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Purpose Chicory ( Cichorium intybus ) scavenges more soil mineral nitrogen (N) than perennial ryegrass ( Lolium perenne ). A glasshouse study was conducted to test whether (a) the percentage of N derived from the atmosphere (%Ndfa) by a companion legume differs when grown with chicory or perennial ryegrass, and (b) there is an optimal ratio of non-legume:legume in a pasture mix that maximises biological N 2 fixation. Methods Chicory or perennial ryegrass was grown as a monoculture, or in a mixture with either lucerne (alfalfa, Medicago sativa ) or subterranean clover ( Trifolium subterraneum ) at 25:75, 50:50 or 75:25 ratio (non-legume:legume based on plant numbers). Monocultures of lucerne and subterranean clover were included as controls. Results All treatments containing chicory extracted more mineral N from the soil than corresponding treatments containing perennial ryegrass. Subterranean clover %Ndfa was greater than lucerne. Combining lucerne with chicory in a 50:50 or 75:25 mixture increased the efficiency of N 2 fixation by > 20%. Growing chicory with subterranean clover in mixtures of 50:50 or 75:25 resulted in the highest %Ndfa for growth among all treatments ( P  < 0.05). However, the amounts of N 2 fixed by subterranean clover in the perennial ryegrass-subterranean clover mixture were similar to those in the chicory-subterranean clover mixture since dry matter accumulation from subterranean clover was higher when grown with perennial ryegrass. Conclusion The %Ndfa of legumes was greater when grown with chicory than perennial ryegrass. Chicory mixed with subterranean clover or lucerne in 50:50 ratios provided the optimum balance between legume dry matter yield and N 2 fixation.

[This corrects the article DOI: 10.1371/journal.pone.0262402.].

Legume cover crops in temperate cropping systems can fix substantial amounts of nitrogen (N) and reduce N fertiliser requirements for subsequent crops. However, little is known about potential biological N2 fixation by summer cover crop legumes in the short summer fallow in Mediterranean-type cropping systems. Six legume species (balansa clover, barrel medic, mung bean, sunn hemp, lablab and cowpea) were grown for 8–9 weeks in the field in semi-arid southern Australia during the summer fallow, and in a glasshouse experiment, to estimate N2 fixation using the 15N natural abundance method. Cowpea, sunn hemp and lablab produced 1.2–3.0 t ha−1 biomass in the field while balansa clover and barrel medic produced < 1.0 t ha−1. The percent of N derived from the atmosphere (%Ndfa) in the field ranged from 39% in barrel medic to 73% in sunn hemp, but only 15% (balansa clover) to 33% (sunn hemp) in the glasshouse experiment, likely due to higher soil mineral N availability in the glasshouse study. Biological N2 fixation of cowpea and sunn hemp in the field was 46–55 kg N ha−1, while N2 fixation in lablab and mung bean was lower (around 26 kg N ha−1). The N2 fixation in cowpea and sunn hemp of around 50 kg N ha−1 with supplementary irrigation in the field trial likely represents the upper limit of N contributions in the field in typically hot, dry summer conditions in Mediterranean-type climates. Given that any increase in summer cover crop biomass will have implications for water balances and subsequent cash crop growth, maximising N benefits of legume cover crops will rely on increasing the %Ndfa through improved rhizobium strains or inoculation technologies. This study provides the first known estimates of biological N2 fixation by legume cover crops in the summer fallow period in cropping systems in Mediterranean-type environments, providing a benchmark for further studies.

In many parts of the world, conditions for small scale agriculture are worsening, creating challenges in achieving consistent yields. The use of automated decision support tools, such as Bayesian Belief Networks (BBNs), can assist producers to respond to these factors. This paper describes a decision support system developed to assist farmers on the Mekong Delta, Vietnam, who grow both rice and shrimp crops in the same pond, based on an existing BBN. The BBN was previously developed in collaboration with local farmers and extension officers to represent their collective perceptions and understanding of their farming system and the risks to production that they face. This BBN can be used to provide insight into the probable consequences of farming decisions, given prevailing environmental conditions, however, it does not provide direct guidance on the optimal decision given those decisions. In this paper, the BBN is analysed using a novel, temporally-inspired data mining approach to systematically determine the agricultural decisions that farmers perceive as optimal at distinct periods in the growing and harvesting cycle, given the prevailing agricultural conditions. Using a novel form of data mining that combines with visual analytics, the results of this analysis allow the farmer to input the environmental conditions in a given growing period. They then receive recommendations that represent the collective view of the expert knowledge encoded in the BBN allowing them to maximise the probability of successful crops. Encoding the results of the data mining/inspection approach into the mobile Decision Support System helps farmers access explicit recommendations from the collective local farming community as to the optimal farming decisions, given the prevailing environmental conditions.

Vietnam’s Mekong River Delta (MRD), where rice is the dominant crop, is increasingly impacted by salinity intrusion, highlighting the need for alternative cropping options. This study evaluated the growth and yield performance of quinoa, beetroot, and maize under three irrigation salinity levels (0, 2 and 4 g/L), with and without rice straw mulch (7 t/ha), in greenhouse conditions representative of the MRD dry season. Agronomic traits, physiological parameters, and changes in soil, including electrical conductivity (ECe), soluble sodium (Sol-Na+), and exchangeable sodium percentage (ESP), were assessed. Results showed that quinoa demonstrated the greatest salinity tolerance, maintaining stable growth and yield under 4 g/L saline irrigation and soil ECe exceeding 15 dS/m. Beetroot’s yield was not significantly different under 2 g/L saline irrigation with straw mulching. Maize was highly sensitive to salinity and environmental stress, failing to complete its growth cycle under high heat and humidity, even in non-saline conditions. Across treatments, rice straw mulching significantly reduced soil ECe, Sol-Na+, and ESP, and improved crop performance under saline irrigation. Overall, quinoa and beetroot, especially when combined with mulching, offer promising alternatives for dry-season cropping in saline-prone areas of the MRD. In contrast, maize cultivation requires improved soil and environmental management under such conditions.

Australia’s southern cropping systems have limited plant diversity, dominated by cultivation of small grain winter cereals, mainly wheat (Triticum aestivum L) and barley (Hordeum vulgare L.), with a smaller proportion of break crops including canola (Brassica napus L.) and pulse legumes. Synchronous intercropping, where two cash crops are sown and grown together, and harvested simultaneously, could increase plant diversity but adds additional complexities in these highly mechanised farming systems. Temporary intercropping involves multiple plant species being sown together, with all but one species (the cash crop) terminated prior to harvest. This perspective explores temporary intercropping as a management practice to integrate a greater diversity of plant species into the cropping system. The impacts of temporary intercropping on cash crop growth, grain yields, soil health, and nitrogen cycling are reviewed. The ease with which temporary intercropping trials can be implemented through participatory farmer research is demonstrated via two case studies. We conclude that temporary intercropping holds promise as a means by which to introduce greater plant species diversity into Australian southern farming systems, but further research is needed to optimise intercrop species and seeding rates, fertiliser practices, and the timing of intercrop termination before economic assessments can be made.

The increasing impacts of water scarcity and salinity intrusion in the Mekong River Delta (MRD) pose significant challenges to sustainable agricultural production, particularly during the dry season. This study evaluated the potential of the Chameleon soil water sensor as a tool to improve irrigation management for upland crops cultivated on former rice fields in the MRD. Three independent trials were conducted: (1) laboratory‐based calibration for the sensor across three common soil textures of the MRD, (2) investigating the use of the Chameleon soil water sensor under varying salinity levels of irrigation water in the greenhouse condition, using beetroot ( Beta vulgaris L.) as a test crop, and (3) the field assessment integrating the sensor with straw mulching for beetroot under real‐world conditions. The results showed that the Chameleon soil water sensor demonstrated consistent sensitivity across sandy, clay loam, and silty clay soils, aligning well with van Genuchten‐modeled soil water retention curves. In greenhouse conditions, sensor‐guided irrigation reduced water use by 45.1%–53.8% compared to the farmer’s daily irrigation practice (the control) treatment across increasing salinity levels (0, 0.5, and 1.0 g L −1 ) of saline irrigating water, while maintaining comparable beetroot yields (up to 63.2 g pot −1 ) and significantly improving water use efficiency (WUE), reaching values up to 4.71 kg m −3 . The field trial showed that combining the sensor with mulching stabilized soil moisture, improved chlorophyll content (58.35 SPAD), and reduced total irrigation by over 60% compared to the control. These findings confirm the Chameleon sensor’s potential as a simple and practical tool for precision irrigation. Its integration with mulching offers a promising strategy for water conservation and salinity management in smallholder farming systems in the saline‐affected areas in the MRD and similar environments.

Aim To test for the presence of an impediment to water flow at the soil-root interface. Methods Wheat plants were grown in repacked and undisturbed field soil. Their transpiration rate, E, was varied in several steps from low to high and then back to low again, while the hydrostatic pressure in the leaf xylem, Ψ xylem , was measured non-destructively and continuously. These measurements were compared to a mathematical model that calculated Ψ xylem by assuming that the hydraulic resistance across the plant was constant and that the radial flow of water to unit length of a typical plant root generated gradients in pressure in the soil water. Results For the repacked soil, the radial flow model could not match the experiment during the falling phase of E, unless it was assumed that either an additional, constant, interfacial resistance between the soil and the roots had developed when E was large and Ψ xylem was rapidly falling, or that the resistance within the plant had changed. For the undisturbed field soil, the radial flow model did not agree with the experiment. Plausible agreement was achieved when plant water uptake was accounted for using a distributed sink model in HYDRUS-1D, with E integrated across the rootzone. This approach was based on the measured large variation in the vertical distribution of roots. Conclusions There was no strong evidence of large drawdowns of soil water in the rhizosphere, even when Ψ xylem was falling rapidly when E was large and the soil was moderately dry. Thus, there seems to have been an additional impediment to water flow from soil to plant, either within the plant, or at the interface between the two.

Aims To determine soil water difrusivity, D(θ), on undisturbed field soil at medium to low water content (suction range from 10 to 150 m of water), for the purpose of modeling the uptake of water by plant roots. Methods The method is based on the analysis of onestep outflow induced by a turbulent stream of dry air over the exposed end of a soil core, with the other end of the core enclosed. The outflow is measured through time as the change in the weight of the core as it sits on a recording balance. D(θ)is calculated by deconvoluting the measured outflow function. Results Over the suction range of 10 to 150 m of water, D(θ) calculated on the undisturbed soil ranged from 20×10⁻⁹ to 10×10⁻⁹ [m² S⁻¹], substantially higher than other published estimates over this range in suction. Conclusions These unusually large values cast doubt on the view that flow of water to roots limits uptake of water from the targeted subsoil.

Many inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey covering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle.