Research report from OSU's North Willamette Agricultural Research and Extension Center
Delbert Hemphill
OSU Dept of Horticulture, NWREC
John Hart
OSU Dept. of Crop and Soil Science
Introduction
Cauliflower is also planted at lower populations and with greater between-row spacing than is the norm for broccoli. The purpose of this trial was to study the response of cauliflower to several rates of applied N fertilizer and combinations of banded versus broadcast placement of both the initial and sidedressed fertilizer applications. A second purpose was to study soil N accumulation as a function of rate of applied N and presence of a winter catch crop, and to monitor movement of nitrate through the soil profile in the winter following the crop.
Methods
'Snowball Y' cauliflower was direct-seeded in a Willamette silt loam, pH 5.9, at the NWREC on 3 June. Rows were 12 inches apart with a plant density of about two/inch in the row. Plot preparation included a broadcast and incorporated application of 10N-8.7P-16.7K fertilizer at 600 pounds/acre, boron at 2.0 pounds/acre, trifluralin at 0.75 pounds/acre, and chlorpyrifos at 1.3 pounds/acre. On 14 July, the seedlings were lifted with a shovel and transplanted bare-root into their final location. Soil preparation was the same as for the seed bed. Transplants were set in rows 2.5 feet apart with 18 inches between plants in the row. Plot size was three rows, 20 feet long. All three rows were harvested. The initial application of 40 pounds N/acre, as urea, was either broadcast or banded 3 inches to the side and 2 inches deep immediately after transplanting and irrigated in. The remaining urea was broadcast or banded on the appropriate plots on 20 August (Table 1). Treatments were in randomized complete block design with four replications. The plots were sprinkler-irrigated as necessary and harvested on 29 September and 5 and 15 October. In addition to the combination of nitrogen rates and methods of fertilizer placement, one set of plots (treatment 12) was reserved for sequential sampling of shoot dry matter accumulation and N uptake. Another set of plots (treatment 11) received its initial N application in the form of 15N-enriched urea. These plots were harvested separately for refined determinations of N uptake. Two sets of plots (treatments 13 and 14) were interseeded with 'Wheeler' cereal rye on 3 September to determine the feasibility of overseeding in cauliflower as a means of establishing a winter N catch crop. Following the last harvest, soil in treatments 1, 2, 3, 4, 5, and 11 were sampled to 40-inch depth in 10-inch increments. The plots were maintained through the winter in order to resample for soil N content and cover crop biomass accumulation.
Results and Discussion
For the plots receiving only broadcast applications of urea, yield increased with increasing N rate to a maximum at 240 pounds/acre (Table 2). The same trend was true for mean head weight and the percentage of Grade No. 1 heads (defect-free). Previous work at the OSU vegetable farm suggested that the optimum rate of N application to cauliflower is in the range of 150 to 200 pounds/acre, somewhat lower than the results obtained in this trial.
Banded versus broadcast application of N at planting had no significant effect on yield or quality (Table 3), although there was a trend toward higher yield and head size with a banded application. Apparently, even with rows 30 inches apart, enough feeder roots establish in the soil between the rows that concentrating the fertilizer near the plant row is not a great advantage. This is in agreement with results obtained on broccoli grown on 16 or 20-inch row spacing.
Broadcast application of the sidedressed N resulted in significantly higher yield and mean head size than when the sidedressed N was banded. This was true at the 240 pounds/acre rate as well as the sub-optimal rate. The single greatest yield in this trial was with the combination of banded fertilizer at planting, broadcast sidedress fertilizer, and a rate of 240 pounds N/acre.
Overseeding cereal rye about four weeks before first harvest did not reduce cauliflower yield (Table 4). This is not surprising, as the stand of rye was sparse (approximately eight plants/square foot) and had not developed beyond the one-true leaf stage at harvest.
Results of soil tests for residual fertilizer after harvest, and for N uptake as a function of crop growth are not yet available. The soil and rye will be sampled in the spring as a function of rate of applied nitrogen to determine the amount of nitrogen leached versus that trapped in the rye shoots.
Table 1. List of treatments, 1992 cauliflower N utilization trial, NWREC No. Total N applied Placement at planting Placement at sidedress --------------------------lb/A---------------------------------- 1 0 0 0 2 80 40 broadcast 40 broadcast 3 160 40 broadcast 120 broadcast 4 240 40 broadcast 200 broadcast 5 80 40 banded 40 broadcast 6 240 40 banded 200 broadcast 7 80 40 broadcast 40 banded 8 240 40 broadcast 200 banded 9 80 40 banded 40 banded 10 240 40 banded 200 banded 11 160 40 broadcast-15N 120 broadcast-15N 12 160 40 broadcast 120 broadcast 13 80 40 broadcast 40 broadcast, overseed 14 240 40 broadcast 200 broadcast, overseed Table 2. Effect of rate of broadcast nitrogen on yield, head size, and quality of cauliflower, NWREC, 1992 N rate Mean head Grade No. 1 Total yield (lb/acre) wt. (g) heads (%) (tons/acre) 0 430 68.3 4.8 80 678 82.4 7.4 160 751 88.0 7.8 240 815 89.5 8.6 LSD (0.05) 186 10.6 2.2 Table 3. Effect of broadcast versus banded application of initial and sidedressed N on yield, head size, and quality of cauliflower, NWREC, 1992 Placement Placement N rate Mean head Grade No. 1 Total yield at planting at sidedress (lb/acre) wt. (g) heads (%) (tons/acre) Broadcast Broadcast 80 678 82.4 7.4 240 815 89.5 8.6 Mean 747 85.9 8.0 Banded 80 633 80.6 6.6 240 736 90.1 7.7 Mean 684 85.4 7.2 Banded Broadcast 80 727 86.2 7.0 240 1051 90.7 10.9 Mean 889 88.4 9.0 Banded 80 549 88.7 6.2 240 684 83.7 8.6 Mean 617 86.2 7.4 Broadcast at planting mean 716 85.7 7.6 Banded at planting mean 753 87.3 8.2 Significance, planting NS NS NS Broadcast at sidedress mean 818 87.2 8.5 Banded at sidedress mean 651 85.8 7.3 Significance, sidedress ** NS * Table 4. Effect of overseeding cereal rye on cauliflower yield, head size, and quality at two rates of nitrogen, NWREC, 1992 Treatment N rate Mean head Grade No. 1 Total yield (lb/acre) wt. (g) heads (%) (tons/acre) Overseeded 80 649 81.0 6.4 240 874 90.2 9.6 Mean 762 85.6 8.0 Not overseeded 80 678 82.4 7.4 240 815 89.5 8.6 Mean 747 86.0 8.0 Significance NS NS NS