Dt. Westermann et Se. Crothers, NITROGEN-FERTILIZATION OF WHEAT NO-TILL PLANTED IN ALFALFA STUBBLE, Journal of production agriculture, 6(3), 1993, pp. 404-408
Conservation tillage practices significantly reduce soil erosion, impr
ove water distribution, and decrease environmental concerns in furrow-
irrigated fields. Developing optimum N fertilization practices after l
egumes in these systems will help their adoption. We conducted three f
ield studies on a silt loam soil to determine if N fertilizer is requi
red for furrow-irrigated wheat (Triticum aestivum L.) planted in herbi
cide killed alfalfa (Medicago sativa L.) stubble. Fall regrowth of alf
alfa was sprayed with a mixture of 1 qt glyphosphate and 2 qt 2,4-D/ac
re. 'Stephens', a soft white winter wheat was planted with a double di
sk opener drill in two experiments and 'Bronze Chief', a hard red spri
ng wheat in a third experiment. Nitrogen fertilizer (ammonium nitrate)
was spring broadcast at four rates from 0 to 200 or 240 lb N/acre. Th
e buried plastic bag technique estimated available N (EAN); above grou
nd whole plant samples estimated root zone nitrate-N; and grain plot y
ields estimated with a combine. Nitrogen fertilization increased grain
yield in all experiments because sufficient N had not mineralized fro
m soil and legume residues before uptake needs of the wheat. The wheat
plant at the soft dough growth stage contained about 109 lb N/acre fr
om N mineralized from soil and legume residue sources. The apparent N
fertilizer recovery calculated by a combined regression relationship b
etween N uptake and fertilizer rates was 76%. The average plant recove
ry of mineralized N at maximum grain yields was calculated at 78%. Cro
ps planted in herbicide killed alfalfa should be selected so sufficien
t nitrate-N can accumulate from mineralization before maximum crop upt
ake and for N uptake ability in late summer. Nitrogen fertilizer appli
cations should be based on a spring soil test for nitrate-N in this no
-till system. Both practices will reduce the potential for nitrate-N l
eaching losses.