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Nitrogen cycling in tallgrass prairie was studied by using nitrogen content and concentration data for various ecosystem components on grazed and ungrazed tallgrass prairie in northeast Oklahoma. The seasonal dynamics of N in various plant parts was described, and the annual flow of N among different compartments was calculated. A simulation model was used to study the effect of grazing, fertilization, irrigation, and fire on nitrogen cycling. The results show that grazing, fertilization, and irrigation increase the nitrogen cycling rates. Annual spring fires reduce plant uptake and mineralization of N from plant parts, while mineralization of N from organic matter is increased.

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Dimension analysis was used to estimate biomass and annual net primary production for a post oak—blackjack oak (Quercus stellata—Q. marilandica) forest in central Oklahoma. Concentrations of six mineral elements in various plant tissues were determined and used with biomass and production estimates to calculate the annual cycle of N, P, K, Ca, Mg, and Mn in the forest. Total organic material in the forest is 245,000 kg/ha, of which 1.6% is leaves, 26.4% live branches, 5.9% dead branches, 44.8% trunks, 15.9% roots, 9.6% understory, and 4.4% litter. Annual net primary production is 14,900 kg/ha, distributed as follows: 32.0% leaves, 28.0% twigs and branches, 24.9% trunks, 15.1% roots, and 2.0% understory. Maximum leaf area index was 4.8. Yearly mean litterfall is 5,400 kg/ha and is distinctly biomodal, with peaks in November and March. The biomass contains 1,157 kg/ha N, 101 kg/ha P, 1,258 kg/ha K, 4,549 kg/ha Ca, 311 kg/ha Mg, and 124 kg/ha Mn. Yearly mineral budgets were determined for the six elements. Unusually high values for Ca in the biomass and in the mineral cycle were due to high concentrations of Ca in post oak bark (90,200 mg/g). High annual values for increment of biomass and for retention of mineral elements indicate that the stand has not reached a steady state, a conclusion that is confirmed by observations of stand structure.