Sweet corn yields in the Willamette Valley increase with application of lime and banded P fertilizers, even in the presence of high levels of available soil P. However, the interaction of applied lime, which increases P availability, and applied P has not been explored in detail. Many sources of P are available. These P materials vary both in P content and in the water-solubility of the P compounds present. The effects of various P sources and their interactions with soil pH (lime applied) have not been widely studied The objective of these experiments was to investigate the effect of different sources of P at two different P rates, and with or without lime, on yield of 'Jubilee' sweet corn.
Methods
Lime was broadcast and disked into a Willamette silt loam soil al rates of 0 or 3 tons/acre in March 1982, with four replications of each treatment. On June 2, 1983, the lime strips were split at seeding by a band application of six different nominal ammonium phosphate materials at 50 or 150 pounds P205/acre. Application rate was based on the labelled citrate-soluble P205. Within each P rate strip, the six P sources were randomly applied to 2 row subplots of 30-foot length. All plots received a total of 200 pounds N/acre and were irrigated as needed. In 1984, a uniformly limed area was used. Treatments included a check with no P fertilizer, three P sources banded at 50 pounds P205/acre and one source banded at 150 pounds P205/acre. All plots received a total of 190 pounds N/acre.
Results and Discussion
The measured water-solubility (presumed plant availability) of the 1983 P sources varied from 49% to 5% (Table 1). If P sources are applied at equal rates of total P, plant response might be expected to vary with the water-solubility of the P materials. Yield of mature ears was affected by P source (Table 2), and, in general, higher yields were obtained with the more water-soluble P sources. This correlation of yield of mature-ear with P source water-solubility was particularly strong at 50 pounds P205/acre and either rate of lime (Table 1). At the higher rate of P205, sufficient P may be plant available even at lower water-solubility.
Neither lime rate nor P rate significantly affected yield of mature ears or total ear yield in 1983 because of insufficient replication. Source of P had no effect on total ear yield.
Mean ear weight of mature ears was greater at the higher rate of P than at the lower rate when averaged over lime rates and P sources. Lime and P source did not affect mean weight of mature ears (Table 2) and there were no significant interactions affecting mean weight of mature ears.
Both P rate and P source significantly affected the mean weight of all ears (mature plus immature). Mean ear weight was greater at the higher rate of P Table 2). Ear weight correlated strongly with P source solubility: ear weight was greatest with the most soluble P source and smallest with the least soluble P source. As with mature ear yield, the correlation was stronger at the lower than at the higher rate of total P (Table 1).
Table 1. Water solubility of nominal ammonium phosphate P sources and interaction of P source and P rate on yield of mature ears and mean ear weight of 'Jubilee' sweet corn, 1983 P205 (lb/A) Water 50 150 soluble Yield of Mean weight Yield of Mean weight P source P205 mature ears of all ears mature ears of all ears % T/A lb T/A lb 1 49 6.9 0.69 6.6 0.70 2 41 5.7 0.68 5.8 0.69 3 40 5.2 0.67 6.3 0.70 4 29 5.5 0.67 6.5 0.71 5 16 5.3 0.66 5.9 0.69 6 5 4.4 0.63 5.8 0.67 LSD (0.05) for different P sources at same P rate = 2.2 yield, 0.05 for ear weight. LSD (0.05) for different P sources at different P rates = 2.5 for yield, 0.05 for ear weight. Table 2. Main effects of lime, P rate and P source on yield and mean ear weight of Jubilee sweet corn, 1983 Yield of Yield of Mean weight of Mean weight of Treatment mature ears all ears mature ears all ears -----------T/A-------- -------------lb/ear------------ Lime, 0 T/A 5.6 8.6 0.73 0.67 3 T/A 6.1 8.9 0.74 0.69 NSZ NS NS NS P205, 50 lb/A 5.5 8.6 0.72 0.67 150 lb/A 6.1 8.8 0.74 0.69 NS NS * ** P source, 1 6.7 9.3 0.74 0.70 2 5.7 8.7 0.73 0.68 3 5.8 8.7 0.74 0.69 4 6.0 8.7 0.74 0.69 5 5.6 8.5 0.73 0.68 6 5.1 8.4 0.70 0.65 LSD(0.05) 0.8 NS NS 0.03 Z**,*,NS: significant at 1% and 5% levels, and non-significant respectively. Table 3. Effects of P sources on sweet corn yields, 1984 Total P2O5 Plant Ht. Mature ear Total Mean ear wt. Treatment Citrate-soluble Water-soluble on July 5 yield yield Mature Total ------------lb/A------------- inches ------- T/A------ -----lb------ 1 150Z 150 11.3 10.0 11.2 0.76 0.74 2 50Z 50 10.2 7.6 10.0 0.73 0.67 3 50Y 41 10.6 8.9 10.0 0.76 0.73 4 50Y 30 9.6 7.5 9.5 0.75 0.67 5 0 0 8.6 7.6 9.6 0.73 0.68 LSD(0.05) 2.1 1.9 1.2 0.03 0.05 ZMonoammonium phosphate. YUrea phosphates.
In 1984, plant growth and yield did not correlate with amount of water-soluble P banded at planting, mainly because of higher yields, ear weights, and plant height with Treatment 3, than with Treatment 2. Ear yields were highest with 150 pounds P in the band and lowest with 30 pounds P (Table 3). Mean ear weights were lowest with no P in the band.
The 1984 results do not provide strong confirmation of 1983 results. More work will be necessary to determine the importance of water-solubility of P sources.