributed to increased stands.

Are the increases in stand with PA because of an anticrustant effect, increased availability of P, pH effect, or some other cause? Previous work with PA has demonstrated a very slight and probably biologically insignificant increase in soil temperature at the 1-inch depth. PA decreases soil pH in the surface few millimeters but on the already acid soil (pH 5.5) used in this experiment, a decrease in pH probably would depress stands. Soil P levels were raised from 130 ppm to 177 ppm at the half-inch depth by PA application and leaf P content was significantly increased for onion, carrot, and lettuce from PA-treated plots at five weeks after seeding (Table 33). Thus, at least a part of the PA effect may be caused by availability of P to the emerging and growing seedling.

The anticrustant effect of PA, resulting in decreased resistance to cotyledon emergence (Table 34), also appears to play a large role. The soil MR units in Table 34 are measured on a spring-loaded 2-mm diameter plunger which is 4orced into the surface inch of soil. A reading of 1,000 is equal to 3.2 x 104 g/cm2 or 3.l x 106 Pa. Other research has established that most small-seeded vegetables will not emerge if the resistance exceeds 1,000 units. At six and eight days after seeding, the resistance was low and did not differ with treatment. Soil moisture was high at this time and progressively decreased during the following eight days of zero precipitation. Considerable crusting occurred during this period on both treated and untreated plots, but the PA treated plots always had significantly lower MR. A one inch irrigation occurred on the seventeenth day after planting. MR readings again decreased but the difference between treated and untreated plots was maintained.

Thus, it appears that the stand promoting effect of PA is caused by both an anticrustant action and availability of soil P.

  Table 30. Stand of Vegetables as Affected by Phosphoric Acid (PA) Application,   13 Days After Seeding - 1979                                                                           Stand, seedlings/foot  Crop                +PA  C.V.  -PA  C.V.   Significance                         Leaf Lettuce        3.4   60   1.8   65         *Z  Head Lettuce        2.0   39   1.1   84         *  Spinach             1.2   32   0.5   91         *  Carrot              1.9   78   0.6   71         *  Onion               8.0   73   2.7   53         **  Cauliflower         0.8   57   0.4  103        N.S.                             ZSingle asterisk: Means are significantly different at 95% confidence level.   Double asterisk: Means are significantly different at 99% confidence level      Table 31. Stand of Vegetables as Affected by PA Application, 21 Days   after Seeding - 1979                                                                          Stand, seedlings/foot  Crop                    +PA   C.V.   -PA   C.V.   Significance        Leaf Lettuce            4.7    36    2.3    44	      **  Head Lettuce            2.4    26    1.2    65         *  Spinach                 1.9    28    1.5    36        N.S.  Carrot                  9.2    46    2.7    30	      **  Onion                  40.3    22   22.1    20	      **  Cauliflower             1.3    47    0.6    54         *  Cucumber                9.9    23    6.6    21         *                  Table 32. Yield of Vegetables as Affected by PA Application - 1979                          Yield, tons/acre  Crop                     +PA       -PA           Significance       Cucumber                11.0       6.4                 *  Carrot, total           10.6       3.4                **  Onion                    8.0       3.6                 *  Lettuce, leaf            8.0       6.6                 *  Lettuce, head           10.3       7.8                 *                Table 33. Effect of PA on Leaf Phosphorus Content of Vegetable Seedings,   5 Weeks after Planting                                                                 Leaf P Content, percent dry wt.   Crop            +PA            -PA                    Significance        Onion          0.32           0.26                         *  Carrot         0.20           0.16                         *  Lettuce        0.36           0.26                        **              	    Table 34. Soil Mechanical Resistance as Affected by PA Application - 1979  Days after        Soil Mechanical ResistanceZ  Seeding            +PA                   -PA              Significance     6                  239                   287                  N.S.  8                  252                   276                  N.S.  9                  417                   557                   **  12                 450                   827                   **  16                 905                  1483                   **  21                 582                   924                   **          ZAverage of 12 readings/plot, six replications/treatment.  

Experiment 2



Mean soil temperature at two-inch depth during the stand establishment phase of this experiment (April 30 - May 22, 1980) was 63°F. MR readings (Table 35) represent the mean of four replications, 10 readings per plot. The treatment most effective in minimizing MR was vermiculite; PA was the second most effective treatment, followed by Nalco 2190. The mechanism of neutral ammonium phosphate reduction of MR is not known but may involve phosphate binding with soil particles. Concentrated superphosphate banded two inches beneath and two inches to the side of the seed row also reduced MR, perhaps caused by the rough condition of the soil surface left by the fertilizer delivery shoe. Based on reduction of MR, all treated plots might be expected to produce greater stands than the control plots.

For lettuce, vermiculite was by far the most effective emergence stimulator with PA and Nalco less effective; ammonium phosphate solution had no effect (Table 36). After 22 days, the vermiculite treated plots showed a better than 400 percent stand improvement over control. For carrots, vermiculite was also most effective (Table 37). After 22 days, vermiculite-treated plots exhibited a 260 percent improvement in stand over the control.

Results with onion were not as striking. Vermiculite, and to a lesser extent, PA promoted early emergence, but final stand was not affected by treatment (Table 38). Results with cauliflower also were less striking than with carrots or lettuce. Only vermiculite increased the final stand (Table 39). Vermiculite was also the only treatment to significantly increase the final stand of cucumber (Table 40). PA promoted early emergence as did ammonium phosphate, but other treatments had no effect.

In summary, vermiculite was by far the most effective anticrustant and emergence stimulator. PA was moderately effective at this planting date. Other treatments usually had no statistically significant effect although banded superphosphate alone occasionally tended to inhibit stand establishment, perhaps because of a salt effect. Other research results have demonstrated that the effectiveness of Nalco 2190 may be greatly increased by incorporating the material into the soil rather than using an over-the-row spray.

Leaf lettuce stands were not thinned. Plots were harvested 71 days after seeding. Yields were proportional to the final stand (Table 41). Highest yield was obtained on the vermiculite-treated plots and lowest yield on the treble superphosphate plots. Lettuce on the neutral ammonium phosphate plots yielded higher than would be expected from the final stand. This may be caused by the extra N (nine pounds/acre) applied to these plots with the anticrustant treatment.

Carrot yields followed much the same pattern as lettuce except that ammonium phosphate did not increase yield. Vermiculite plots had the highest yields, followed by PA-treated plots. There were no significant differences among onion yields in agreement with the lack of a significant treatment effect on final onion stand. Cucumber yields at first picking were proportional to the final stand with only the vermiculite plots outyielding controls. Subsequent cucumber pickings produced no statistically significant yield differences, although plants tended to yield the highest on superphosphate-treated plots.

Experiment 3.
Mean soil temperature at two-inch depth during the stand establishment phase of this experiment (July 1 - July 14) was 73°F, a favorable temperature for germnation. MR readings were not made. As with the earlier planting, vermiculite was the most effective emergence stimulator for lettuce, producing both earlier emergence and greater final stand (Table 42). PA and Nalco 2190 were moderately effective while neutral ammonium phosphate had no effect. Emergence of carrots and onions was more rapid with vermiculite but no treatment had any effect on final stand of these crops. Apparently soil temperature and lack of crusting conditions were nearly. ideal for crop emergence at this planting date.

Experiment 4.
For both lettuce and carrot, stands increased with increasing soil pH with a maximum at pH 6.1 (data not shown). In this experiment, PA had no significant effect on stand; therefore, the effect of soil pH or Ca content on the emergence stimulating/anticrustant effect of PA could not be determined.

Table 35. Soil MR Eight and Twenty Days after Seeding - 1980                                     Soil MR              Treatment               Eight Days         Twenty Days        Control, no treatment     695 fZ               831 e   Vermiculite               148 a                285 a   Phosphoric acid           304 b                305 a   Superphosphate            555 e                688 d   PA plus superphosphate    341 be               579 cd   Ammonium phosphate        496 d                436 b  Nalco 2190                383 c                483 bc         ZMeans within a column which are followed by same letter are    not significantly different at 95% level of confidence.      Table 36. Stand of Lettuce at Several Intervals after Seeding on April 30, 1980                                      Stand, seedlings/twenty feet               Treatment               5 days   7 days   9 days   12 days   14 days  22 days  	  Control                  0 a       4 a     11 a      28 ab    30 ab    33 ab      Vermiculite             68 b     153 b    160 c     160 d    164 d    141 d  PA                       l a      17 a     38 b      53 c     54 c     54 c  Superphosphate           0 a       4 a     11 a	     21 a     21 a     24 a  PA plus superphosphate   1 a      14 a     26 ab     38 abc   39 abc   42 abc  Ammonium phosphate       3 a      11 a     29 b	     40 abc   40 bc    39 abc  Nalco 2190               2 a      14 a     31 b      43 bc    48 bc    49 bc         Table 37. Stand of Carrots at Several Intervals after Seeding on April 30, 1980                                     Stand, seedlings/twenty feet            Treatment              9 days    12 days    14 days    19 days    22 days      	  Control                 1 a      18 ab        28 a      42 ab      40 ab   Vermiculite            15 c      92 e         94 c     114 c      103 c   PA                      2 a      43 d         53 b      51 b       63 b  Superphosphate          1 a      15 a         24 a      23 a       26 a   PA plus superphosphate  2 ab     39 cd        53 b      66 b       68 b   Ammonium phosphate      3 b      21 abc       29 ab     49 b       41 ab  Nalco 2190              3 b      35 bcd       44 ab     57 b       54 ab             Table 38. Stand of Onions at Several Intervals after Seeding  on April 30, 1980                                                                         Stand, seedlings/twenty feet      Treatment             9 days   12 days   14 days   19 days  	  Control                 1 a      31 a      104 b    134 a  Vermiculite            24 b     104 c      126 c    118 a  PA                      1 a      50 b      112 bc   116 a  Superphosphate          0 a      26 a       82 a    113 a  PA plus superphosphate  1 a      36 ab     101 b     99 a  Ammonium phosphate	1 a      37 ab     107 b    130 a  Nalco 2190              1 a      39 ab     114bc    126 a         Table 39. Stand of Cauliflower at Several Intervals after Seeding on  April 30, 1980                                                                                       Stand, seedlings/twenty feet           Treatment              7 days    9 days   12 days   14 days  22 days	  Control                  6 ab     32 ab    61 ab     67 b     51 a   Vermiculite             68 d      79 e     81 d      81 c     79 b   PA                      14 bc     55 d     76 cd     80 c     58 a  Superphosphate           4 a      20 a     51 a      54 a     46 a   PA plus superphosphate  12 abc    46 cd    66 be     72 bc    46 a   Ammonium phosphate       5 ab     34 be    63 ab     64 ab    53 a  Nalco 2190              17 c      46 cd    71 bcd    73 bc    56 a        Table 40. Stand of Cucumber at Several Intervals after Seeding on   April 30, 1980                                                                                    Stand, seedlings/twenty feet      Treatment                  9 days   12 days   14 days   22 days    Control                      3 a     31 ab       38 a    38 a   Vermiculite                 34 d     60 c        61 b    55 b   PA                          22 c     43 b        46 a    45 ab  Superphosphate               4 a     27 a        36 a    42 ab   PA plus superphosphate      11 b     40 ab       44 a    43 ab  Ammonium phosphate          13 b     37 ab       40 a    40 ab  Nalco 2190                   7 ab    34 ab       38 a    38 a         Table 41. Effect of Anticrustant Treatments on Yield of Crops Seeded  on April 30, 1980                                                                                       Yield, tons/acre               Treatment              lettuce     cucumberZ  carrot    onion  ___________________________________________________________________________________________  Control                 6.8 ab      10.1 a    4.0 ab    16.9 ab   Vermiculite            13.4 c       18.6 b    8.9 c     20.4 b   PA                      9.1 b        8.0 a    6.8 bc    19.6 b  Superphosphate          4.6 a       12.0 a    2.5 a     13.5 a   PA plus superphosphate  7.2 ab      12.8 ab   5.6 b     16.9 ab   Ammonium phosphate      9.5 b        8.3 a    3.9 ab    16.9 ab  Nalco 2190              8.3 b        9.2 a    5.8 b     18.1 b        ZYield at first harvest, no significant cucumber yield differences    at subsequent harvests.      Table 42. Stand of Lettuce at Several Intervals after Seeding  on July 1, 1980                                                                              Stand, seedlings/twenty feet      Treatment                     7 days     9 days     14 days    Control                        2 a        13 a        18 a   Vermiculite                   78 c       113 c       120 c   PA                             5 ab       25 b        44 b   Ammonium phosphate             7 b        15 a        21 a  Nalco 2190                     4 ab       25 b        36 b