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Deep Placement Effects of Nitrogen and Phosphorus Grain Yield, Nutrient Uptake, and Forage Quality of Winter Wheat¹

Nitrogen and P applied together in deep-band applications have been reported to increase crop production over that obtained with conventional applications. Little information is available on the continuous use of this method of application. Therefore, the objective of this study was to compare the effects of N, P, and N plus P knifed in bands with conventional broadcast methods on grain yield, N and P uptake in grain, and concentration in wheat forage when applied several years at the same location. Winter wheat (Triticum aestivum L.) was grown at three locations from 1980 to 1983. Two N sources, anhydrous ammonia (AA) and ammonium nitrate (AN), one P source, ammonium polyphosphate (APP), and one nitrification inhibitor source, nitrapyrin (NI), were used. Rates of N, P and NI were 112, 30, and 0.56 kg ha^–1, respectively. Methods of N and P fertilization included broadcast (BC) and knifed (KF) in bands 15 cm deep with 45-cm spacings. Crops responded to N fertilization at Altus (southwest location), N plus Pat Stillwater (northcentral), and P at Haskell (northeast). Effects of methods of application varied with locations and years. The first year, at Stillwater was the only occurrence of N and P knifed in that resulted in higher yield and N and P uptake in grain compared with broadcast methods. However, with continued fertilization in the same plots with subsequent years, the positive effect of fertilizer in deep placed bands diminished, and broadcast applications were more efficient. Broadcast P applications were more efficient in later years of the study at Haskell where the greatest response to P fertilization was obtained. No long-term benefits due to placement of N and P together or in combination with NI in deep bands were observed at any of the three locations.

Key Words: Anhydrous ammonia • Ammonium nitrate • Ammonium polyphosphate • Nitrapyrin • Broadcast application • Dual placement • Triticum aestivum L.

² Professor and former senior agriculturist, Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078.

Received for publication October 30, 1984.