Regrowth of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) following defoliation

Effects of defoliation of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) on the amount of time required to reach peak regrowth, the lag period for regrowth to begin, regrowth biomass, tiller survival and replacement, and carryover effects of defoliation the following year were investigated. Regrowth of crested wheatgrass was determined during the summers of 1990, 1991 and 1992 in central Saskatchewan following a single defoliation to a 5-cm stubble height at eight stages of growth. Crested wheatgrass regrew 54–130 g m−2 of biomass when defoliated tillers had ≤3.6 leaves. Regrowth began accumulating within 3–53 growing degree-days (GDD) and peaked in 705–875 GDD. Rates of leaf development after defoliation (218–252 GDD phyllochron−1) equaled or were faster than control (218–330 GDD phyllochron−1). Regrowth biomass accounted for 35–76% of total annual production. Total annual production was greatest when plants were defoliated during vegetative growth or at peak growth. In 1991 and 1992, etiolated growth in the spring following defoliation was reduced by defoliation in the previous year. Tiller replacement was not affected by defoliation and averaged 1.2 tillers tiller−1 (SE = 0.1) in 1991 and 1.5 tillers tiller−1 (SE = 0.1) in 1992. Two periods of grazing can be expected from crested wheatgrass if it is grazed when tillers have ≤3.6 leaves; however, the impacts of a second grazing must be determined. If crested wheatgrass is grazed late in the growing season, only one period of grazing can be expected, and production will likely be less the following growing season, necessitating a rest period for plants to regain their production potential. Key words: Crested wheatgrass, defoliation, grazing management, growing degree-days, phyllochron, regrowth

Lessons from the South Auckland Winter milk monitoring programme, 1987-1997

The performance of winter milk production systems, represented by between 7 and 17 New Zealand Dairy Group suppliers in the South Auckland area, has been assessed for seven consecutive years. The monitoring programme has enabled comparison of winter milk systems with typical seasonal supply systems, and identification of management issues facing winter milkers. In 1995/ 96 the monitored farms had contract volumes ranging between 7 and 32 litres/ha (average 21 litres/ha). This reflected the total situation for all the NZDG winter milkers. Total annual production is also critical for profitability, and ranged between 684 and 1107 kg milksolids (MS)/ha in the year ending 31 August 1996 (mean 920 ± 144 kg MS/ha). The main requirements for successful winter milk production include planning and acting early for winter, in particular by: 1. early use of supplements in the autumn, including hay, silage and urea; 2. appropriate drying off of cows; and 3. grazing drystock off the home farm, so it can be effectively used as a milking platform. Keywords: dairying, farm monitoring, South Auckland, winter milk

Assessment of strains of Bradyrhizobium sp. (Lupinus) for serradellas (Ornithopus spp.)

Several strains of Bradyrhizobium sp. (Lupinus) were compared, in the glasshouse and field, with the Australian commercial inoculant strain, WU42.5, for symbiotic performance on serradella. Strains WSM471 and USDA3709 were more effective in nitrogen fixation (12 and 8% respectively) than WU42.5 across 10 serradella lines, although WU42.5 generally displayed good levels of effectiveness. WSM471 was a more saprophytically competent strain than WU425 in mildly acidic sandy soils, resulting in a 2.8-fold increase in the nodule score of serradella sown 32 cm from a line of bradyrhizobia established the previous year. Although WSM471, when compared with WU42.5, increased the nodulation and early production of an established sward of serradella, it did not improve total annual production of the sward. The possible replacement of WU42.5 with WSM471 in serradella inoculants is discussed.

Regrowth of smooth bromegrass (Bromus inermis Leyss.) following defoliation

Regrowth and production of tillers in smooth bromegrass (Bromus inermis Leyss.) following defoliation to a 5-cm stubble height were monitored throughout the summer and in early spring the following year in central Saskatchewan. After defoliation, while smooth bromegrass was vegetative, forage began accumulating in 45–75 growingdegree-days (GDD) when moisture was favorable. Regrowth ranged from 34 to 84 g m−2. Plants also produced ≤ 51 g m−2 of regrowth when defoliated at or before culm elongation in a year with above-average precipitation. In two dry years, regrowth was minimal and plants did not regrow after defoliation in the later vegetative growth stages; however, new leaves were produced within 110–140 GDD. Following defoliation at early vegetative growth stages, 1030–1180 GDD were needed to reach maximum regrowth. Total annual production was either unaffected or reduced by defoliation. Total annual production ranged from 35 to 139 g m−2, with yields lowest when defoliated in early May or early June and highest when herbage was removed in mid-May or near flowering and seed production. When plants were defoliated during vegetative growth most tillers were produced the following spring, whereas when plants were defoliated during reproductive phases the majority of tillers emerged in the fall. The year after defoliation, the density of tillers (871–951 m−2) was not significantly different among treatments. Regrowth following defoliation cannot be related to a particular growth stage, but rather it depends on growing conditions. If smooth bromegrass is defoliated once and rested until the next year, it should be recovered by early spring and its productivity should be unaffected. Key words: Etiolated growth, forage production, grazing management, regrowth, rest requirement, tillering

Trophic Linkage between Stream Centrarchids and Their Crayfish Prey

Energetic links between smallmouth bass (Micropterus dolomieu) and rock bass (Ambloplites rupestris) and their crayfish foods were examined in an Ozark stream. A trophic level energy budget was developed by enumerating food habits for different age (size) fish, estimating annual production for both fish and crayfish, and using laboratory- and literature-derived bioenergetic and gross efficiency data. Both fishes began life feeding on small invertebrates (mayflies and chironomids) but within 3 mo switched to a diet of mainly crayfish and Cyprinidae. Total annual production of smallmouth bass was 0.262 g dry weight∙m−2∙yr−1 (6344 J) and rock bass 0.148 g∙m−2∙yr−1 (3607 J). Total annual production of crayfish was 4.15 g dry weight∙m−2∙yr−1 (55 736 J) for Orconectes luteus and 5.05 g∙m−2∙yr−1 (62 394 J) for O. punctimanus. Only about half of the crayfish production was available to fish, due to size-selective predation and behavioral traits of the prey. A predator–prey model suggested that nearly one third of total crayfish production during their vulnerable period was lost to centrarchids, and that half of the existing biomass was consumed. Fish are probably the major cause of mortality in crayfish and undoubtedly influence crayfish population dynamics and energy flow through the river system.

Estimates of annual production for some aquatic insects from the La Trobe River, Victoria

Annual production was estimated by the size-frequency method for Ephemeroptera (Tasmanocoenis tonnoiri, two species of Baetis, Atalonella spp., Atulophlebioides sp.), Plecoptera (Leptoperla spp.) and Trichoptera (Ecnomus sp.) at four sites on the lowland section of the La Trobe River. Annual production (P) of individual ephemeropteran species (or genera) varied from 0.02 to 0.7 g m-2 while total annual production of this order at two sites was 0.7-1 . 5 g m-. Annual production of Leptoperla spp. was 0.03 g m-2 at one site while Ecnomus sp, averaged 2 g m-2 at two sites. Estimates of annual production were subject to an error of at least t 50%. Annual turnover ratios (P/B; B is mean biomass) varied from 9 to 19 and were three to four times higher than published values for similar-sized macroinvertebrates in the temperate zone (generally < 15°C mean annual habitat temperature). This probably resulted from the higher average temperatures (17-18°C) at most sites.

Annual Production by Caddisflies and Mayflies in a Western Minnesota Plains Stream

Annual production was estimated for five species of caddisflies and mayflies, comprising major components of the insect community, in the Redwood River, a second- to third-order plains stream in western Minnesota. Estmates were made at two sites, one above and one below an impoundment. At the upstream site, annual production (g∙m−2, wet weight) and annual P/B ratios (in parentheses) were Hydropsyche bifida, 8.3 (6.9); Cheumatopsyche pettiti, 5.5 (7.0); Stenonema nepotellum, 3.4 (5.7); Stenacron interpunctatum canadense, 0.8 (7.0); and Caenis simulans, 4.7 (4.2); with total annual production of 22.7 g∙m−2. At the downstream site, annual production and P/B ratios were H. bifida, 34.3 (4.4); C. pettiti, 68.5 (4.4); S. interpunctatum canadense, 24.1 (6.1); and C. simulans, 2.8 (4.4); with total annual production of 129.7 g∙m−2. These species comprised 27.5% of the total insect standing stock at the upstream site and 75.9% downstream. The hydropsychid production at the downstream site was apparently sustained by the drift of zooplankton from the impoundment, resulting in considerably higher production by hydropsychids than reported in woodland streams.Key words: production, Trichoptera, Ephemeroptera, plains stream, benthos, size–frequency method

Production and Movement of Juvenile Rainbow Trout (Salmo gairdneri) in a Headwater of Bothwell's Creek, Georgian Bay, Canada

Within the 21,500 m2 headwater, the standing population of juvenile rainbow trout reached a high of 7.05 g/m2 in October. Production was maximum during August at 1.77 g/m2. Total annual production is calculated at 284.5 kg (13.2 g/m2). Spring emigrants (no less than 4830 fish weighing 69 kg) were age I (91%) and age II. Minimum calculated ratio of production to yield as emigrants was 4.1:1. Comparatively few age 0 fish emigrated during summer. Because of their demonstrated capability to produce juveniles, sensitive headwaters must be preserved from ecological disturbance to assure self-perpetuating rainbow trout populations in the Great Lakes.