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Seeding Rates for Winter Rapeseed

Test seeding rate response of winter rapeseed, from 2 to 12 lb/A rates.

Location: Genesee, ID
Annual precipitation: 22 inches
Soil: Palouse
Rotation: 93 fallow

2, 4, 6, 8, 10, and 12 lb/A of rapeseed

One hundred lb N/A as anhydrous was applied in spring 93 before summer fallow. Rapeseed (Dwarf Essex) was planted 18 Aug 93 with an 8 ft drill. Each plot was 16' wide and 600' long. Stand counts were taken in fall and spring. There was no winterkill. A topdress of 50 lb N/A was applied 1 April 94. Plot borders were sprayed with Roundup to make 14.5 ft plots on 1 May 94. Parathion for seedpod weevil was applied 10 June 94. An International 453 with 16 ft header and weigh wagon was used at harvest.

There were no herbicides applied and no weed problems. Visually, the number of pods was similar between treatments although you could see that there were fewer plants in the low seed rate treatments.

Yield, lb/ac

Treatment	Rep 1	Rep 2	Rep 3	Rep 4	Rep 5	Average
2 lb	2360	2323	2586	3017	2790	2615a
4 lb	2314	2223	2459	2586	2786	2474a
6 lb	2314	2428	2223	2496	2723	2437a
8 lb	2223	2423	2450	2269	2859	2445a
10 lb	2087	2087	2087	2496	2586	2269a
12 lb	2133	2178	2360	2450	2477	2320a
LSD (5%)						178
CV						5.5%

Fall stand count, 1000 plants per ac

Treatment	Rep 1	Rep 2	Rep 3	Rep 4	Rep 5	Average
2 lb	142	133	145	139	145	141a
4 lb	244	218	221	196	207	217b
6 lb	312	400	332	340	318	340c
8 lb	394	360	397	437	474	412d
10 lb	479	522	505	383	454	468d
12 lb	559	542	505	462	717	557e
LSD (5%)						68
CV						14.4%

Conclusion

This large scale evaluation of seeding rate successfully validates information generated in small plots on seeding rate. From this trial and other trials I am confident that a grower using a seeding rate of 2 to 4 lb/A of live seed will have the potential of higher yields than at the higher seeding rates. This will be true under good seeding conditions that lead to uniform establishment of vigorous plants. The only other potential problem with low seeding rate is plant competition for weed control. In this experiment, no herbicide was applied except between plots in a 3.5' gap, and no weed problems were found anytime throughout the growing season. This system of validation of small plot results with large strips should be a valuable tool for researchers.

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU