Mixed Prairie vegetation in fair condition was fertilized with various rates of P, N, and NP. Rates of application by an increasing-rate spreader were: low, 10–185 kg/ha N, 10–155 kg/ha P; medium, 375–705 kg/ha N, 300–550 kg/ha P; and high, 870–1095 kg/ha N, and 680–820 kg/ha P. Total yield increased as a result of all fertilizer treatments. Palatability of fertilized vegetation was increased. Character of vegetation, unchanged by low rates, was changed by medium and high rates of N and NP. Bouteloua gracilis (HBK.) Lag., Stipa comata Trin. and Rupr., Koeleria cristata (L.) Pers., and Selaginella densa Rydb. decreased; Agropyron smithii Rydb., A. dasystachyum (Hook.) Scribn., and Artemisia frigida Willd. increased; and fertilized plots were invaded by Descurainia sophia (L.) Webb, Chenopodium leptophyllum Nutt., and Hordeum jubatum L. Fertilizer application increased rangeland production by about 300% at low rates and about 900% at high rates; the latter were accompanied by major vegetation changes. Since long-term effects of vegetation changes are unknown, only low rates of fertilizer application, which had little effect on the vegetation, can be recommended.
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Johnston et al. (1967) studied this question.