D. J. Barker

Vegetation diversity, growth, quality and decomposition in managed grasslands

The relationship between vegetation growth rate, quality, litter decomposition and diversity was investigated in four grazed grasslands differing in topography, management and fertility in the southern North Island of New Zealand. Vegetation samples were clipped at two sampling times (summer and autumn) from 0.5 m 2 areas excluded from grazing. Crude protein (CP), in vitro dry matter digestibility (IVDMD), neutral detergent fiber (NDF), average daily growth (ADG) rate, species composition and the relative extent of tissue degradation by soil microorganisms were determined for the vegetation samples. It was hypothesized that vegetation diversity would be negatively related with measures of vegetation growth, quality and decomposition. Comparisons made across all environmental and management conditions agreed with the hypotheses. Higher vegetation diversity was associated with lower ADG rate, lower CP concentrations, lower IVDMD and higher NDF concentrations. Comparisons within management regimes (MR), however, were less consistent and possible reasons for this are examined. Litter decomposition extent was closely related to the tissue quality characteristics of the vegetation, especially NDF concentration, but not species diversity. The observed local-scale relationships between the vegetation diversity, growth, quality and decomposition characteristics were contended to be largely the result of the influence of environmental resource richness on community structure of the managed grasslands studied. There is a need to promote a functionally diverse plant community over the entire managed area rather than promoting high localized species diversity within grasslands.

A practical model for predicting soil water deficit in New Zealand pastures

Abstract Soil water is the single most important resource for pasture and crop production in New Zealand farms. Because soil water is difficult to measure, however, the ability to predict soil water status from daily weather data is valuable, and has application for on‐farm irrigation, stocking, and supplementation decisions. In this paper a practical water balance model is presented. The model uses daily rainfall and potential evapotranspiration (PET) estimates to predict changes in the water content in two overlapping soil zones: a rapidly recharged (and depleted) zone of unspecified depth, and the total plant rooting zone. The use of two zones improves predictions of actual evapotranspiration and plant stress compared with models that use only one zone. An important factor determining the success of soil water models is the ability to predict actual evapotranspiration, AET. In this model actual evapotranspiration, AET, is calculated as the lesser of potential evapotranspiration, PET, and total readily available water (RAW) per day. RAW is defined as all of the water in the rapidly recharged surface zone plus a proportion of the water in the remainder of the soil profile. By validation against 11 historical data sets, the model is shown to give accurate predictions of soil water deficit across a range of New Zealand flat‐land pastoral soils. The model parameters can be easily estimated from commonly available soil properties (soil order classification, and available water holding capacity) without the need for additional site‐specific calibration. This model provides an easily used, practical decision tool for the management of drought, allowing early prediction of decline in pasture growth and estimates of required irrigation.

Pinitol accumulation in mature leaves of white clover in response to a water deficit

In this study, two genotypes from the white clover breeding line ‘Syrian selection’, which demonstrates improved survival in summer drought, and two from the white clover cultivar ‘Grasslands Kopu’, a more drought-sensitive cultivar, are compared in terms of their responses to a water deficit. Plants of each genotype were grown in a temperature-controlled glasshouse and a water deficit imposed through water deprivation. Proline content and the relative abundance of soluble carbohydrates were determined in mature leaf tissue excised from water-sufficient plants, from plants after a short-term period of water deprivation (prior to the onset of a significant change in leaf water potential (ct)) and from plants after a longer period of water deprivation (after a significant change in ct). Proline accumulated in concert with the onset of a significant change in ct; the highest content of 2.7 mg:g FW being measured in the Syrian selection genotypes compared with 2.4 mg:g FW measured in Kopu. In water-sufficient leaf tissue, pinitol was the major soluble carbohydrate present, with a significantly higher content (p 0.027) in terms of relative abundance in the Syrian selection genotypes when compared with the Kopu genotypes. After short-term water deprivation, pinitol was again an abundant soluble carbohydrate but the proportion of sucrose (in the Syrian selection genotypes) and fructose (in the Kopu genotypes) had increased to comprise significant levels in the leaf tissue. After a longer period of water deprivation, pinitol was again the major sugar present and represented a significantly higher proportion of leaf soluble carbohydrate (p 0.003) in the Kopu genotypes when compared with the Syrian selection genotypes. The results show that pinitol is the major soluble sugar present in mature leaves of white clover when subjected to a significant water deficit.

Morphological and physiological effects of water deficit and endophyte infection on contrasting tall fescue cultivars

Abstract Morphological and physiological responses to water deficit of two tall fescue (Festuca arundinacea) cultivars were compared in a glasshouse experiment and the effect, on those responses, of artificial infection of the tall fescue plants with two fungal endophyte (Neotyphodium coenophialum) strains was evaluated. The cultivars were Maris Kasba (MK), of Mediterranean origin, and El Palenque (EP), an Argentinian cultivar of temperate origin. The endophyte strains AgResearch isolate (AR501) and the Kentucky (KY31) wild type were compared with nil‐endophyte controls. Leaf growth rate of EP plants under water deficit was higher and leaf senescence rate lower than for MK plants (P < 0.05). MK plants showed a greater increase in the proportion of dead leaf tissue than EP plants as water deficit increased (P < 0.05). Stomatal conductance and lamina osmotic adjustment at low soil moisture were lower for MK than EP (P < 0.05). Endophyte‐infected plants had a lower dry weight and tiller number, but a higher net growth rate during water deficit treatments than endophyte‐free plants (P < 0.05). A significant cultivar × endophyte interaction (P < 0.05) was observed for many variables studied. This implies that any new endophyte strain should be evaluated in combination with the plant genotypes with which it is likely to be associated in commercial practice. MK‐KY31 and EP‐AR501 associations appeared to tolerate short‐term water deficit more effectively than other associations studied. There was evidence that the two endophyte strains studied had different physiological effects on their tall fescue host plants.

Effects of water deficit on Mediterranean and temperate cultivars of tall fescue

Two glasshouse experiments were carried out to evaluate the morphological and physiological responses to water deficit of Mediterranean and temperate tall fescue (Festuca arundinacea Schreb.) cultivars. In Expt 1, 3 cultivars were studied: 2 temperate cultivars, Grasslands Advance (GA) and El Palenque (EP); and a Mediterranean cultivar, Maris Kasba (MK). Water deficit was induced in containers of 4 plants of a single cultivar by withholding water. In Expt 2, plants of EP and MK were grown together in the same container and received water daily with gradation in intensity of water deficit achieved by varying the daily water ration per container. All cultivars in each experiment exhibited commonly reported responses to water deficit, characterised by diminished evaporative surface area and increased root : shoot ratio. The response of MK was primarily morphological and MK plants had smaller plant size, higher root : shoot ratio, and a lower growth rate compared with temperate cultivars. By contrast, response of temperate cultivars was primarily physiological; stomatal conductance of temperate cultivars was lower and these cultivars had a greater tendency for leaf lamina osmotic adjustment than MK under the most stressful water deficit conditions studied. The morphological adaptations of MK were very effective in delaying the onset of water deficit in Expt 1 when plants were grown with others of the same cultivar, but rendered MK plants uncompetitive and more susceptible to water deficit in Expt 2 where plants of MK where interspersed with plants of a temperate cultivar.

Influence of pastoral fallow on plant root growth and soil physical and chemical characteristics in a hill pasture

Pastoral fallowing over a growing season (October–May) has a profound effect on standing biomass and sward structure, and should have an impact on below ground plant growth and soil biological activities. Two field studies were conducted to compare the effects of pastoral fallow with rotational grazing on root growth and soil physical and chemical properties. Root growth and distribution was altered by pastoral fallowing and there was significantly (P < 0.01) less root biomass at 0–50 mm depth of soil in the fallowed sward than the grazed sward. Compared with the grazed treatment, pastoral fallow increased soil air permeability at 500 mm tension by 38%, saturated hydraulic conductivity by 26%, unsaturated hydraulic conductivity at 20 mm tension by 67% and soil moisture by 10–15%, and reduced soil bulk density by 11%. Fallowing had little effect on soil nutrients both at the end of fallowing, except for small reductions in K and Mineral N levels at 0–75 mm soil depth, and two to three years after fallowing.

Oversowing 'Grasslands Wana' cocksfoot, 'Grasslands Maru' phalaris, and 'Grasslands Tahora' white clover in hill country at varying rates of paraquat and glyphosate.

Abstract The influence of six pre-sowing herbicide treatments (no spray, two rates of glyphosate, and three rates of paraquat) on oversowing success of three species (‘Grasslands Wana’ cocksfoot, ‘Grasslands Maru’ phalaris, and ‘Grasslands Tahora’ white clover) were compared in autumn at two southern Hawkes Bay hill country sites (Ballantrae and Dannevirke) and in two seasons (spring and autumn) at the Ballantrae site. Pasture suppression by herbicide was compared using point analysis. Initial results from oversowing were compared by regular counts of seedling appearance and long-term results were determined from the contribution of introduced species to total herbage accumulation (HA) during the following 3-4 years. Paraquat and glyphosate were similar, at equal rates of active ingredient, for the establishment and performance of Wana or Maru, and were best at the highest rate of 0.7-D.8 kg a.i./ha. The contribution of Wana increased over 3 years under continuous sheep grazing to be 13-27% of total HA d...

Introduction, production, and persistence of five grass species in dry hill country: 8. Summary and conclusions

The production and persistence of five oversown grass species and resident pasture, were measured between 1979 and 1987 at six New Zealand sites, under several fertiliser (phosphate and/ or nitrogen (N)) and summer grazing severity treatments. ‘Grasslands Nui’ ryegrass (Lolium perenne L.), ‘Grasslands Wana’ cocksfoot (Dactylis glomerata L.) (‘Grasslands Apanui’ at Tekapo), ‘Grasslands Maru’ phalaris (Phalaris aquatica L.), ‘Grasslands Matua’ prairie grass (Bromus willdenowii Kunth), and ‘Grasslands Roa’ tall fescue (Festuca arundinacea Schreb.), established successfully at most sites. Findlay-Wilkinson analysis of annual total herbage accumulation (THA) of four sites, found that Maru production was above average and resident production was below average. Variation in THA between sites and years was related to variation in annual rainfall (621–1484 mm/ year). Wana was the most persistent grass at all sites (60% of THA after 4–6 years), followed by Nui (51% of THA after 4–6 years). Maru was only pe...

Introduction, production, and persistence of five grass species in dry hill country: 5. Central Wairarapa, North Island, New Zealand

A trial was conducted on a seasonally dry slope near Taupo as part of a national series investigating the persistence and productivity in dry hill country of five grass species established from oversowing under contrasting nitrogen (N) and summer grazing regimes. The average annual total herbage accumulation (HA) (1983–87) was greatest from phalaris (Phalaris aquatica L. ‘Grasslands Maru’) swards (12100 kg DM/ha, 65% Maru); followed by a species mixture (11700 kg DM/ha); tall fescue (Festuca arundinacea Schreb. ‘Grasslands Roa’) (11700 kg DM/ha, 47% Roa); prairie grass (Bromus willdenowii Kunth ‘Grasslands Matua’) (11300 kg DM/ha, 25% Matua); cocksfoot (Dactylis glomerata L. ‘Grasslands Wana’) (11100 kg DM/ha, 56% cocksfoot); resident swards (10640 kg DM/ha); and was least from ryegrass (Lolium perenne L. ‘Grasslands Nui’) (10200 kg DM/ha, 73% ryegrass). The average response from a split application of 50 kg N/ha in each of autumn and spring, was a 14% increase in annual HA. Summer grazing treatm...

Morphogenetic adaptation to defoliation and soil fertility in perennial ryegrass (Lolium perenne)

Abstract Morphogenetic adaptation, plasticity, and mortality of four perennial ryegrass populations, representing different selection histories, were compared in response to soil fertility and to defoliation severity. In a second experiment, morphogenetic adaptation and plasticity in response to defoliation frequency were studied in two divergent sub‐populations. Genetic variability was found between ryegrass populations for leaf appearance and elongation rates, leaf size, and tiller number. All populations exhibited plasticity in response to defoliation severity and soil fertility. There was no genetic variation for plasticity, the morphological response to the environment. Morphogenetic differences between populations remained constant across environments and resulted in differential mortality under the most severe defoliation. Both leaf length and rate of leaf appearance were positively correlated with greater mortality. The ryegrass ideotype for hill country is a compromise between yield and persistence.