M Boersma

Influence of selected environmental factors on glyphosate efficacy when applied to awnless barnyard grass ( Echinochloa colona (L.) Link)

Glasshouse experiments were conducted to determine the effects of various environmental factors on glyphosate efficacy when applied to Echinochloa colona (L.) Link (awnless barnyard grass) plants. The variables examined were 4 soil moisture conditions (29, 42, 55, and 100% of field capacity), 2 levels of irradiance (400 and 800 µmol/m2· s), 3 temperature regimes (20/15, 30/25, and 35/30°C; day/night), and 2 levels of relative humidity (92 and 65%). The efficacy of 360 g acid equivalent glyphosate/ha was greatest when applied to well-watered (field capacity) plants that were placed under cool (20/25°C) and humid (92% relative humidity) conditions. The efficacy was least when applied to plants under severe water stress (29% of field capacity) that were placed under hot (35/30°C) and less humid (65% relative humidity) conditions. In all experiments, efficacy was not altered by the level of irradiance.

In Situ Persistence and Migration of Biochar Carbon and Its Impact on Native Carbon Emission in Contrasting Soils under Managed Temperate Pastures

Pyrogenic carbon (PyC) is an important component of the global soil carbon (C) pool, but its fate, persistence, and loss dynamics in contrasting soils and environments under planted field conditions are poorly understood. To fill this knowledge gap, a 13C-labelled biochar, as a surrogate material for PyC, produced from Eucalyptus saligna by slow pyrolysis (450°C; δ13C -36.7‰) was surface (0−10 cm) applied in C3 dominated temperate pasture systems across Arenosol, Cambisol and Ferralsol. The results show a low proportion of the applied biochar-C mineralised over 12 months in a relatively clay- and C-poor Arenosol (i.e., 2.0% loss via mineralisation), followed by a clay- and C-rich Cambisol (4.6%), and clay-, C- and earthworm-rich Ferralsol (7.0%). The biochar-C mean residence time (MRT), estimated by different models, varied between 44−1079 (Arenosol), 18−172 (Cambisol), and 11−29 (Ferralsol) years, with the shorter MRT estimated by a one-pool exponential and the longer MRT by an infinite-pool power or a two-pool exponential model. The two-pool model was best fitted to biochar-C mineralisation. The biochar-C recovery in the 12−30 cm soil layer varied from between 1.2% (Arenosol), 2.5−2.7% (Cambisol) and 13.8−15.7% (Ferralsol) of the applied biochar-C after 8−12 months. There was a further migration of biochar-C below the 50-cm depth in the Arenosol, as the combined biochar-C recovery in the mineralised pool and soil profile (up to 30 or 50 cm) was 82%, in contrast to 101% in the Cambisol and 104% in the Ferralsol after 12 months. These results indicate that the downward migration of biochar-C was greatest in the Arenosol (cf. Cambisol and Ferralsol). Cumulative CO2-C emission from native soil-plant sources was lower (p <0.10) in the biochar-amended vs. non-amended Ferralsol. This field-based study shows that the downward migration of biochar-C exceeded its loss via mineralisation in the Arenosol and Ferralsol, but not in the Cambisol. It is thus important to understand biochar-soil interactions to maximise long-term biochar C sequestration potential in planted soil systems.

Opportunities and constraints for biochar technology in Australian agriculture: looking beyond carbon sequestration

The application of biochar technology for soil amendment is largely based on evidence about soil fertility and crop productivity gains made in the Amazonian Black Earth (terra preta). However, the uncertainty of production gains at realistic application rates of biochars and lack of knowledge about other benefits and other concerns may have resulted in poor uptake of biochar technology in Australia so far. In this review, we identify important opportunities as well as challenges in the adoption of biochar technology for broadacre farming and other sectors in Australia. The paper highlights that for biochar technology to be cost-effective and successful, we need to look beyond carbon sequestration and explore other opportunities to value-add to biochar. Therefore, some emerging and novel applications of biochar are identified. We also suggest some priority research areas that need immediate attention in order to realise the full potential of biochar technology in agriculture and other sectors in Australia.

Relationship between vigour tests and emergence of soybean when grown under a range of seedbed moisture conditions

Laboratory vigour tests were performed on seed from 4 soybean [Glycine max (L.) Merr.] cultivars coming from commercial crops grown in eastern Australia. The seed from each cultivar had greater than 80% germination and a range in vigour. Vigour tests consisted of the accelerated aging (with or without a seed protectant, Thiram), cold, saturation and hypocotyl length tests. Results were compared with seedling emergence from the same cultivar when planted under growth room conditions (25/20 ± 1°C, 14/10 h day/night) at 3 seedbed moisture levels (field capacity, -0.01 MPa; dry, -0.30 MPa; and saturated soil, soil saturated for 48 h, planted then allowed to dry to field capacity). The modified accelerated aging test with Thiram was significantly (P<0.01) correlated with emergence in all 3 seedbed moisture conditions. High vigour seed samples with high accelerated aging germinations emerged well. Overall, the vigour test which ranked the seed samples to give the best indicator of performance under a range of seedbed moisture conditions was the modified accelerated aging test with thiram.

Relationship between growth rate and the development of hollow stem in broccoli

Boron deficiency is widely accepted as the dominant cause of hollow stem in broccoli (Brassica oleracea L. var. italica Plenck), although high growth rate has also been mentioned in the literature as a possible cause of the disorder. In this study, we investigated the role of growth rate and boron in the development of hollow stem. Two experiments were conducted with broccoli cv. Marathon, using planting density to manipulate growth rate. In the first experiment, plants were grown at 3 planting densities (19 512, 32 520, and 69 686 plants/ha) and either supplemented or not supplemented with foliar boron applications (0.35 kg B/ha) on two occasions. In the second experiment, broccoli plants at 2 planting densities (32 520 and 100 000 plants/ha) were treated in factorial combination from inflorescence initiation onwards with complete trace element fertiliser (1.5% B), 57% light interception, and paclobutrazol (480 g a.i./ha). The incidence and severity of hollow stem were assessed using digital image analysis and were found to increase with plant spacing but were not affected by boron application. The probability of hollow stem occurring increased with absolute growth rate in the first trial, but not the second. Absolute growth rate, measured as dry weight accumulation, was suppressed independently of planting density by the shading treatment, but did not influence the incidence or severity of hollow stem. The application of paclobutrazol did not influence absolute growth rate but reduced the severity of hollow stem at the lowest planting density. Our data support the hypothesis that the rate and pattern of growth are involved in the development of hollow stem, and that a boron deficiency is not the major causal factor.

Impact of biochar application on the productivity of a temperate vegetable cropping system

ABSTRACT Few studies have investigated the potential of biochar in supporting cool temperate horticultural systems with fertile soils. We examined the effects of applying 10 t ha−1 of blue mallee (Eucalyptus polybractea) biochar in combination with fertiliser rate treatments (either full or half the regional recommended rate) on crop yield, yield parameters and soil properties of a cool temperate vegetable cropping system on a red Ferrosol. Biochar amendment did not improve crop yield or other yield parameters of cauliflower, peas and broccoli crops. Similarly, soil parameters including nitrate and ammonium were unaffected by biochar treatment. We suggest the lack of biochar effect on crop and soil parameters was related to the inherent chemical fertility and structural robustness of Ferrosols, which may have mitigated any potential benefits from biochar amendment. Our results demonstrate that biochar application may not bring significant soil quality and crop productivity improvements to high-input agricultural systems.