Soil water dynamics and dry‐matter production of old man saltbush‐, native grass‐ and lucerne‐based pastures in a variable summer‐dominant rainfall environment, Australia

Abstract

In a summer‐dominant high‐rainfall, yet seasonally dry environment, soil water dynamics and dry‐matter (DM) production were monitored during 2006–12, for three perennial pasture types: old man saltbush (Atriplex nummularia ssp. nummularia with native grass), native grass (Bothriochloa macra and Rytidosperma bipartita dominant) and lucerne (Medicago sativa cv. Venus). Plant root depth of the old man saltbush pasture (1·5 m) was greater than that of native grass (1·2 m), but equal to that of lucerne (1·5 m), resulting in equivalent levels of maximum extractable water (MEW; mm, 0–1·7 m) for saltbush and lucerne in five of the six seasons. Lucerne (MEW 242 mm) extracted more soil water than native grass (144 mm), but was similar to old man saltbush (205 mm). In the second year of growth, both the lucerne and old man saltbush pastures achieved their maximum yields of 16·8 and 7·9 t DM ha−1 respectively, but thereafter declined. The decline in yield of lucerne in later years was associated with a significantly lower plant frequency and increase in proportion of weeds. The decline in yield of old man saltbush appeared to be associated with an increasingly dry soil profile, despite receiving rainfall that was above average. The yield of the native grass pasture increased during the study as the proportion of weeds declined, and the presence of saltbush plants did not compromise the yield of perennial grasses in the inter‐row spaces. The implications of these findings for livestock production systems in this environment are discussed.

Soil water dynamics, herbage production and water use efficiency of three tropical grasses: Implications for use in a variable summer‐dominant rainfall environment, Australia

“…Preliminary findings for this study were previously reported for plant root depth (Murphy et al., 2008a), water use efficiency (Murphy et al., 2008b) and soil water dynamics of tropical grasses (Murphy, Lodge, Brennan et al., ) and saltbush‐based pastures (Murphy et al., ).…”

“…The climate of the region is typical of moist mid‐latitudes having a mild winter and hot humid summer (Köppen‐Geiger class Cfa—humid subtropical, Peel, Finlayson, & McMahon, ). Site characterization including exploratory soil coring, soil profile physical and chemical characteristics and establishment of treatments was reported by Murphy, Boschma, and Harden (). Briefly, soil surface texture was a silty loam and the B‐horizon at 0.3 m was silty clay loam–silty light clay with a mean maximum depth of 1.61 m. Bulk density increased with depth of soil with values ranging from 1.29 at the surface to 1.87 Mg/m 3 at 1.3–1.5 m, and bulk density was always <1.6 Mg/m 3 for soil layers shallower than 0.9 m. The plant available water capacity (PAWC), being the difference between profile SSW at drained upper limit (c. –10 kPa, 567 ± 26 mm) and crop lower limit (c. –1,500 kPa, 306 ± 29 mm) was 261 ± 3 mm (McKenzie & Cresswell, ; Murphy et al., ).…”

“…Site characterization including exploratory soil coring, soil profile physical and chemical characteristics and establishment of treatments was reported by Murphy, Boschma, and Harden (). Briefly, soil surface texture was a silty loam and the B‐horizon at 0.3 m was silty clay loam–silty light clay with a mean maximum depth of 1.61 m. Bulk density increased with depth of soil with values ranging from 1.29 at the surface to 1.87 Mg/m 3 at 1.3–1.5 m, and bulk density was always <1.6 Mg/m 3 for soil layers shallower than 0.9 m. The plant available water capacity (PAWC), being the difference between profile SSW at drained upper limit (c. –10 kPa, 567 ± 26 mm) and crop lower limit (c. –1,500 kPa, 306 ± 29 mm) was 261 ± 3 mm (McKenzie & Cresswell, ; Murphy et al., ). The soil profile was non‐saline throughout (<0.1 dS/m), and it showed a neutral pH trend with values being moderately acid at the soil surface (pH Ca 5.2), neutral at 1.0 m (pH Ca 7.2) and slightly alkaline at 1.6 m (pH Ca 7.9).…”

“…The experiment was a modified randomized complete block design with three replicates. Ten treatments were allocated randomly to plots (each 6 × 9 m) in each of three replicates (Murphy et al., ). This paper reports findings from eight of the treatments: (a) “native grass” consisting of a mix of native perennial grasses (redgrass; wallaby grass, Rytidosperma bipartita cv.…”

“…Complete details of the aluminium access tubes, installation and NMM calibration were reported by Murphy et al. (). Neutron counts were taken on 51 occasions from 6 December 2005 to 29 October 2008.…”