M. B. Dodd

Effects of variation in shade level, shade duration and light quality on perennial pastures

Abstract Two experiments examining the effect of artificial shade on pasture net herbage accumulation (NHA), botanical composition and soil characteristics were conducted between 1994 and 1999 at Whatawhata Research Centre. Both experiments included a range of shade levels (0–94%) and shade durations (3–12 months per year). Experiment 1 also included a light quality treatment, incorporating a range in the red:far red ratio (0.49–1.00). All three shading factors decreased annual NHA, with the most influential being the level of shade, which accounted for 68% of the variation and reduced NHA by 20–80% compared with open pasture. The second most influential factor was shade duration, which accounted for only 6% of the variation in NHA. Shading also led to changes in pasture botanical composition, most notably a decline in legume content in both experiments. There was no evidence that hairy pasture species (grasses or legumes) had any advantage over glabrous species under shade. At shade levels >60%, herbage nitrogen concentrations were elevated by 0.2 percentage points on a per unit dry weight basis, although reduced pasture NHA under higher shading meant lower demand for soil nitrogen. Potential nitrogen mineralisation measurements also indicated that nitrogen cycling is likely to be reduced under shading.

Seasonal growth, phosphate response, and drought tolerance of 11 perennial legume species grown in a hill‐country soil

Abstract An experiment was conducted to evaluate 11 species (16 accessions) of herbaceous perennial legumes for their seasonal growth, response to added phosphate (P), and drought tolerance. Different species, and accessions of species, of the genii Adesmia, Medicago, and Trifolium were included. The plants were grown outdoors over 17 months in large (250 mm diameter) undisturbed hill‐country soil cores to provide full expression of their growth habit. Four rates of P were applied to the cores i.e. 0, 0.08, 0.24, and 0.48 g P/core. Herbage growth, stolon extension, and flowering patterns over 8 months were measured, after which the plants were subjected to a simulated summer drought and assessed for stress tolerance and recovery. The accessions showing the greatest growth rate throughout the year included two of T. pratense (Enterprise and a prostrate line); Huia white clover; and the South American legume Adesmia bicolor. The unnamed T. pratense line, and the Adesmia showed particular potential for stron...

Seasonal growth, flowering patterns, and phosphate response of 18 annual legume species grown in a hill‐country soil

Abstract An experiment was conducted to evaluate 18 herbaceous annual legume species for growth in a low‐fertility, low‐pH, hill soil, and for their response to added phosphate (P) fertiliser. Lotus, Ornithopus, Medicago, and Trifolium species were included. The plants were grown outdoors in large (250 mm diameter) undisturbed soil cores to provide for full expression of their growth habit. Two P treatments were applied to the cores, a zero rate and a high rate equivalent to 100 kg P/ha. Herbage growth, flowering pattern, and seed production over 8 months were measured. Ornithopus compressus and O. sativus had the highest growth rates and seed production, followed by Lotus subbiflorus and L. angustissimus. These four lines should be evaluated further under field conditions. A number of other species were unable to express full reproductive development under the harvesting regime imposed. A wide range in response to added P was recorded, Trifolium tembense having the greatest proportional increase in growth.

Development of subterranean clover (Trifolium subterraneum L.) genotypes for New Zealand pastures 1. Whatawhata persistence evaluation

Abstract A 2‐year trial evaluated the herbage production of a number of selected subterranean clover (Trifolium subterraneum L.) cultivars and lines. Seedlings were transplanted into small plots on a cultivated area of less than 5° slope. Morphological characteristics, spring herbage production, isoflavone content, and summer/autumn seedling emergence were measured. Of the cultivars evaluated in this trial, only ‘Denmark’ proved to be an improvement on ‘Tallarook’, and this was only on the basis of early‐season growth. However, a number of lines in this trial stood out in terms of their growth during the spring period and their high level of seed production. They included AK 664, WS 1436, and WS 536. Herbage harvested over 3 months from pure swards exceeded the equivalent of 2700 kg DM/ha, and seed production exceeded 7000 seeds/m2. These lines also had tissue formononetin levels less than 0.20% of dry weight. These results will be combined with those from previous persistence trials to determine those li...

Soil aluminium, phosphate, and moisture interactions affecting the growth of four white clover (Trifolium repens L.) lines

Abstract A glasshouse pot experiment using a yellow-brown earth hill-country soil was conducted over 14 weeks during autumn 1988. The objective of the trial was to determine the effects of differing levels of soil aluminium (AI), phosphate, and moisture (alone and in combination) on four white clover lines, i.e. ‘Grasslands Huia’, ‘G. Tahora’, ‘Prop’, and a selection from hill country in China. Plant growth, morphology, and nutrient content were measured. Decreased growth as a result of Al toxicity was exacerbated under conditions of low soil phosphate, and responsiveness to added phosphate was diminished under moisture stress. No AI by moisture interaction was observed. Although Huia attained the greatest yields under most conditions, it was less responsive to added phosphate than other lines, and was less tolerant of high soil AI than Tahora. Morphological differences between the lines were not affected by the treatments.

Does re-vegetating poor-performing patches in agricultural fields improve ecosystem function in the northern sandplain of the Western Australian wheatbelt?

There is an impetus to re-vegetate components of the Western Australian wheatbelt to address salinity and improve ecosystem function. In this study we use precision agriculture (PA) technologies and other methods to identify poor-performing patches for three farms, using historical yield maps to assess the ecological value associated with their potential re-vegetation. We also investigate how these patches changed with varying definitions of poor performance. Overall, poor-performing patches were rare and occupied 11.3, 13.5, and 25.3% of farmland across three farms, using the most aggressive definition of poor performance, which included the greatest proportion of arable land. We subsequently assessed the effect that re-vegetating these patches had on a suite of landscape metrics quantifying ecological value. On two farms, mean patch sizes were less than 1.2 ha for all definitions of poor performance. On the third farm, mean patch size increased from 0.9 ha to 2.6 ha as the definition of poor crop performance was altered to include more arable land. Patches were generally small and dispersed, did not significantly enhance connectivity in the landscape, and were therefore of limited ecological value. In general, re-vegetating poor-performing patches alone will provide little ecological benefit when re-vegetation is restricted to unproductive land. The ecological value of re-vegetation strategies in this landscape will improve only if some additional productive agricultural land is also taken out of production and re-vegetated.

Improving the economic and environmental performance of a New Zealand hill country farm catchment: 3. Short‐term outcomes of land‐use change

Abstract The third phase of a multi‐stakeholder, integrated catchment management project at the Whatawhata Research Centre is described. Land use and management changes were implemented to improve economic and environmental performance of the Mangaotama case study catchment farm. The major changes included: afforestation of 160 of the 296 ha catchment farm with pine and native trees, riparian management of the entire 20 km of stream network via fencing and/or forestry, restoration of 5 ha of existing native forest, and intensification of the remaining pastoral component to a high fecundity ewe flock and bull beef finishing. Marked improvements were observed in the key environmental and economic performance indicators. In particular, declines in sediment (76%) and phosphorus (62%) loads and faecal coliform (43%) levels were observed, native forest fragments showed early signs of recovery in terms of sapling numbers and vegetative cover, and the pastoral enterprise recorded increased per hectare production of lamb (87%) and beef (170%). There were implementation challenges with the better matching of land use to land capability, but this study demonstrated that significant progress can be made in the short‐term.

Improving the economic and environmental performance of a New Zealand hill country farm catchment: 1. Goal development and assessment of current performance

Abstract A multi‐stakeholder group including land managers, policy agencies and biophysical scientists was establishedto oversee a catchment scale project examining the economic and environmental performance of a representative North Island hill country catchment (296 ha Mangaotama catchment, Whatawhata) in the western Waikato region of New Zealand. The group first identified goals relevant to achieving a “well managed rural hill catchment”, including viable businesses, healthy ecosystems, protected landscape values, active partnerships, demonstrable environmental performance, and adequate rural services and infrastructure. The current state of the case study catchment was characterized by collecting data on key indicators chosen by the group to assess business viability and ecosystem health. Data included land use capability, vegetation cover, soil fertility, erosion, water quality, aquatic fauna, plant growth, terrestrial biodiversity, livestock enterprise performance, and economic farm surplus. The results were compared with a range of benchmarks, including adjacent catchments in different land use (water quality, biodiversity) and with hill country pastoral sector survey data (livestock performance and profitability). This comparison demonstrated that from both economic and environmental points of view, the catchment farm system was failing to meet the goals set by the management group. That result provided the impetus for the investigation of ways to improve performance.

Nitrogen Cycling from Increased Soil Organic Carbon Contributes Both Positively and Negatively to Ecosystem Services in Wheat Agro-Ecosystems

Soil organic carbon (SOC) is an important and manageable property of soils that impacts on multiple ecosystem services through its effect on soil processes such as nitrogen (N) cycling and soil physical properties. There is considerable interest in increasing SOC concentration in agro-ecosystems worldwide. In some agro-ecosystems, increased SOC has been found to enhance the provision of ecosystem services such as the provision of food. However, increased SOC may increase the environmental footprint of some agro-ecosystems, for example by increasing nitrous oxide emissions. Given this uncertainty, progress is needed in quantifying the impact of increased SOC concentration on agro-ecosystems. Increased SOC concentration affects both N cycling and soil physical properties (i.e., water holding capacity). Thus, the aim of this study was to quantify the contribution, both positive and negative, of increased SOC concentration on ecosystem services provided by wheat agro-ecosystems. We used the Agricultural Production Systems sIMulator (APSIM) to represent the effect of increased SOC concentration on N cycling and soil physical properties, and used model outputs as proxies for multiple ecosystem services from wheat production agro-ecosystems at seven locations around the world. Under increased SOC, we found that N cycling had a larger effect on a range of ecosystem services (food provision, filtering of N, and nitrous oxide regulation) than soil physical properties. We predicted that food provision in these agro-ecosystems could be significantly increased by increased SOC concentration when N supply is limiting. Conversely, we predicted no significant benefit to food production from increasing SOC when soil N supply (from fertiliser and soil N stocks) is not limiting. The effect of increasing SOC on N cycling also led to significantly higher nitrous oxide emissions, although the relative increase was small. We also found that N losses via deep drainage were minimally affected by increased SOC in the dryland agro-ecosystems studied, but increased in the irrigated agro-ecosystem. Therefore, we show that under increased SOC concentration, N cycling contributes both positively and negatively to ecosystem services depending on supply, while the effects on soil physical properties are negligible.

Process-based modelling to understand the impact of ryegrass diversity on production and leaching from grazed grass-clover dairy pastures

Abstract. Ecological studies often suggest that natural grasslands with high species diversity will grow more biomass and leach less nitrogen (N). If this diversity effect also applies to fertilised and irrigated pastures with controlled removal of herbage, it might be exploited to design pastures that can assist the dairy industry to maintain production while reducing N leaching losses. The purpose of this study was to test whether pasture mixtures with a high functional diversity in ryegrass traits will confer on the system higher water- and N-use efficiency. The hypothesis was tested using a process-based model in which pasture mixtures were created with varying levels of diversity in ryegrass traits likely to affect pasture growth. Those traits were: the winter- or summer-dominance of growth, the ability of the plant to intercept radiation at low pasture mass, and rooting depth. Pasture production, leaching and water- and N-use efficiency were simulated for management typical of a dairy pasture. We found that the performance of the diverse ryegrass–clover mixtures was more strongly associated with the performance of the individual components than with the diversity across the components. Diverse pasture mixtures may confer other benefits, e.g. pest or disease resistance and pasture persistence. The testing here was within a selection of ryegrasses, and the greater possible diversity across species may produce different effects. However, these results suggest that highly performing pastures under fertilised and irrigated grazed conditions are best constructed by selecting components that perform well individually than by deliberately introducing diversity between components.