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Context or problem: Selective herbicides control weeds in cereal crops and break down over time, allowing safe planting of legumes in the following years. However due to climatic inconsistencies and changing farming practices, this is not always the case, and residues can inhibit formation of legume/rhizobia symbioses. Objective or research question: The objectives were to determine whether: i) exposure to triasulfuron, even at extremely low levels, reduces shoot and root growth and nodulation of five diverse and widely sown legume pasture cultivars in Australian farming systems; and ii) sowing legumes prior to recommended plant-back criteria being met for chlorsulfuron, triasulfuron herbicide, clopyralid, and pyroxasulfone herbicides results in unacceptable damage to subsequently sown pasture and crop legumes, causing reduced root and shoot growth, nodulation and N fixation. Methods: A series of glasshouse and field experiments explored herbicide residue impact on commonly used legumes in dryland farming systems. Results: A glasshouse study determined triasulfuron at concentration 0.000225 g a.i/ha, a (1/100,000) dilution of the label rate caused significant (p < 0.001) decrease in nodule count, root length, root, shoot weight for Trifolium spumosum cv. Bartolo and T. subterraneum cv. Dalkeith, and at 0.225 g a.i/ha and 2.25 g a.i/ha for all five cultivars tested. A bioassay assessed T. subterraneum cv. Dalkeith health when grown in field soil-cores taken 4, 7 and 10 months after herbicide application (chlorsulfuron, triasulfuron, clopyralid and pyroxasulfone) to a wheat crop. For all three, herbicide residues significantly decreased (p < 0.001) nodule number, shoot weight, root length and whole plant weight of T. subterraneum cv. Dalkeith compared to control. A field experiment assessed nodulation of five pasture and two crop legumes sown dry (dormant summer sowing), or following rainfall 10.5 months after initial herbicide application. Nodulation of all legume cultivars decreased in plots treated with clopyralid. Chlorsulfuron decreased nodulation for all cultivars except T. glanduliferum and T. subterraneum. Triasulfuron reduced nodulation for all cultivars except Ornithopus sativus and T. spumosum. Pyroxasulfone decreased nodulation of Biserrula pelecinus cv. Casbah and Lupinus angustifolius cv. Mandalup. Conclusions: Herbicide residues from preceding cereal crops reduced fitness and symbiotically fixed N in subsequently sown pasture or crop legumes. Implications or significance: Our study highlighted label plant-back recommendations should be strictly adhered to, despite conflict with modern farming approaches of dry or early sowing) to combat climate change. This outcome may consequently lower profitability and increase the carbon footprint of farming systems.

期刊论文 2024-03-15 DOI: 10.1016/j.fcr.2024.109271 ISSN: 0378-4290

Biological nitrogen fixation (BNF) is a high energy-demanding process that may be inhibited by penguin guano. We tested this hypothesis in Ardley Island by measuring BNF in biological soil crusts (BSC) directly within a Penguin Colony and in sites unaffected by penguins. We also explored the effect of adding guano to BSCs in sites free of the influence of penguins. Water availability is also one of the most limiting elements for life in the Antarctica, and we expected that a wetter growing season would stimulate BNF. To evaluate the effect of moisture on BNF, we added water to BSCs under laboratory conditions and estimated BNF by means of the acetylene reduction assay during three growing seasons (2012, 2013 and 2014), with contrasting temperature and precipitation conditions. The results reveal an almost complete inhibition of N fixation in the BSCs of the Penguin Colony. In sites free of ammonium and phosphate in rainwater, BNF rates reached up to 3 kg N ha(-1) year(-1) during warmer and wetter years. The addition of guano to BSCs significantly inhibited the rates of BNF. In laboratory incubations, the addition of water significantly stimulated rates of BNF during the warmer growing season with more sunshine hours. The likely increases in soil moisture levels due to climate change and glacier melting in the Antarctic Peninsula may enhance the rates of BNF. However, this may be constrained by accompanying changes in the distribution of Penguin Colonies.

期刊论文 2017-02-01 DOI: 10.1007/s00300-016-1971-5 ISSN: 0722-4060
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