RESULTS (Continued)

Similar to P, clipping K concentrations were also above the sufficiency level of 1.75% (Table 3) even when no K was applied (Table 1). Clipping K did increase somewhat with the application of K, but the increases in clipping K did not correspond completely with the amounts of K applied. For example, the same amounts of K were applied in the Spring Valley 12-1-12 and Natural Products Research 12-3-12, but clipping K in the two treatments differed by 0.15%.

There were no treatment differences in clipping concentrations of Ca, Mg, S, Fe, Mn, Zn, Cu, or B. Hence, these data are not being reported.

Clipping weights determined on July 11 and October 14 were highly variable within and between these dates (Table 4). Consequently, the LSD values calculated were very large and few treatment differences can be declared significant. Treatments with unusually low clipping weights on July 11 showed quite different growth rates in October. These results are perplexing and are taken as an indication that for 1997 methodology for measurement of fertilizer effects on bentgrass growth have to be modified.

Root mass was measured in October for five ¾-inch diameter by 6-inch long soil cores randomly removed from each plot. The values obtained ranged from 151 to 247 milligrams (Table 4). The only significant difference observed was between the highest and lowest root masses - 151 mg for the EXP 6200 and 247 mg for the Country Club 18-4-10 treatment. The latter is under-standable given the relatively low clipping weights obtained.

Soil microbiological activity was measured by trapping on soda-lime particles the carbon dioxide evolved when 20-g soil samples were moistened and placed in a closed container for 7 days. The results, expressed in terms of milligrams carbon dioxide evolved per square centimeter of soil surface area, are presented in Table 5. The data for May 21 precede any fertilizer application and indicate considerable natural variability in soil microbial activity. Statistically, some of the natural variation resulted in significant differences among the plots to which the treatments were assigned. This being the case, it is more logical to observe changes in microbiological activity than the actual values.

Between May 21 and August 8, the changes in microbiological activity ranged from a 2.60-mg reduction to a 5.16-mg increase in CO2 produced per centimeter squared of soil surface (Table 5). The largest reductions in microbial activity occurred in the EXP 1628 and Spring Valley 21-3-12 treatments while the largest increase was in the NPR 12-3-10 treatment. In general, microbial activity declined for those fertilizers with a natural organic base amended with synthetic N or K and increased for the all natural organic fertilizers. The sole exception was the Country Club 18-4-10, which registered an increase in microbial activity.

Between August 11 and September 17, fertilizer effects on soil microbial activity were highly variable (Table 5). Some of the fertilizers that reduced microbial activity between May and August increased activity from August to September while others showed consistent reductions in activity. The large gains in activity seen for some of the all natural organic fertilizers in July were often offset to a considerable extent by reductions in microbial activity between August 11and September 17.

In mid-August the plots became heavily infested with dollar spot. Visual estimates were made of the percentage of each plot covered by dollar spot prior to treatment with Daconil 2787. Plots with the lowest levels of infection were those receiving applications of the EXP 1628 and Natural Science 12-0-0 fertilizers (Table 6). The most heavily infected treatment was Creekwood 4-5-3. Only the infection rates between these lowest and highest levels were significant.

Thatch thickness measured in October showed minimal variation from treatment-to-treatment (Table 6). As a group, the experimental fertilizer plots tended to have less thatch than did the other treatments.

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