Previous experiments at the North Willamette Station (1979, 1980) have established that stands of carrot, cauliflower, and lettuce on Willamette silt loam are inhibited at pH less than 5.8 compared to higher pH. In addition, broadcast applications of N fertilizers have reduced stands when compared with unfertilized soil. In the 1979 experiments, ammonium sulfate at 112 kg N/ha depressed stands by approximately 15% to 45%, depending on the crop; at 224 kg N/ha, ammonium sulfate depressed stands by 30% to 55%. On the other hand, calcium nitrate at 112 or 224 kg N/ha did not reduce stands. It was postulated that the effect of ammonium sulfate was caused by lowered soil pH or ammonium-toxicity.
In 1980, a wide range of fertilizers was applied at 224 kg N/ha to attempt to separate the salt injury, ammonium-toxicity, and pH altering effects of the fertilizers. As in 1979, raising the soil pH increased stands. However, unlike 1979, all fertilizers except urea depressed initial stands of carrots and lettuce. The effects of calcium nitrate and ammonium sulfate were about equal. Other fertilizers such as potassium nitrate, ammonium nitrate, and potassium chloride also reduced stands. These fertilizers represent a broad range of soil acidifying potential and salt injury potential. Urea, at 224 kg N/ha, had a lower salt damage potential than the other fertilizers.
In 1981 and 1982, the experiments were designed to shed further light on the stand depressing effects of various N sources and to determine whether incorporation of the fertilizer into the soil would reduce fertilizer effects on stand.
Methods
In 1981, cultivars used were 'Salad Bowl' lettuce and 'Scarlet Nantes' carrot. Main plots [four levels of soil pH, (Table 1)] were in randomized block design, split by three methods of fertilizer application, and these subplots split by application of calcium nitrate, ammonium sulfate or potassium nitrate at 112 kg N/ha and an unfertilized check. Each treatment combination was replicated four times. The application methods were 1) broadcast entire amount before planting, 2) band half the fertilizer (5 cm to the side, 5 cm below the seed row) at planting, broadcast remainder before planting, and 3) band half the fertilizer at planting, broadcast remainder before planting and incorporate into top 5 to 8 cm of soil. All plots were seeded at 30 seeds/m. Stand counts were made 10 days after seeding.
In 1982, treatments were in split-plot factorial design with pH of 5.6, 5.9, 6.2, and 6.6 as main plots, broadcast vs. broadcast and incorporated fertilizer as subplots, and broadcast application of the following fertilizers at 168 kg/ha as sub-subplots: ammonium sulfate, ammonium nitrate, calcium nitrate, nitroform, and unfertilized check. Plots were seeded to 'Salad Bowl' lettuce. Stand counts were made one week after seeding.
Results
In 1981, as in previous years, increasing the soil pH from 5.0 to 6.0 tended to increase stands, but the difference was statistically significant only for lettuce (Table 1). For both lettuce (Table 1) and carrots (Table 2), incorporating the broadcast portion of the fertilizer into the soil clearly prevented the stand-reducing effects of fertilizer application. All fertilizers tended to reduce stands of both crops. Stand reduction was most severe with calcium nitrate. This is in contrast to results in 1979, when calcium nitrate did not depress stands, and also contrasts with results in 1980 when calcium nitrate depressed stands, but no more than ammonium sulfate or potassium nitrate did.
In contrast to 1979, but in agreement with 1980, there was no trend for a significant pH x fertilizer material interaction: raising soil pH did not ameliorate stand reduction effects of one fertilizer more than another fertilizer. There was a significant interaction of application method and fertilizer material in the case of carrots (Table 3). When fertilizer was broadcast or banded and broadcast, fertilizers significantly reduced stands when compared with unfertilized plots. However, when the broadcast portion was incorporated into the soil, fertilizers did not significantly reduce stands.
Table 1. Main Effects of Soil Acidity, Method of Fertilizer Application, and Type of Fertilizer on Seedling Stands of Lettuce, 1981 Soil Lettuce stand Application Lettuce stand Fertilizer Lettuce stand pH (seedlings/m) method (seedlings/m) material (seedlings/m) 5.1 5.5 Broadcast 6.5 None 16.5 5.7 8.5 Band and broadcast 7.0 Ammonium sulfate 9.5 6.2 19.0 Band and incorporate 19.5 Calcium nitrate 5.8 6.6 10.8 LSD (0.05) 4.1 Potassium nitrate 12.0 LSD (0.05) 3.3 LSD(0.05) 5.0 Table 2. Main Effects of Soil Acidity, Method of Fertilizer Application, and Type of Fertilizer on Seedling Stands of Carrots, 1981 Soil Carrot stand Application Carrot stand Fertilizer Carrot stand pH (seedlings/m) method (seedlings/m) material (seedlings/m) 5.1 11.0 Broadcast 9.5 None 14.5 5.7 9.8 Band and broadcast 9.5 Ammonium sulfate 11.3 6.2 12.3 Band and incorporate 15.3 Calcium nitrate 10.8 6.6 12.8 LSD (0.05) 3.6 Potassium nitrate 9.5 LSD(0.05) NS LSD(0.05) 2.1 Table 3. Interaction of Fertilizer Application Method and Fertilizer Material on Seedling StandsZ of Carrots, 1981 ____________________________________________________________________ Application Fertilizer material method None Ammonium Calcium Potassium sulfate nitrate nitrate -----------------seedlings/m ---------------- Broadcast 12.8 10.0 8.3 6.8 Band and broadcast 14.3 7.8 10.5 6.8 Band and incorporate 16.3 15.5 14.5 14.8 ZAveraged over four levels of soil pH. LSD(0.05) = 2.8.
In 1982, the effect of soil pH on lettuce stand was highly significant (Table 4). A soil pH of 6.2 produced the best stands and there were no significant pH x fertilizer or pH x application method interactions. Stands were reduced slightly at pH 6.6 and were lowest at pH 5.6. Incorporation of fertilizer tended to increase stands, but the increase was not significant. Form of fertilizer did not have a significant effect in this trial.
The most useful general conclusion that can be drawn from the four years of this study is that for best stands, soil pH should be near 6.0, pre-emergence fertilizer applications should be moderate, and broadcast fertilizers should be soil incorporated.
Table 4. Main Effects of Soil Acidity and Fertilizer Application Method on Lettuce Stands, 1982 Soil Lettuce stand Application Lettuce stand pH (seedlings/m) method (seedlings/m) 5.6 5.1 Broadcast 8.3 5.9 9.1 Incorporated 10.1 6.2 12.8 LSD(0.05) 1.5 6.6 10.4 LSD(0.05) 1.5