STEEP - Nitrogen Rates for Winter Wheat Grown in Different Rotations in Western Oregon

Lincoln Volker, James VanLeeuwen, and Helle and Bruce Ruddenklau
with Dost Mohammad Baloch and Russ Karow

Objective

To evaluate the nitrogen requirements of winter wheat grown after different rotation crops in western Oregon.

Grower, Location, Rotation Crop, N rate treatments

Grower	Location	Rotation Crop	Spring N rates lb/a	Wheat variety
Lincoln Volker	Monroe	sweet corn	0,50,10,150	Gene
James VanLeeuwen	Halsey	perennial grass	0,60,120,180	Gene
Ruddenklau	Amity	red clover	0,50,100,150	Gene

Comments

Wheat crops were established in fall 1994 and test plots were created in spring 1995 with single or multiple applications of nitrogen fertilizer at the late-tillering stage. Nitrogen was applied with field equipment in either liquid or dry form. Plots ranged in size from 24 to 42 feet wide and 300 to 500 feet long. Three replications were used at all locations. No lodging occurred in any of the replicated plots though lodging was observed in companion, higher rate, single replication plots. N rate differentials were visually obvious after heading. Winter precipitation was unusually high and nitrogen leaching likely occurred. Plots were combine harvested. Grain was weighed in a weigh wagon. Dost Mohammad Baloch, a PhD student in the OSU Dept. of Crop and Soil Science, is doing detailed nitrogen budgets for each of the sites.

Data

Conclusions

Wheat at all sites was responsive to nitrogen. Differences in wheat yield to the first two increments of nitrogen at the corn and clover sites were statistically significant while there were no statistical differences among N rates at the grass site (though yields continued to increase). Predictions on nitrogen need from the companion nitrogen budget study are shown at the bottom of table 1. Data for western Oregon indicates that 265 lbs. total N/a is needed to optimize yield. When predictions on nitrogen need are made in the spring, we assume needed nitrogen can come from four sources - that already present in the vegetation, nitrate in the soil, N mineralized from the soil and applied fertilizer N. The figures at the bottom of table 1 give the spring predicted N fertilizer need based on the measured N values. These studies will continue in 1995-96.

N rate	Corn Volker 50N	Clover Ruddenklau 50N	Grass VanLeeuwen 60N
		bu/a
0	78	74	48
1X	94	85	82
2X	113	92	87
3X	119	93	94
Average	101	86	78
PLSD (5%)	14	8	14
CV	7	5	9

4X	128	--	107
N need	265	265	265
Veg uptake	21	18	16
NO3	5	13	6
Min N	53	72	92
Est. Fert N	186	162	151