M. E. Wedderburn

Root growth patterns of perennial ryegrasses under well-watered and drought conditions

Abstract A boroscope and mini-rhizotrons were used to explore root growth patterns in five different ryegrasses grown outdoors under simulated field edaphic conditions including drought. Few major differences in root counts were found among the ryegrasses. The seasonal patterns of root counts in well-watered treatments showed an autumn peak that was later (or even suppressed) as autumn soil temperatures increased in consecutive years. Seasonal patterns were not measurable at more than 7 cm depth down the profile. The summer drought resulted in an increase in root counts right down the profile, which started about a month after the drought began. This was followed by rapid death of roots in the top 15 cm of soil but lower death rates deeper in the soil. After rewetting of the soil, there was a delay of approximately 1 month before a rapid increase in root production occurred. This overcame the apparent high soil temperature inhibition of autumn root growth in the well-watered control treatment.

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.

Heritability of response to moisture stress in a New Zealand North Island hill country ryegrass collection grown with and without nitrogen fertiliser

Abstract The heritability of ryegrass plant response to moisture stress and nonstressed conditions under nil and 3.5 kg nitrogen (N)/week was measured. 39 parent plants (6 clones/parent) and progeny seedlings (6 × 3/parent) were grown in a simulated hill soil profile at 5 cm spacing. One half of the soil bin received 3.5 kg N/week and the other half zero N. A single harvest and tiller count was taken in December. Water was withheld for 85 days, the bin flooded, and dry weight and tiller counts were noted. A second bin was planted with parents and progeny of plants selected for morphological traits. Added N increased tiller number and plant dry weight in the pre-drought measurement with a smaller effect on post-drought measurements. There was a strong phenotypic correlation between tiller number and dry weight post-drought measurement. Seedling-derived offspring were more vigorous than the clonally propagated parental generation. The results indicate significant genetic effects on the ability of ryegrass p...

Genetic differentiation in white clover (Trifolium repens) populations during 8 years of contrasting phosphorus supply in New Zealand hill country

Abstract Genetic differentiation under the selection force of variable soil P availability was measured in populations of two white clover cultivars introduced to a grazed, low fertility grassland site. The resulting mixed grass‐clover pastures subsequently received contrasting levels of phosphorus (P) fertiliser for 8 years. Afield‐based reciprocal transplant experiment and two controlled‐environment experiments were conducted using plants removed from the 8‐year field experiment and appropriate controls to test the hypotheses that: (1) genetic differentiation occurred within the white clover populations in response to variation in P supply; and (2) surviving plants which demonstrated genetic differentiation under high‐P conditions would continue to do this when grown in mixtures with plant material removed from unsown pasture. This study demonstrated that genetic differentiation did occur. In the reciprocal transplant experiment, when returned to a low‐P environment the mean of the populations removed from a low‐P site yielded more than the mean population removed from a high‐P site. Genetic differentiation was demonstrated most strongly with ‘Grasslands Huia’. ‘Huia’ survivors growing in the high‐P source environment retained the potential of the original seed line to respond to P additions, but this potential was lost in ‘Huia’ populations grown under low‐P fertility. In contrast, ‘Grasslands Tahora’ did not retain the potential of the original seed line to respond to additional P and behaved similarly to the resident material. High‐P inputs led to the retention of ‘Huia’ genotypes with the capacity for high growth rates and superior competitive ability. This competitive ability was demonstrated when resident plants grown in a mixture with ‘Huia’ plants removed from the high‐P source treatment suffered reductions in yield compared with their yield in pure pots. The drift by both ‘Tahora’ and ‘Huia’ away from the potential of the original seed attributes towards the resident type demonstrates the adaptive nature of the traits found in the resident population that favour a conservative growth strategy. P availability does not appear to be a dominant selection factor where new germplasm has been introduced to pastures with the objective of stimulating production; maintenance of fertility levels may assist in retaining a full complement of P‐responsive genotypes.

Effect of oversown ryegrass (Lolium perenne) and white clover (Trifolium repens) on the genetic structure of New Zealand hill pastures

Abstract The botanical composition and genetic structure of North Island hill pastures were studied after oversowing. Three pre‐sowing treatments were applied: (a) no herbicide; (b) herbicide to suppress existing pasture; and (c) herbicide to kill existing pasture. Four oversowing treatments were imposed: (1) no oversowing; (2) hill country ryegrass and ‘Prop’ white clover; (3) ‘Yatsyn’ ryegrass and ‘Prop’ white clover; and (4) a mixture of hill country grass species. Five times as many ryegrass seeds were oversown than emerged from buried seed, giving the introduced material an advantage. The ryegrass content was greater at the high‐fertility sites than at the low‐fertility sites, both before and after oversowing. Killing the original pasture tended to increase ryegrass content for 16 months at the low‐fertility sites but increased the ryegrass content for less than 9 months at the high‐fertility sites. The ryegrass content was not significantly different on any of the sown and unsown plots, 16 months af...

Improving the economic and environmental performance of a New Zealand hill country farm catchment: 2. Forecasting and planning land‐use change

Abstract The second phase of a multi‐stakeholder, integrated catchment management project at the Whatawhata Research Centre is described. This project explored land use and management change options to improve the economic and environmental performance of the case study hill land catchment farm. Research observations, decision support models and expert stakeholder knowledge were used to develop and predict the outcome of various scenarios for the key performance indicators identified by the Catchment Management Group (CMG). These scenarios included Pinus radiata plantation forestry, livestock intensification and enterprise change, riparian revegetation, indigenous forest restoration and pastoral land stabilisation with erosion control plantings. The resulting predictions did offer scope for improving both the economic and environmental performance of the case study catchment farm, if the time scale for change was not a constraint. The CMG developed a new land‐use plan in order to meet the diverse economic and environmental goals they had originally identified for a “well managed hill land catchment”. The feasibility of this plan depended on significant capital investment in land use and enterprise change, and the outcomes were likely to take up to 30 years to manifest themselves in the key performance indicators.

Comparison of improved “low-fertility” grass species and ryegrass with wild populations for performance under varying levels of nitrogen and moisture in a simulated hill soil profile

Abstract This study compared improved “low-fertility” grass species and ryegrass with wild populations for performance under varying levels of nitrogen (N) and moisture. The species studied were: Lolium perenne L.; Agrostis capillaris L.; Cynosurus cristatus L.; Festuca rubra L.; Dactylis glomerata L.; Anthoxanthum odoratum L.; Bromus mollis L.; and Holcus lanatus L. Wild-type seed was collected randomly from moderate hill country; bred genotypes were either selection lines, cultivars, or random collections. The plants were grown in simulated hill soil profiles. Each species was represented by 24 seedlings planted in a 6 × 4 block. N was applied in solution at three concentrations (0, 7, and 21 kg N/ha per fortnight). Three harvests were taken. A rain shelter was placed over the plants from December until February 1991 and recovery yield noted. Throughout the N experiment, yields of wild and bred genotypes of the same species were generally similar. The response to N differed. During Harvest 2, ryegrass s...

Allozyme variation within and between three populations of browntop (Agrostis capillaris)

Abstract Allozyme variation in the tetraploid browntop (Agrostis capillaris) cultivar ‘Grasslands Muster’, and two resident hill country browntop populations was investigated. The aim was to develop a set of genetic markers that would allow this cultivar to be reliably distinguished from the resident populations, enabling persistence of this cultivar in hill country pastures to be monitored following oversowing. Screening of 17 enzyme systems yielded three polymorphic loci: Gpi; Pgm; and Mdh. For Gpi, 12 alleles were found among the three populations sampled, allele frequencies ranging from 0 to 0.245. Pgm showed six alleles, and frequencies ranged from 0 to 0.792. Mdh could only be analysed in terms of phenotype frequencies, and four phenotypes were recognised, with frequencies ranging from 0 to 0.6. Pairwise G‐tests and the calculation of geometric distances between the populations on the basis of this data suggested that allele frequencies at the loci Gpi and Pgm differ sufficiently between ‘Grasslands...

Allozyme markers suitable for pasture persistence studies in cocksfoot (Dactylis glomerata) cv. Grasslands Wana

Abstract Allozyme variation in the tetraploid cocksfoot (Dactylis glomerata) cv. Grasslands Wana was studied with a view to establishing a set of genetic markers that would enable this cultivar to be distinguished from resident cocksfoot populations. Such markers would enable the persistence of ‘Grasslands Wana’ in hill country pastures to be monitored following oversowing, via the estimation of the admixture proportion of the cultivar in the resulting pasture mixture. Three of the six enzyme systems studied proved to be polymorphic, yielding four marker loci: Mdh‐1; Pgm; and the isolocus Gpi‐1,2. Five alleles were found for Gpi‐1,2, with frequencies ranging from 0.04 to 0.55. For Pgm three alleles of intermediate frequency were found, and Mdh‐1 showed two alleles with frequencies of 0.91 and 0.09. These loci will provide a useful tool for following the persistence of ‘Grasslands Wana’ in a mixed pasture, provided the genotype and allele frequencies of the resident pasture populations differ suffficiently...