Effect of Soil pH and Nitrogen Fertilizers on Stand Establishment of Small-Seeded Vegetables

Vegetable yields are, within limits, proportional to the initial stand establishment of the crop, i.e. the percentage of seed which successfully germinates, emerges, and commences sunlight-dependent growth. Improvements in stands should increase yields, reduce thinning labor, and may reduce variability in produce size and maturity at harvest. The purpose of this experiment was to determine the effects of soil pH and type (neutral, basic, acid-forming) of N fertilizer on stand establishment of several small-seeded vegetables. It was based on previous observations that low pH and high rates of fertilizer reduce stands. N fertilizers may reduce stand through salt injury, soil pH reduction, or ammonium toxicity. The 1979 trials involved lettuce, carrots, and cauliflower with calcium nitrate and ammonium sulfate the N sources. In the 1980 trials, the crops were lettuce, carrots and spinach, and several more fertilizers were added.

Methods

The cultivars used in the 1979 study were 'Nantes' carrot, 'Ithaca' lettuce, and 'Snowball Y' cauliflower. The experiment was designed as a 4x3x2 factorial with four levels of soil pH (5.0, 5.6, 6.1, 6.4), three rates of N (0, 100, and 200 pounds/acre), and two sources of N (calcium nitrate and ammonium sulfate). Each treatment combination was replicated four times. Soil pH plots were in randomized block design with each plot split into five randomized subplots of 0 N, 100 pounds/acre of N from calcium nitrate, 200 from calcium nitrate, and 100 and 200 pounds/acre from ammonium sulfate. Fertilizers were surface broadcast and not incorporated. Each subplot was then split among the three crops. The sub/subplot for each crop consisted of four rows x seven feet. Between row spacing was two feet. All plots were seeded on June 20 and stand counts made on the middle two rows for each crop on July 2 and July 11.

Cultivars used in the 1980 study were 'Salad Bowl' lettuce, 'Scarlet Nantes' carrot, and 'Melody' and 'Hybrid 424' spinach. The experiments were designed as 4 x 8 factorials with main plots (four levels of soil pH) in randomized block design and the eight fertilizer treatments as subplots. The broadcast fertilizer treatments were as follows: calcium nitrate, 1,300 pounds/acre; ammonium sulfate, 1,000 pounds/acre; ammonium nitrate, 600 pounds/ acre; urea, 435 pounds/acre; calcium nitrate, 750 pounds/acre plus ammonium nitrate, 250 pounds/acre; potassium nitrate, 1,540 pounds/acre; potassium chloride, 600 pounds/acre; and unfertilized check. Thus, each nitrogen-containing fertilizer was applied at 200 pounds/acre of total N. The subplot for each crop consisted of three rows x 10 feet with 20-inch between-row spacing. All plots were seeded on June 23 at a rate of 10 seeds/foot. Fertilizer was broadcast the following day, and stand counts were made at several intervals after seeding.

Results, 1979

Stands of all three crops responded similarly to increasing soil pH and to N application. In each case, raising soil pH from 5.0 significantly increased stand establishment. For carrots, the greatest stand increase occurred between pH 5.0 and 5.6 and best stand was obtained at pH 6.1 (Table 22). Use of calcium nitrate did not affect stand at either 100 or 200 pounds/acre. However, use of ammonium sulfate significantly depressed stand establishment. The higher rate tended to decrease stand more than the low rate of ammonium sulfate, but the difference was statistically significant only at the 90 percent confidence level.

For lettuce, the greatest stand increase occurred between pH 5.6 and 6.2 with a significant decrease at pH 6.4 (Table 23). As with carrots, use of calcium nitrate did not affect stands but ammonium sulfate significantly reduced stand by as much as 50 percent. Again, there was no statistically significant difference in stand between the 100 and 200 pound/acre rates of ammonium sulfate.

For cauliflower, as for lettuce, the greatest stand increase occurred between pH 5.6 and 6.2 with a slight decrease in stand at 12 days when pH was raised to 6.4 (Table 24). As with carrots and lettuce, use of calcium nitrate did not affect stand while ammonium sulfate depressed stand. The 200 pound rate of ammonium sulfate suppressed stand significantly below that obtained with 100 pounds/acre.

For each crop, there was no significant interaction between pH and source or rate of N. That is, higher pH did not reverse or markedly ameliorate the stand-suppressing effect of ammonium sulfate. The effects of low pH and ammonium sulfate were approximately additive. In every case lowest stands occurred with a combination of pH 5.0 and presence of ammonium sulfate fertilizer and highest stands occurred at pH 6.2 or 6.4 with either no applied N or either rate of calcium nitrate.

  Table 22. Effect of Soil pH, and Rate and Source of N on Carrot Stand,   12 Days after Seeding - 1979                                                                                         Soil pH         N source and rate                5.0   5.6   6.1   6.4                                                        Stand, seedlings/foot  Mean, fertilizer  Zero N check                     5.0   6.6   7.8   7.3    6.7  Ammonium sulfate, 100 lb/acre    3.0   5.5   6.4   6.2    5.3   Ammonium sulfate, 200 lb/acre    2.0   5.0   6.4   5.1    4.6   Calcium nitrate,  100 lb/acre    4.7   7.0   7.3   6.7    6.4  Calcium nitrate,  200 lb/acre    5.2   6.6   7.0   6.5    6.3              	  Mean, pH                         4.0   6.2   7.0   6.4    Overall mean: 5.9  LSD(.05)pH = 0.6; LSD(.05 )Fertilizer = 0.7.      Table 23. Effect of Soil pH, and Rate and Source of N on Lettuce Stand,   12 Days after Seeding - 1979                                                                                         Soil pH         N source, rate                   5.0   5.6   6.1   6.4                                                        Stand, seedlings/foot  Mean, fertilizer  Zero N check                     2.5   2.4   5.9   3.8    3.7  Ammonium sulfate, 100 lb/acre    1.2   1.3   3.5   2.3    2.1  Ammonium sulfate, 200 lb/acre    0.7   1.6   3.3   1.9    1.8   Calcium nitrate,  100 lb/acre    1.3   3.2   5.2   4.2    3.5   Calcium nitrate,  200 lb/acre    1.6   4.3   5.4   3.4    3.7                Mean, pH                         1.5   2.6   4.7   3.1    Overall mean: 3.0  LSD(.05)pH = 0.6; LSD(.05) Fertilizer = 0.6      Table 24. Effect of Soil pH, and Rate and Source of N on Cauliflower Stand,   12 Days after Seeding - 1979                                                                                         Soil pH         N source, rate                   5.0   5.6   6.1   6.4                                                        Stand, seedlings/foot  Mean, fertilizer  Zero N check                     5.1   5.3   7.2   7.0    6.1  Ammonium sulfate, 100 lb/acre    4.0   4.2   6.0   6.2    5.1   Ammonium sulfate, 200 lb/acre    3.1   3.7   5.4   5.1    4.3   Calcium nitrate,  100 lb/acre    5.1   6.2   8.0   6.1    6.3   Calcium nitrate,  200 lb/acre    5.1   5.3   7.4   5.9    5.9                Mean, pH                         4.5   4.9   6.8   6.1    Overall mean: 5.6  LSD(.05) pH = 0.7; LSD(.05) Fertilizer = 0.8  

Results, 1980

In the 1980 experiments, stand of lettuce was initially depressed by all fertilizers except urea (Table 25) but the effect diminished with time (data not shown). Stand of carrots was affected similarly (Table 26); all fertilizers except urea inhibited stand establishment with ammonium sulfate and potassium chloride causing the greatest inhibition. Considering the relative acidity and salt injury potential of the treatments (Table 27), the lack of stand depressing effect of urea can best be explained by a relatively low salt damage potential. However, potassium nitrate has a high salt damage potential but did not depress stand more than did other treatments with more moderate salt damage potential.

Calcium nitrate and ammonium sulfate did not differ appreciably in their effect on stand in 1980. In general, a surface broadcast application of the complete crop fertilizer needs appears to inhibit stand establishment.

Soil pH had less effect on stand than in previous experiments. Only in the case of carrots and spinach (Table 28) did low soil pH significantly inhibit stand establishment. The fertilizer treatments had no significant effect on spinach stand and the data are not shown. Yield of spinach responded markedly to increasing soil pH (Table 29). At pH 5.0, the emerged seedlings failed to make any harvestable growth. Maximum yields occurred at pH 6.4 for both cultivars.

  Table 25. Effect of Soil pH and Fertilizer on Lettuce Stand,   13 Days after seeding - 1980                                                                                    Soil pH         Fertilizer                     5.0   5.6  6.1   6.4                                                       Stand, seedlings/foot  Mean, fertilizer  Zero N Check                   5.0   4.7  5.7   6.0     5.3  Calcium nitrate                3.7   2.3  4.3   3.3     3.3   Ammonium sulfate               3.3   3.0  3.3   3.3     3.3   Ammonium nitrate               4.3   3.0  4.7   5.0     4.3  Urea                           3.3   4.3  4.0   4.0     4.0   Cal. nit. + amm. nit.          3.0   2.7  4.0   4.0     3.3   Potassium nitrate              4.0   3.0  3.3   4.7     3.3   Potassium chloride             2.3   3.0  3.3   3.3     3.3                Mean, pH                       3.7   3.3  4.0   4.3     Overall mean: 3.8  LSD(.05) Fertilizer = 0.7      Table 26. Effect of Soil pH and Fertilizer on Carrot Stand, 20 Days  after Seeding - 1980                                                                                             Soil pH         Fertilizer                     5.0   5.6   6.1   6.4                                                           Stand, seedlings/foot  Mean, fertilizer	  Zero N check                   3.7   4.3   5.3   5.3    4.7  Calcium nitrate                4.0   3.0   4.0   3.7    3.7   Ammonium sulfate               1.7   3.0   2.7   3.3    2.7  Ammonium nitrate               3.0   2.3   3.7   3.0    3.0   Urea                           2.7   3.3   4.3   2.7    3.3   Cal. nit. + amm. nit.          2.7   3.3   4.0   4.0    3.7  Potassium nitrate              2.3   2.7   3.3   2.3    3.7   Potassium chloride             3.0   3.7   3.7   3.3    2.7                Mean, pH                       3.0   3.3   4.0   3.3    Overall mean: 3.8	  LSD(.05) pH = 0.5; LSD(.05) Fertilizer = 0.6      Table 27. Relative Acidity and Relative Salt Damage Potential of Fertilizers                                    Relative AcidityZ	    Relative SaltY  Fertilizer                        pounds CaC03 equiv.      Damage Potential   Control                                    0                     0   Calcium nitrate                          292 (basic)           772   Ammonium sulfate                        1243                   773   Ammonium nitrate                         416                   706   Urea                                     409                   365   Calcium nitrate + ammonium nitrate        20                   739   Potassium nitrate                          0                  1277   Potassium chloride                         0                   766            ZPounds CaC03 equivalent for the amount of fertilizer used per acre.  YAmount of fertilizer used (x) salt index.      Table 28. Effect of Soil pH on Stand of Spinach - 1980                              Stand, seedlings/foot  Soil pH                     Hybrid 424     Melody       5.0                            7.7 a        9.0 a   5.7                            9.0 a        9.3 a   6.1                           10.7 b       12.7 b   6.4                           10.7 b       12.0 b     	      Table 29. Effect of Soil pH on Yield of Spinach - 1980                             Yield, tons/acre    Soil pH                 Hybrid 424     Melody           5.0                         0 a          0 a   5.7                       3.0 b        2.5 b   6.1                       7.5 c        5.5 c   6.4                      11.4 d        6.6 c            

Share