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Effect of Sulfur Fertilization oil Three Annual Range Species I. Laughlin Soil Experiment¹

The fate of a single application of sodium sulfate and its effect on three range species grown alone and in pairs in free-draining lysimeters containing Laughlin loam soil (fine-loamy, mixed, mesic Ultic Haploxerolls) was monitored during two growing seasons. Plant growth responses to added S were small because the soil released considerable S during the course of the experiment, equivalent to more than half of the S application. However, the growth of subclover (Trifolium subterraneum L.) and its mixtures with fllaree [Erodium botrys (Cav.) Bertol.] and soft chess (Bromus mollis L.) was increased by S fertilization (P = 0.06). The botanical composition shifted towards subclover with added S. On the lysimeters where S was applied, subclover and filaree obtained more of their S from the applied fertilizer (55 and 55%) than did soft chess (44%). Total plant recovery of fertilizer sulfur in the 1st year was greater in pure stands of subclover (20%) than for soft chess (11 %) and filaree (7%). Total sulfur uptake was greatest on S fertilized lysimeters of subclover or sublover plus filaree. Leachate losses of S in the 1st year were positively related to the amount of S applied and volume of leachate and negatively related to S uptake by the plants. In the 2nd year leachate losses of S were positively related to the calculated S status of the soil at the end of the 1st year and negatively to plant S uptake. A greater leachate volume was lost from lysimeters containing filaree than containing soft chess or subterranean clover, and mixtures were intermediate. Leachate volume was not related to dry matter production. Sulfur application did not affect N uptake by the nonlegumes, but subclover N₂ fixation was increased by 60% during the 1st year. The percentage of subclover N coming from N₂ fixation was enhanced by the presence of nonlegumes. Estimates of recovery of fertilizer S were significantly less by calculations based on ³⁵S and than on total S differences suggesting that the labile ³⁵S is diluted in the soil solution by the release of nonlabeled S from decomposition of organic matter.

Key Words: Sulfur uptake • Sulfur leachate losses • Subclover (Trifolium subterraneum L.) • Soft chess (Bromus mollis L.) • Filaree [Erodium botrys (Cav.) Bertol.] • Nitrogen fixation • Nitrogen uptake

² Research assistant, agronomist, professor, and postgraduate researcher, Dep. of Agronomy and Range Science, Univ. of California, Davis.

Received for publication March 8, 1982.