In 2000, sufficient rainfall contributed to good crop establishment and growth overall. Oats appeared to respond well to cool conditions that prevailed throughout the early part of the growing season. However, heavy rains later in the growing season contributed to crop lodging.
Plant stand was not affected by fertilizer treatment at either experimental site. However, at the clay loam site, treatments receiving KCl tended (P=0.07) to have slightly lower plant densities than those not receiving KCl.
Although fertilization had little effect on plant stand, panicle density was influenced by fertilizer treatment. At the clay loam site, both N and P application resulted in a statistically significant linear increase in panicle density. At the sandy loam site, a statistically significant N*P*K interaction was evident; however, the agronomic significance of this interaction was not clear. Overall, N and P increased panicle density at the sandy loam site, with a significant quadratic effect evident for both nutrients.
Application of N and P also influenced crop lodging at both sites, but no effect of KCl on crop lodging was evident. At both sites, N application increased crop lodging overall; however, a significant N*P interaction was evident both at the clay loam site at crop heading, and at the sandy loam site at crop maturity. At the clay loam site, P application increased crop lodging in higher N treatments, but had no effect on lodging in lower N treatments. At the sandy loam site at crop maturity, P application resulted in a significant increase in lodging for the highest N treatment. Lodging was also assessed at the sandy loam site at the heading stage; however, lodging was minimal (averaging 1.8 on a scale of 1 to 9).
Biomass and Grain Yield
Application of N and P improved oat growth at both field sites in 2000, as measured by increased biomass and/or grain yield. No significant interactions among the nutrients applied were evident.
Nitrogen application increased biomass yield at tillering and at crop heading at both sites. This positive N response was also evident at crop maturity. At the sandy loam site, grain yield increased with N additions of up to 80 kg N ha-1 and, at the clay loam site, grain yield increased with N additions of up to 40 kg N ha-1. Additional N did not produce additional yield increases. At both sites, soil NO3--N levels were quite low, ranging from 20 to 27 kg NO3--N ha-1 to 60 cm in the fall prior to crop establishment.
Phosphorus application resulted in a significant increase in plant biomass yield at crop tillering at both sites. The addition of P also appeared to enhance the rate of early-season crop development, which may have contributed to improved early-season crop establishment and competitiveness (data not presented). Presumably, cool conditions early in the growing season combined with marginal soil P levels contributed to this marked early-season response to P. By the time of crop heading, effects of P application on biomass yield had disappeared at the sandy loam site; however, at the clay loam site, biomass yield at crop heading was found to increase linearly with increasing P rate. Despite positive effects of P application on early-season crop growth, P application had no effect on grain yield at either site suggesting that P was not a limiting factor in terms of grain yield.
The application of KCl did not have a significant effect on biomass or grain yield of oats at either site in 2000. However, KCl tended (P=0.06) to increase grain yield at the clay loam site. At both sites, the soil levels of K and Cl- were considered to be adequate to optimal.
Fertilization influenced various grain quality parameters. Overall, N application often appeared to have a negative effect on grain quality; effects of P and KCl on grain quality were comparatively less consistent. Significant interactions among fertilizer treatments were evident in a few cases, but generally not consistent between sites.
Nitrogen application reduced the percentage of plump kernels at both field sites, and also increased the percentage of thin kernels at the sandy loam site. Both percent dockage and the percent wild oats present in the grain sample were also influenced by N fertilization. At the clay loam site, N application resulted in a significant linear increase in both the percent dockage and the percent wild oats present in the grain sample while, at the sandy loam site, a higher percent dockage and a higher percentage of wild oats in the grain sample were associated with the highest rate of N applied.
Nitrogen alone, and in combination with other fertilizer treatments, also influenced kernel weight and test weight. At both sites, declines in kernel weight were associated with increasing N applications; however, at the sandy loam site, a statistically significant N*KCl was evident. Contrast analysis indicated that KCl caused a significant increase in kernel weight only at the N rate of 40 kg N ha-1. At both field sites, overall declines in test weight were also associated with increasing N rates; however, a statistically significant N*P interaction was evident at both sites. Contrast analysis revealed that, at the sandy loam site, P application increased or tended (P=0.07) to increase test weight at the low rates of N, but had no effect on test weight at high rates of N. In contrast, at the clay loam site, P application did not have a significant effect on test weight at low rates of N, but decreased test weight at high rates of N. Interestingly, P application increased crop lodging at the high rates of N at the clay loam site; however, the degree to which lodging may have contributed to decreased test weight is unclear.
Phosphorus application appeared to have minimal effects on grain quality. The addition of P reduced kernel weight at the clay loam site, and decreased the % dockage at the sandy loam site.
Application of KCl also appeared to have a smaller impact on grain quality than N application, but did result in an overall increase in the percentage of plump kernels and kernel weight at the clay loam site.