Nitrogen fixation in a white clover-grass pasture irrigated with saline groundwater

✍ Scribed by C. J. Smith; P. M. Chalk; C. L. Noble; J. B. Prendergast; F. Robertson

• Publisher: Springer
• Year: 1993
• Tongue: English
• Weight: 558 KB
• Volume: 13
• Category: Article
• ISSN: 0342-7188
• DOI: 10.1007/bf00190035

✦ Synopsis

Nitrogen (N2) fixation in an irrigated white clover-grass sward was estimated using the l SN isotope dilution technique following the addition of K 1SNOa at 0.5 gNm -2 and 80 atom % 15N in a field study during the 1990-91 season. Two water salinity treatments (channel water; ECw --0.07 and groundwater; 2.4 dS m-1) and four irrigation frequencies were included in a factorial design with four replicates. The channel water treatments were irrigated when pan evaporation minus rainfall equalled 50 mm, whereas the groundwater treatments were irrigated at deficits of 40, 50, 65 or 80 mm. Cumulative dry matter of the clover was significantly less in treatments irrigated with saline groundwater compared to channel water at day 164, and soil salinities (ECe) increased on average from 2.3 to 5.07 dS m-1. In contrast, salinity of the irrigation water had no effect on the cumulative yield of grass. Cumulative dry matter of the grass and clover were not affected by groundwater irrigation frequency. Total N accumulation by the grass did not differ significantly between treatments. However, total N accumulation in white clover was significantly less (P < 0.05) in all treatments irrigated with groundwater compared to channel water. Neither the N concentrations of the grass nor the clover differed significantly between the salinity treatments. Salinity and irrigation frequency had no effect on the proportion of clover N (Pat=) derived from N 2 fixation. The values of Pat= were high throughout, and increased progressively from 0.78 at day 39 to 0.91 at day 164 (P < 0.01). However, the yield of fixed N was lower in clover when watered with groundwater compared to channel water (P < 0.01). Thus low to moderate soil salinity did not affect the symbiotic dependence of clover, but the yield of biologically-fixed N was depressed through a reduction in the dry matter yield of the legume.