The global phosphate rock reserves that underpin phosphorus (P) fertiliser production are finite. Recovery of P from waste streams (e.g., by producing fertiliser products from sewage sludge) is an ...important way to conserve scarce P resources. This study evaluated the P fertiliser and soil pH amendment values of a municipal sewage sludge ash (SA) for pasture growth on three acidic soils with contrasting P buffering and P sorption (“fixation”) characteristics. Growth of subterranean clover (
Trifolium subterraneum
L.) and incubation of the fertilisers with soil were used to compare the initial (following application) and residual (following incubation with soil) fertiliser values of SA with those of single superphosphate (SSP). Soil pH
Ca
was increased linearly by application of SA. The lime-equivalent value of SA was ~ 33% (product weight basis). The initial P-fertiliser value of SSP was substantially greater than that of SA in all three soils. For both P sources, initial fertiliser value was negatively related with the P buffering capacity of the soil. The residual P fertiliser value of SSP ranged from low (42% of initial fertiliser value) to relatively high (82%) indicating differences among the soils in their P sorption capacities. The residual value of SA was better than that of SSP in soils that exhibited strong P-sorption capacities. Standard soil-P tests (i.e., Colwell P, CaCl
2
-P, Bray-1 P) that are often used in combination with SSP, underpredicted the fertiliser value of SA. This indicated a need to recalibrate these soil tests for use with SA.
Subterranean clover (
) is a critical pasture legume in Mediterranean regions of southern Australia and elsewhere, including Mediterranean-type climatic regions in Africa, Asia, Australia, Europe, ...North America, and South America. Pythium damping-off and root disease caused by
is a significant threat to subterranean clover in Australia and a study was conducted to define how environmental factors (viz. temperature, soil type, moisture and nutrition) as well as variety, influence the extent of damping-off and root disease as well as subterranean clover productivity under challenge by this pathogen. Relationships were statistically modeled using linear and generalized linear models and boosted regression trees. Modeling found complex relationships between explanatory variables and the extent of Pythium damping-off and root rot. Linear modeling identified high-level (4 or 5-way) significant interactions for each dependent variable (dry shoot and root weight, emergence, tap and lateral root disease index). Furthermore, all explanatory variables (temperature, soil, moisture, nutrition, variety) were found significant as part of some interaction within these models. A significant five-way interaction between all explanatory variables was found for both dry shoot and root dry weights, and a four way interaction between temperature, soil, moisture, and nutrition was found for both tap and lateral root disease index. A second approach to modeling using boosted regression trees provided support for and helped clarify the complex nature of the relationships found in linear models. All explanatory variables showed at least 5% relative influence on each of the five dependent variables. All models indicated differences due to soil type, with the sand-based soil having either higher weights, greater emergence, or lower disease indices; while lowest weights and less emergence, as well as higher disease indices, were found for loam soil and low temperature. There was more severe tap and lateral root rot disease in higher moisture situations.
The soils of Mediterranean semiarid environments are commonly characterized by low levels of organic matter and mineral elements, as well as severe weed infestations, which, taken together, cause an ...intensive use of auxiliary inputs (tillage, fertilizers, herbicides). Although cover crops are recognized to sustainably improve soil health, the impact of
Trifolium subterraneum
L. cover cropping needs specific attention. This research investigates for the first time the effects over 4 years of
T. subterraneum
and spontaneous flora cover crops, after either incorporating their dead mulches into the soil or leaving them on the soil surface, on soil organic matter (SOM), macroelements, mineral nitrogen, microelements, and weed seedbank dynamics as indicators of soil quality in an apricot orchard. Compared to a conventional management control, the
T. subterraneum
cover crop with the burying of dead mulch into the soil increased the amount of SOM (+ 15%), ammoniacal (+ 194%) and nitric (+ 308%) nitrogen, assimilable P
2
O
5
(+ 5%), exchangeable K
2
O (+ 14%), exchangeable Na (+ 32%), exchangeable K (+ 16%), Fe (+ 15%), Mn (+ 28%), Zn (+ 36%), and Cu (+ 24%), while it decreased the weed seedbank size (‒ 54%) and enhanced weed biodiversity. These findings suggest that
T. subterraneum
cover cropping may be an environment-friendly tool to enhance soil quality and limit auxiliary input supply in Mediterranean orchards.
Prospects for improving the productivity of species mixtures in transitions between phases by changing row configuration at sowing were examined in two series of field experiments in rain‐fed, ...semi‐arid environments in south‐eastern Australia. The first series explored how the choice of cover crop and use of alternate drill row configurations affected establishment and yields of sward components in the transition from a cropping into a pasture phase. Cover‐crop species included wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola (Brassica napus L.) and lupins (Lupinus augustifolius L.), each sown in mixed or alternate drill rows with lucerne (Medicago sativa L.) and subterranean clover (Trifolium subterraneum L.). The second series of experiments examined the productivity implications when returning from the pasture phase back into cropping following 10 contrasting pastures sown to various combinations of lucerne, subterranean clover or phalaris (Phalaris aquatica L.) sown in mixed, alternate (1:1) or double skip (1:2) row configurations in the absence of cover crops. All experiments were sown on a 0.25‐m row spacing. In the transition into the pasture phase, grain yields of cover crops in the mixed drill row treatment were similar to those achieved by crops grown in the absence of pasture species but were reduced by an average of 24% in the alternate drill row configuration. Canola and lupin crop biomass were lower, compared with wheat and barley, leading to increased pasture yields in year 1, highlighting an opportunity for increased use of these species as cover/companion crops in semi‐arid environments. Pasture yields beyond year 1 were reduced by ~20% in the alternate drill row treatments compared with where species were sown in mixed drill rows, with greater yield differences under more favourable growing conditions. This response largely reflected yield reductions in lucerne where it was concentrated in fewer drill rows. The alternate drill row configuration increased the abundance of subterranean clover in year 1, but this species remained a minor component of all swards beyond the establishment year. In the transition into the cropping phase, effects on grain quality could only be attributed to row configuration of the previous pasture to the extent that row configuration changed pasture composition. Grain size was smallest and protein concentration highest where previous pastures contained both lucerne and subterranean clover without phalaris. Taken together, there was little advantage in total productivity attributable to spatially separating species in drill rows at sowing.
The annual regeneration from seeds of subterranean clover plants after initial sowing depends on the hardseededness (HS
max
, %), its breakdown rate (HS
break
, %/ °C) and the germinability of the ...seeds over time. Hardseededness is a physical mechanism of dormancy that prevents germination of seeds and is ecologically important for the persistence of subterranean clover in a range of environments. The effects of genotype (G) and sowing time (environment, E) on hardseedednes and germination were investigated for 'Antas', 'Denmark', 'Leura', 'Monti', 'Narrikup' and 'Woogenellup' harvested from six different sowing dates (June 2015-March 2016) in a field experiment in Canterbury, New Zealand. 'Antas' had a lower HS
max
(53%) than 'Monti' (86%). HS
break
was affected by the G x E interaction with a doubling of HS
break
from 0.011%/°C for the June sowing date to ∼0.02%/°Cd for the February sowing date for 'Denmark', 'Leura', 'Monti' and 'Narrikup'. There was less sensitivity of 'Antas' and 'Wogenellup' to sowing time. There was an increase in the percentage of abnormal seedlings as the sowing date advanced from winter to late-summer. The developed parameters enabled estimation of seedling emergence and indicate cultivars which have a competitive advantage of an early seedling regeneration in temperate regions.
Aims
Phosphorus (P) is usually stratified in the topsoil layer under pasture, due to the broadcast application of fertiliser, excreta and leaf-litter deposition on the soil surface, and minimal soil ...disturbance. The objective of this study was to investigate root proliferation and P acquisition in response to P stratification by comparing two
Trifolium subterraneum
cultivars with contrasting root morphologies.
Methods
Clover micro-swards were grown with deficient, constrained and sufficient P supplied in a topsoil layer overlying a P-deficient subsoil that mimicked the stratification of P that occurs under pasture. Phosphorus labelled with
33
P- and
32
P-radioisotope tracer was mixed throughout the topsoil and subsoil layers, respectively.
Results
The shoot yield and total plant P uptake of the cultivars increased in response to increased topsoil P supply. The length of roots produced by the cultivars was equivalent in each of the P treatments, although the specific root length achieved by the cultivars was substantially different. In the P-constrained and P-sufficient treatments, ~91% and ~ 99% of total plant P was acquired by topsoil roots, respectively. In contrast, subsoil roots acquired 60–74% of total plant P in the P-deficient treatment.
Conclusions
Topsoil roots were most important for P acquisition when P was highly stratified, whereas subsoil roots contributed to P acquisition when P was uniformly distributed throughout the P-deficient soil profile. Selection for prolific nutrient-foraging roots, in conjunction with plasticity for subsoil exploration, may improve the P-acquisition efficiency of
T. subterraneum
genotypes and confer adaptability across a range of soil-P environments.
One of the most widespread methodologies used to describe phenological stages in plants was developed by the Biologische Bundesanstalt Bundessortenamt und Chemische Industrie (BBCH). The BBCH scale ...utilises a decimal‐code system that divides plant phenological stages into a binary code composed of the principal and the secondary stages. This system has been extensively used to describe the phenological stages of diverse species, but there is no phenological description that can aid researchers in defining the duration of phenological stages of annual Mediterranean forage legumes that present different growth habits. The development of a precise phenological scale for forages enables the determination of grazing management strategies to attain a desired forage yield and quality as to precisely define the timing of agronomical practices. We have adapted the BBCH decimal‐code scale for Medicago polymorpha, Trifolium alexandrinum, Trifolium subterraneum, and Vicia benghalensis. The scale consists of 10 main stages with specific secondary stages. Descriptive keys with illustrations will help identify any particular phenological stage for each species. The scales presented here will aid researchers and the agricultural community in clearly defining the timing of agronomical practices, such as the appropriate time for grazing/harvest of these species.
Phenological Stage 0 of (a) Medicago polymorpha, (b) Trifolium alexandrinum, (c) Trifolium subterraneum, and (d) Vicia benghalensis, based on the BBCH decimal‐code scale.
AIMS: The legumes most often used in temperate pastures such as Trifolium subterraneum have relatively high external P requirements for maximum growth. We investigated root traits associated with P ...acquisition in current and novel pasture legumes, as well as temperate grasses which have lower P requirements. METHODS: Thirteen legume species, two pasture grasses, and three high carboxylate-exuding crop species (Lupinus albus, L. angustifolius, Cicer arietinum) were grown in a glasshouse for six weeks. Rhizosphere carboxylates and root morphological traits were measured. RESULTS: Ornithopus spp. had rhizosphere carboxylates in similar quantities to the Lupinus spp. (> 40 μmol g⁻¹ root dry mass). Trifolium subterraneum lines had relatively large average root diameter, reduced specific root length and very short average root hair length resulting in specific root hair cylinder volumes (RHCVs) only 14–20 % of the grasses. However, O. sativus, O. compressus and Biserrula pelecinus had specific RHCVs more comparable to the grasses. CONCLUSIONS: Novel pasture legume species with root morphology more comparable to that of grasses than T. subterraneum were identified. Of these, Ornithopus spp. were notable as they also had high rhizosphere carboxylates relative to root dry mass.
Forage systems can be designed to produce high quality feed for ruminant livestock while providing habitat for insect pollinators. We compared forage productivity, nutritive value, and selenium ...uptake as well as late summer nectar production of perennial forage species; alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), red clover (Trifolium pratense), sainfoin (Onobrychis viciifolia), and chicory (Cichorium intybus) as monocultures and intercropped with either subterranean clover (Trifolium subterraneum) or balansa clover (Trifolium michelianum) for two successive years in Oregon. Red clover intercropped with balansa clover out‐performed other stands, producing over 11 t DM ha−1 in 2019 and 9.4 t DM ha−1 in 2020. Birdsfoot trefoil and sainfoin mixtures were dominated by subterranean clover, negatively affecting total forage yield and flower abundance. Chicory intercropped with subterranean clover formed a more balanced mixture with improved DM yield and nutritive value relative to chicory monocultures. Chicory was most responsive to Se‐fertilisation in both years, having a higher concentration of Se relative to the other perennial species. Chicory also had high levels of condensed tannins (18.1–43.3 mg/g DM) relative to the other forages (1.8–17.5 mg/g DM). Red clover had the most consistent bloom in 2019, with 170 inflorescences per square meter at peak bloom and yielded an estimated total of 16.9 kg ha−1 sucrose. Birdsfoot trefoil produced the most inflorescences during peak bloom in 2020 at 279 inflorescences per square meter. However, alfalfa had a higher estimated sucrose yield in 2020 at 241 kg ha−1.
Subterranean clover (Trifolium subterraneum) is an important pasture legume, and Sardinia is known as a major centre of diversification of this species. As other legumes, this clover produces ...biologically active flavonoids including the subclass of isoflavones that are natural phytoestrogens with positive health effects. Present sources of isoflavones for medical/nutraceutical treatments are red clover (Trifolium pratense) and soybean (Glycine max). This study assessed the content and composition of flavonoids in 14 subterranean clover genotypes from Sardinia, grown ex‐situ in comparison with two red clover ecotypes, to acquire information on the potential of the species as an alternative source of isoflavones for possible exploitation. Twenty compounds were tentatively identified across the two clovers after HPLC and LC/ESI‐MS analyses, including clovamide, four flavonols, and 15 isoflavones. Most compounds were present as glucosides or glucosyl malonates. Subterranean clover extracts mainly comprised of derivatives of the isoflavones genistein, biochanin A, and formononetin. Compared to red clover, subterranean clover had higher content of total isoflavones and lower concentration of total flavonols. The isoflavone concentration in subterranean clover was higher than literature data for soybean or red clover. The existing genotypic variation warrants the possibility of selecting varieties with high isoflavone concentration for nutraceutical or pharmaceutical purposes.
Isoflavone Content in Subterranean Clover Germplasm from Sardinia
A. Tava*, A. Stochmal, L. Pecetti
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