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The Magruder Plots: Untangling the Puzzle

Previously Published in Agron. J. 99:1191–1198 (2007)

Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078. Contribution from the Oklahoma Agricultural Experiment Station

^* Corresponding author (bill.raun{at}okstate.edu).

Long-term experiments play a vital role in revealing dynamic soil and weather processes that directly influence sustainable crop production and ecosystem health. The objective of this review paper is to present one of the oldest long-term continuous winter wheat (Triticum aestivum L.) experiments, the Magruder Plots, and their contribution to the scientific community regarding questions of yield response to amendments, yield stability, percentage organic matter (OM) lost over time, soil nutrient status, microbial activity, weed population, and information on the economic return from winter wheat production. Alexander C. Magruder initiated the experiment in 1892 and is in progress to date. The original plot was started to evaluate wheat production on native prairie soils without fertilization. After 6 yr the principal investigator split the initial plot into two and fertilized one half with cattle manure. The experiment was then modified to include 10 treatments in 1930 by Dr. Horace J. Harper to answer several soil fertility related questions. Since 1947, six treatments have remained intact that evaluate simple combinations of manure, and inorganic N, P, K, and lime. Following 114 yr of continuous winter wheat production under conventional tillage, the check plot that has never received any fertilizer addition continues to produce wheat grain yields of >1 Mg ha^–1. Despite the decline in soil organic matter from 4 to 1% during this time period, wheat grain yields continue to show slight increases with time, likely due to improved genetics. While continuous wheat without rotation is not recommended, this 114-yr study documents the feasibility.

Abbreviations: NPKL, superphosphate + sodium nitrate + potash + lime • OM, organic matter

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Received for publication January 4, 2007.