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Brave the wild river : the untold story of two women who mapped the botany of the Grand Canyon
In the summer of 1938, botanists Elzada Clover and Lois Jotter set off down the Colorado River, accompanied by an ambitious expedition leader and three amateur boatmen. With its churning rapids, sheer cliffs and boat-shattering boulders, the Colorado River was famed as the most dangerous river in the world. But for Clover and Jotter, it held a tantalising appeal: no one had surveyed the Grand Canyon's plants, and they were determined to be the first. Through the vibrant letters and diaries of the two women, science journalist Melissa L. Sevigny traces their forty-three-day journey, during which they ran rapids, chased a runaway boat and turned their harshest critic into an ally. Their story is a spell-binding adventure of two women who risked their lives to make an unprecedented botanical survey of a little-known corner of the American West at a time when human influences had begun to change it forever.
Book
Increasing Crop Diversity Mitigates Weather Variations and Improves Yield Stability
Cropping sequence diversification provides a systems approach to reduce yield variations and improve resilience to multiple environmental stresses. Yield advantages of more diverse crop rotations and their synergistic effects with reduced tillage are well documented, but few studies have quantified the impact of these management practices on yields and their stability when soil moisture is limiting or in excess. Using yield and weather data obtained from a 31-year long term rotation and tillage trial in Ontario, we tested whether crop rotation diversity is associated with greater yield stability when abnormal weather conditions occur. We used parametric and non-parametric approaches to quantify the impact of rotation diversity (monocrop, 2-crops, 3-crops without or with one or two legume cover crops) and tillage (conventional or reduced tillage) on yield probabilities and the benefits of crop diversity under different soil moisture and temperature scenarios. Although the magnitude of rotation benefits varied with crops, weather patterns and tillage, yield stability significantly increased when corn and soybean were integrated into more diverse rotations. Introducing small grains into short corn-soybean rotation was enough to provide substantial benefits on long-term soybean yields and their stability while the effects on corn were mostly associated with the temporal niche provided by small grains for underseeded red clover or alfalfa. Crop diversification strategies increased the probability of harnessing favorable growing conditions while decreasing the risk of crop failure. In hot and dry years, diversification of corn-soybean rotations and reduced tillage increased yield by 7% and 22% for corn and soybean respectively. Given the additional advantages associated with cropping system diversification, such a strategy provides a more comprehensive approach to lowering yield variability and improving the resilience of cropping systems to multiple environmental stresses. This could help to sustain future yield levels in challenging production environments.
Journal Article
Marginal increase in nitrate leaching under grass–clover leys by slurry and mineral fertilizer
On dairy farms, fertilization of grass-clover swards ensures stable grass yields but may increase the potential for nitrate leaching on light-textured soils. The aim of this study was to quantify the N use efficiency and nitrate leaching under fertilized grass-clover leys. The study was conducted over 2 years at two sites, with increasing applications of mineral fertilizer (0–480 kg available N ha
−1
) alone or in combination with a basic application of cattle slurry. For plots fertilized with mineral N, the N soil surface balance was independent of the application rate and in the same range as for unfertilized plots (− 11 to 51 kg N ha
−1
). However, when plots were fertilized with slurry N (+ mineral N), the surplus was substantially increased owing to the fraction of organic N applied in slurry (95–100 kg N ha
−1
) and higher biological N
2
fixation inputs (55–228 kg N ha
−1
). The type of fertilizer had no effect on nitrate leaching across the full range of application rates. Nitrate leaching increased quadratically as a function of application rate, with a range of 3–117 kg N ha
−1
(0.33–17 mg l
−1
in soil solution sampled with suction cups) in the first year and less in the second year, when clover proportion was lower due to the self-regulatory nature of grass-clover mixtures. Importantly, the rate of marginal leaching increased with fertilization level: below 150 kg N ha
−1
there was no additional leaching from fertilization and at 200 kg N ha
−1
around 5% of additional fertilizer-N was leached. This is less than generally found for arable crops and thus even in intensive dairy systems, grass-clover leys are an environmentally favorable crop.
Journal Article
High spatial variation in population size and symbiotic performance of Rhizobium leguminosarum bv. trifolii with white clover in New Zealand pasture soils
Examines the extent in variation in the properties of a) variation in the population size and b) the effectiveness of N-fixation at three differentspatial scales namely: from 26 sites across New Zealand; at farm-wide scale; and within single fields. Source: National Library of New Zealand Te Puna Matauranga o Aotearoa, licensed by the Department of Internal Affairs for re-use under the Creative Commons Attribution 3.0 New Zealand Licence.
Journal Article
Local adaptation, genetic diversity and key environmental interactions in a collection of novel red clover germplasm
Red clover (Trifolium pratense L.) is known for its large taproot, nitrogen fixation capabilities and production of forage high in protein and digestibility. It has the potential to strengthen temperate pastural systems against future adverse climatic events by providing higher biomass during periods of water deficit. Being outcrossing and self-incompatible, red clover is a highly heterozygous species. If evaluated and utilized correctly, this genetic diversity can be harnessed to develop productive, persistent cultivars. In this study, we selected 92 geographically diverse red clover novel germplasm populations for assessment in multi-location, multi-year field trials and for genetic diversity and genetic relationship characterization using pooled genotyping-by-sequencing (GBS). Through the development of integrated linear mixed models based on genomic, phenotypic, and environmental information we assessed variance components and genotype-by-environment (G x E) interactions for eight physiological and morphological traits. Key interactions between environmental variables and plant performance were also evaluated using a common garden site at Lincoln. We found that the genetic structure of the 92 populations was highly influenced by country of origin. The expected heterozygosity within populations ranged between 0.08 and 0.17 and varied with geographical origin. For the eight physiological and morphological traits measured there was high narrow-sense heritability (h2 > 0.70). The influence of environmental variables, such as mean precipitation, temperature and isothermality of the original collection locations, on plant and trait performance in the local field trials was also highlighted. Along with the identification of genes associated with these bioclimatic variables that could be used as genetic markers for selection in future breeding programs. Our study identifies the importance of diverse germplasm when adding genetic variation into breeding programs. It also identifies efficient evaluation methods and key climatic variables that should be considered when developing adaptive red clover cultivars.
Journal Article
Increasing Cropping System Diversity Balances Productivity, Profitability and Environmental Health
Balancing productivity, profitability, and environmental health is a key challenge for agricultural sustainability. Most crop production systems in the United States are characterized by low species and management diversity, high use of fossil energy and agrichemicals, and large negative impacts on the environment. We hypothesized that cropping system diversification would promote ecosystem services that would supplement, and eventually displace, synthetic external inputs used to maintain crop productivity. To test this, we conducted a field study from 2003–2011 in Iowa that included three contrasting systems varying in length of crop sequence and inputs. We compared a conventionally managed 2-yr rotation (maize-soybean) that received fertilizers and herbicides at rates comparable to those used on nearby farms with two more diverse cropping systems: a 3-yr rotation (maize-soybean-small grain + red clover) and a 4-yr rotation (maize-soybean-small grain + alfalfa-alfalfa) managed with lower synthetic N fertilizer and herbicide inputs and periodic applications of cattle manure. Grain yields, mass of harvested products, and profit in the more diverse systems were similar to, or greater than, those in the conventional system, despite reductions of agrichemical inputs. Weeds were suppressed effectively in all systems, but freshwater toxicity of the more diverse systems was two orders of magnitude lower than in the conventional system. Results of our study indicate that more diverse cropping systems can use small amounts of synthetic agrichemical inputs as powerful tools with which to tune, rather than drive, agroecosystem performance, while meeting or exceeding the performance of less diverse systems.
Journal Article
Climate impact of alternative organic fertilizers using life cycle assessment
Anaerobic digestion is a common method for managing liquid manure and other biomasses, generating biogas as a renewable energy source. The resulting digestate can be processed into organic fertilizers to enhance nutrient recycling, but its environmental impact warrants investigation. In this study, a life cycle assessment was conducted to examine the impact of fertilizers derived from cattle slurry and grass–clover co-digestion on global warming (measured in CO2 equivalents) compared to untreated cattle slurry (CA). The different treatments analyzed include CA, digestate, liquid fractions (LFs) from digestate separation, and an enriched liquid nitrogen–sulfur product derived from post-processing of biogas and drying of the solid fraction. The functional units of this study were 100 kg of total nitrogen in the final organic fertilizer (FU1) with the cradle-to-processing gate boundary, and the harvesting of 1 ton of spring barley dry matter (FU2) with the cradle-to-field application boundary. The carbon footprint ranged from 24% to 49% of the baseline scenario for FU1, and from −6% to 177% of the baseline scenario for FU2. The main contributors to the carbon footprint of fertilizers included greenhouse gas emissions from storage and field application. However, biogas production from anaerobic digestion, together with the concurrent mitigation of CH4 emissions during storage, contributed most to a reduction in the overall global warming potential associated with anaerobic digestate and its LF. This study showed large climate prospects in replacing untreated slurry as organic fertilizer with alternatives resulting from its anaerobic digestion and post-treatment.
Journal Article
Growth and root dry matter allocation by pasture legumes and a grass with contrasting external critical phosphorus requirements
Background and aims This work aimed to quantify the critical external requirement for phosphorus (P) (i.e. extractable-P concentration required for 90% of maximum yield) for a number of temperate legume species and understand differences in dry matter allocation, P distribution and P acquisition efficiency among these species. Methods Shoot and root growth of five legume and one grass species was assessed in response to six rates of P mixed into the top 45 mm of soil in a pot experiment. Dactylis glomerata and Trifolium subterraneum were used as benchmark species; they are commonly grown together in mixed temperate pastures and have low and high critical external requirements for P, respectively. Growth was compared with four alternative legume species: Ornithopus compressus, Ornithopus sativus, Biserrula pelecinus and Trifolium hirtum, that have root morphologies better suited to soil exploration and nutrient acquisition than that of Trifolium subterraneum. Results Dactylis glomerata, Ornithopus compressus and Ornithopus sativus had maximum yields equal to or greater than Trifolium subterraneum but achieved this at rates of P less than half that of Trifolium subterraneum. Biserrula pelecinus and Trifolium hirtum had critical P requirements between that of Trifolium subterraneum and the Ornithopus species, but also had lower yields. Root dry matter of Dactylis glomerata and the Ornithopus species in the fertilised soil layer was only marginally changed in response to low P supply. In contrast, Trifolium subterraneum, Trifolium hirtum and to a lesser extent Biserrula pelecinus markedly increased root dry matter allocation to this soil layer. Species with lower critical P requirements were able to take up more P per unit root dry mass than those with higher critical P requirements, particularly at lower levels of P addition. Conclusions The high P acquisition efficiencies of the Ornithopus species and Dactylis glomerata were likely to have contributed to their low critical external P requirements. It was surmised that differences in root morphology traits underpin the differences in acclimation to low P stress and P acquisition efficiency among the species.
Journal Article
Biological N₂-fixation in grass-clover ley in response to N application in cattle slurry vs. mineral fertilizer
Background
The nitrogen (N) response in grass-clover is influenced by quantity and timing of N-fertilizer, but less is known about the effect of fertilizer type (animal manure vs. mineral N) and N form (ammonium vs. nitrate).
Method
A field trial was established in a mixture of white clover (
Trifolium repens
L.), red clover (
Trifolium pratense
L.) and perennial ryegrass (
Lolium. perenne
L.) with mineral N and slurry. DM yield in grass and clover and N
2
-fixation activity (%Ndfa) was determined in four cuts during the season.
Results
Fertilization resulted in a peak in soil mineral N within 1-2 weeks of application and decreased to background rate prior to plant harvest. No differences in white clover N
2
-fixation activity were found between fertilizer types within each N level.
Conclusions
The experiment showed that mineral N form does not affect the regulation of N
2
-fixation activity. The fertilizer N level was the only factor affecting white clover N
2
-fixation activity. Further, the results demonstrated an N threshold below which annual %Ndfa was always high (~90%). This was controlled by the companion grass’ ability to deplete the soil mineral N pool. When N fertilization exceeded this threshold (above 180 kg N ha
-1
yr
-1
in our case) annual %Ndfa significantly decreased as did qBNF in the harvested biomass.
Journal Article