Assessing green manure impact on wheat productivity through Bayesian analysis of yield monitor data

Agronomy research traditionally relies on small, controlled trial plots, which may not accurately represent the complexities and variabilities found in larger, real-world settings. To address this gap, we introduce a Bayesian methodology for the analysis of yield monitor data, systematically collected across extensive agricultural landscapes during the 2020/21 and 2021/22 growing seasons. Utilizing advanced yield monitoring equipment, our method provides a detailed examination of the effects of green manure on wheat yields in a real-world context. The results from this comprehensive analysis reveal significant insights into the impact of green manure application on wheat production, demonstrating enhanced yield outcomes across varied landscapes. This evidence suggests that the Bayesian approach to analyzing yield monitor data can offer more precise and contextually relevant information than traditional experimental designs. This research underscores the value of integrating large-scale data analysis techniques in agronomy, moving beyond small-scale trials to offer a broader, more accurate perspective on agricultural practices. The adoption of such methodologies promises to refine farming strategies and policies, ultimately leading to more effective and sustainable agricultural outcomes. The inclusion of a Python script in the appendix illustrates our analytical process, providing a tangible resource for replicating and extending this research within the agronomic community.

Breeding has selected for architectural and photosynthetic traits in lentils

Genetic progress in seed yield in lentils (Lens culinaris Medik) has increased by 1.1% per year in Australia over the past 27 years. Knowing which plant traits have changed through breeding during this time can give important insights as to how lentil yield has increased. This study aims to identify morphological and physiological traits that were directly or indirectly selected between 1993 and 2020 in the Australian lentil breeding program using 2 years of experimental data. Major changes occurred in plant architecture during this period. Divergent selection has seen the release of varieties that have sprawling to very upright types of canopies. Despite this genetic diversity in recently released varieties, there is an overall tendency of recently released varieties having increased plant height and leaf size with reduced number of branches. Increased light interception was positively correlated with year of release (YOR) and yield, and likely results from indirect selection of yield and taller plant types. There is an indication that recently released varieties have lower CO₂ assimilation rate, stomatal conductance and canopy temperature depression (CTD) at high ambient temperatures (~30°C). Understanding lentil physiology will assist in identifying traits to increase yield in a changing climate with extreme weather events.

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

The demand for nitrogen (N) for crop production increased rapidly from the middle of the twentieth century and is predicted to at least double by 2050 to satisfy the on-going improvements in productivity of major food crops such as wheat, rice and maize that underpin the staple diet of most of the world's population. The increased demand will need to be fulfilled by the two main sources of N supply - biological nitrogen (gas) (N2) fixation (BNF) and fertilizer N supplied through the Haber-Bosch processes. BNF provides many functional benefits for agroecosystems. It is a vital mechanism for replenishing the reservoirs of soil organic N and improving the availability of soil N to support crop growth while also assisting in efforts to lower negative environmental externalities than fertilizer N. In cereal-based cropping systems, legumes in symbiosis with rhizobia contribute the largest BNF input; however, diazotrophs involved in non-symbiotic associations with plants or present as free-living N2-fixers are ubiquitous and also provide an additional source of fixed N. This review presents the current knowledge of BNF by free-living, non-symbiotic and symbiotic diazotrophs in the global N cycle, examines global and regional estimates of contributions of BNF, and discusses possible strategies to enhance BNF for the prospective benefit of cereal N nutrition. We conclude by considering the challenges of introducing in planta BNF into cereals and reflect on the potential for BNF in both conventional and alternative crop management systems to encourage the ecological intensification of cereal and legume production.

Photosynthetic and Photoprotective Responses to Steady-State and Fluctuating Light in the Shade-Demanding Crop Amorphophallus xiei Grown in Intercropping and Monoculture Systems

Photosynthetic and photoprotective responses to simulated sunflecks were examined in the shade-demanding crop Amorphophallus xiei intercropped with maize (intercropping condition) or grown in an adjacent open site (monoculture condition). Both intercropping leaves and monoculture leaves exhibited very fast induction responses. The times taken to achieve 90% maximum net photosynthetic rate in intercropping leaves and monoculture leaves were 198.3 ± 27.4 s and 223.7 ± 20.5 s during the photosynthetic induction, respectively. During an 8-min simulated sunfleck, the proportion of excess excited energy dissipated through the xanthophyll cycle-dependent pathway (Φ NPQ) and dissipated through constitutive thermal dissipation and the fluorescence (Φ f, d) pathway increased quickly to its maximum, and then plateaued slowly to a steady state in both intercropping and monoculture leaves. When the illumination was gradually increased within photosystem II (PSII), Φ NPQ increased quicker and to a higher level in monoculture leaves than in intercropping leaves. Relative to their monoculture counterparts, intercropping leaves exhibited a significantly lower accumulation of oxygen free radicals, a significantly higher content of chlorophyll, and a similar content of malondialdehyde. Although monoculture leaves exhibited a larger mass-based pool size of xanthophyll cycle [V (violaxanthin) + A (antheraxanthin) + Z (zeaxanthin)] than intercropping leaves, intercropping leaves had a higher ratio of (Z + A)/(V + Z + A) than monoculture leaves. intercropping leaves had markedly higher glutathione content and ascorbate-peroxidase activity than their monoculture counterparts. Similar activities of catalase, peroxidase, dehydroascorbate reductase, and monodehydroascorbate were found in both systems. Only superoxide dismutase activity and ascorbate content were lower in the intercropping leaves than in their monoculture counterparts. Overall, the xanthophyll cycle-dependent energy dissipation and the enzymatic antioxidant defense system are important for protecting plants from photooxidation in an intercropping system with intense sunflecks.

Soil mineral nitrogen benefits derived from legumes and comparisons of the apparent recovery of legume or fertiliser nitrogen by wheat

Nitrogen (N) contributed by legumes is an important component of N supply to subsequent cereal crops, yet few Australian grain-growers routinely monitor soil mineral N before applying N fertiliser. Soil and crop N data from 16 dryland experiments conducted in eastern Australia from 1989–2016 were examined to explore the possibility of developing simple predictive relationships to assist farmer decision-making. In each experiment, legume crops were harvested for grain or brown-manured (BM, terminated before maturity with herbicide), and wheat, barley or canola were grown. Soil mineral N measured immediately before sowing wheat in the following year was significantly higher (P < 0.05) after 31 of the 33 legume pre-cropping treatments than adjacent non-legume controls. The average improvements in soil mineral N were greater for legume BM (60 ± 16 kg N/ha; n = 5) than grain crops (35 ± 20 kg N/ha; n = 26), but soil N benefits were similar when expressed on the basis of summer fallow rainfall (0.15 ± 0.09 kg N/ha per mm), residual legume shoot dry matter (9 ± 5 kg N/ha per t/ha), or total legume residue N (28 ± 11%). Legume grain crops increased soil mineral N by 18 ± 9 kg N/ha per t/ha grain harvested. Apparent recovery of legume residue N by wheat averaged 30 ± 10% for 20 legume treatments in a subset of eight experiments. Apparent recovery of fertiliser N in the absence of legumes in two of these experiments was 64 ± 16% of the 51–75 kg fertiliser-N/ha supplied. The 25 year dataset provided new insights into the expected availability of soil mineral N after legumes and the relative value of legume N to a following wheat crop, which can guide farmer decisions regarding N fertiliser use.

Enhancing Non-symbiotic N2 Fixation in Agriculture

Much of the demand for nitrogen (N) in cereal cropping systems is met by using N fertilisers, but the cost of production is increasing and there are also environmental concerns. This has led to a growing interest in exploring other sources of N such as biological N2fixation. Non-symbiotic N2fixation (by free-living bacteria in soils or associated with the rhizosphere) has the potential to meet some of this need especially in the lower input cropping systems worldwide. There has been considerable research on non-symbiotic N2fixation, but still there is much argument about the amount of N that can potentially be fixed by this process largely due to shortcomings of indirect measurements, however isotope-based direct methods indicate agronomically significant amounts of N2fixation both in annual crop and perennial grass systems. New molecular technologies offer opportunities to increase our understanding of N2-fixing microbial communities (many of them non-culturable) and the molecular mechanisms of non-symbiotic N2fixation. This knowledge should assist the development of new plant-diazotrophic combinations for specific environments and more sustainable exploitation of N2-fixing bacteria as inoculants for agriculture. Whilst the ultimate goal might be to introduce nitrogenase genes into significant non-leguminous crop plants, it may be more realistic in the shorter-term to better synchronise plant-microbe interactions to enhance N2fixation when the N needs of the plant are greatest. The review explores possibilities to maximise potential N inputs from non-symbiotic N2fixation through improved management practices, identification of better performing microbial strains and their successful inoculation in the field, and plant based solutions.

Tropical legume crop rotation and nitrogen fertilizer effects on agronomic and nitrogen efficiency of rice

Bush bean, long bean, mung bean, and winged bean plants were grown with N fertilizer at rates of 0, 2, 4, and 6 g N m⁻² preceding rice planting. Concurrently, rice was grown with N fertilizer at rates of 0, 4, 8, and 12 g N m⁻². No chemical fertilizer was used in the 2nd year of crop to estimate the nitrogen agronomic efficiency (NAE), nitrogen recovery efficiency (NRE), N uptake, and rice yield when legume crops were grown in rotation with rice. Rice after winged bean grown with N at the rate of 4 g N m⁻² achieved significantly higher NRE, NAE, and N uptake in both years. Rice after winged bean grown without N fertilizer produced 13–23% higher grain yield than rice after fallow rotation with 8 g N m⁻². The results revealed that rice after winged bean without fertilizer and rice after long bean with N fertilizer at the rate of 4 g N m⁻² can produce rice yield equivalent to that of rice after fallow with N fertilizer at rates of 8 g N m⁻². The NAE, NRE, and harvest index values for rice after winged bean or other legume crop rotation indicated a positive response for rice production without deteriorating soil fertility.

How a phosphorus-acquisition strategy based on carboxylate exudation powers the success and agronomic potential of lupines (Lupinus, Fabaceae)

Lupines (Lupinus species; Fabaceae) are an ancient crop with great potential to be developed further for high-protein feed and food, cover crops, and phytoremediation. Being legumes, they are capable of symbiotically fixing atmospheric nitrogen. However, Lupinus species appear to be nonmycorrhizal or weakly mycorrhizal at most; instead some produce cluster roots, which release vast amounts of phosphate-mobilizing carboxylates (inorganic anions). Other lupines produce cluster-like roots, which function in a similar manner, and some release large amounts of carboxylates without specialized roots. These traits associated with nutrient acquisition make lupines ideally suited for either impoverished soils or soils with large amounts of phosphorus that is poorly available for most plants, e.g., acidic or alkaline soils. Here we explore how common the nonmycorrhizal phosphorus-acquisition strategy based on exudation of carboxylates is in the genus Lupinus, concluding it is very likely more widespread than generally acknowledged. This trait may partly account for the role of lupines as pioneers or invasive species, but also makes them suitable crop plants while we reach "peak phosphorus".

Liming and choice of pasture species improve rhizobial persistence in an acidic chromosol (red-brown earth)

An experiment was conducted to determine the persistence of soil root-nodule bacteria as influenced by different rates of lime and the previous pasture species. The work was done at Condobolin, central-western New South Wales, on a chromosol (red-brown earth), acidic in the upper profile (pHCa 4.6), which was representative of soils for an extensive region of the eastern Australian wheat belt. In autumn 1997, the experimental area was treated with 4 rates (6.0 t/ha, 3.0 t/ha, 1.5 t/ha, nil) of finely-ground agricultural limestone and sown with 5 pasture species: lucerne (Medicago sativa), barrel medic (M. truncatula), subterranean clover (Trifolium subterraneum), rose clover (T. hirtum) and ryegrass (Lolium rigidum). The pastures were removed with herbicide and cultivation in September 2000. The land lay fallow for 9 months and then was sown to wheat (Triticum aestivum) in autumn 2001 and again in autumn 2002. The most probable numbers of soil (0–10 cm) populations of the root–nodule bacterium for Medicago species (Sinorhizobium meliloti) and for the Trifolium species (Rhizobium leguminosarum bv. trifolii) were counted in May 2001 and May 2002. Soil pH, which was significantly (P<0.05) elevated 12 months after liming, declined substantially during the next 4 years although there was no concomitant decline in the pH of unlimed soil. The pasture species were highly productive of both pasture dry matter and nitrogen. The majority of legume pasture nitrogen was a consequence of symbiotic nitrogen fixation. There was a small but significant (P<0.05) dry matter response to application of lime in lucerne and barrel medic, and a larger nitrogen response to liming in lucerne, barrel medic and rose clover. Nitrogen fixation by rose clover appeared suboptimal. It was assumed from the density of plants that large populations of rhizobia developed in the soil during the growth of the legumes. Nine months after removal of the pasture, rhizobia numbers had fallen to low levels but did not fall further during the following year. The initial fall was attributed to high soil temperatures and low soil moisture during the Condobolin summer. The population of rhizobia for Trifolium species was about twice that of the rhizobia for Medicago species but the difference was not statistically significant. Liming had an overriding influence on the size of rhizobial populations, except in plots that had previously grown ryegrass where numbers remained low irrespective of rate of liming. Overall, most probable numbers escalated with each increase in rate of liming, from 10/g soil in the nil lime plots to 708/g in the 6 t/ha lime plots. The rhizobial homology of the pasture species (i.e. Sinorhizobium meliloti for the Medicago species and Rhizobium leguminosarum bv. trifolii for the Trifolium species) had an underlying but major influence on most probable numbers and in determining which rhizobial species occurred more commonly. Estimated populations of rhizobia in soils from homologous legumes were about 8 times those found in soils from non-homologous legumes. The benefits of applying lime to this red-brown earth soil may not have been merely a consequence of correction of low soil pH; increased levels of calcium may also have had a role. The results are discussed in relation to re-establishment of legume leys after the cereal phase of the cropping system.

Productivity, sustainability, and rainfall-use efficiency in Australian rainfed Mediterranean agricultural systems

Mediterranean environments are characterised by hot, dry summers and cool, wet winters. The native vegetation in Mediterranean-climatic regions is predominantly perennial shrubs and trees intermixed with annual forbs. In south-western Australia, the spread of agriculture has seen the well adapted perennial vegetation replaced by rainfed annual crops and pastures. This has increased waterlogging and secondary salinity, thereby causing loss of productivity in ~10% of the cleared land area. To reduce deep drainage and make the agricultural systems environmentally sustainable requires the re-introduction of perennial vegetation in the form of belts of trees or shrubs, and phase-farming systems with perennials such as lucerne replacing annual pastures between the cropping years. To be economically viable, agricultural productivity needs to increase by at least 3% per annum. Yields of dryland wheat, the predominant crop in the Mediterranean agricultural regions of Australia, have increased at ~1%/year for the century preceding the 1980s and since then by nearly 4%/year. Increases have arisen from both genotypic and agronomic improvements. Genotypic increases have arisen from selection for earliness, early vigour, deep roots, osmotic adjustment, increased transpiration efficiency, improved disease resistance, and an improved harvest index from high ear weight (grain number) at flowering and high assimilate storage and remobilisation. Agronomic increases have arisen from early sowing that has been enabled by minimum tillage, increased fertiliser use, especially nitrogen, weed control, and rotations to improve weed control, minimise disease risk, and increase nitrogen availability. Evidence is presented suggesting that the rapid increase in yield of wheat in the last two decades has likely arisen from the rapid adoption of new technologies. For productivity to be maintained in the face of the increasing requirement to be environmentally sustainable will be a challenge and will require better integration of breeding and agronomy.

Grain yield production in relation to plant growth of wheat and canola following clover pastures in southern Victoria

The plant growth and grain yield of crops following a pasture phase in 1:1 pasture–crop rotations were studied in southern Victoria in 2001 (wheat and canola at Hamilton, and wheat at Streatham and Gnarwarre). Both the wheat and canola crops produced high grain yields with no application of nitrogen fertiliser. In experiment 1 (at Hamilton) where the crops were dependent on nitrogen input from subterranean clover pasture, canola produced 4.1 t/ha of grain and wheat averaged 6.0 t/ha. The 3 canola cultivars (Charlton, Mystic and Surpass 400) had similar grain yields. However, for wheat, the late-maturing spring wheat cv. Kellalac and the early-maturing spring wheat cv. Silverstar produced significantly higher grain yields (6.6 and 6.3 t/ha, respectively) than the late-maturing winter cv. Brennan (5.0 t/ha). The 3 cultivars of each crop differed markedly in their major yield components. The most striking differences were those shown by Silverstar, which had the highest yield, together with Kellalac, but had lower biomass and lower leaf area index than the 2 late-maturing wheats. Silverstar compensated by having 50% more grains per head than the late-maturing Brennan. While Silverstar flowered on average 34 days earlier than the 2 other wheats, it took some 3 weeks longer to mature after anthesis. In experiment 2, the wheat crop (cv. Silverstar) produced grain yields of 5.4 t/ha over 6 different treatments, with higher grain yields at Streatham (6.1 t/ha) than at Gnarwarre (4.7 t/ha). Across the 2 sites, the grain yields following clovers reached over 5.7 t/ha, in contrast with low grain yields from the continuous crop (3.7 t/ha) and fallow/crop treatments (3.7 t/ha). Grain yields were closely related to the herbage dry matter production of previous pasture legumes, indicating a positive crop response. This may, in turn, reflect the nutrient status of the treatments, particularly the nitrogen status.

Crop rotation effect on wheat grain yield as mediated by changes in the degree of water and nitrogen co-limitation

Theoretically, growth of stressed plants is maximised when all resources are equally limiting. The concept of co-limitation could be used to integrate key factors affected by crop rotation. This paper tested the hypothesis that the effect of crop rotation on the yield of wheat is partially mediated by changes in the degree of co-limitation between nitrogen and water. Four rotations were established on a sodic, supracalcic, red chromosol in a Mediterranean-type environment of southern Australia. Rotations included wheat grown after (a) faba bean harvested for grain, (b) faba bean incorporated as green manure, (c) ryegrass pasture, or (d) medic pasture; barley was grown after wheat in all cases. The response of wheat to the rotations during 3 growing seasons was analysed in terms of nitrogen and water co-limitation, and the response of barley was taken as a measure of the persistence of rotation effects. Daily scalars quantifying water and nitrogen stress effects on tissue expansion were calculated with a crop simulation model. These scalars were integrated in a series of seasonal indices to quantify the intensity of water (SW ) and nitrogen stress (SN ), the aggregated intensity of water and nitrogen stress (SWN ), the degree of water and nitrogen co-limitation (CWN ), and the integrated effect of stress and co-limitation (SCWN 25 CWN/SWN ). The expectation is that grain yield should be inversely proportional to stress intensity and directly proportional to degree of co-limitation, thus proportional to SCWN . Combination of rotations and seasons generated a wide variation in the amount of water and inorganic nitrogen in the 1-m soil profile at the time of wheat sowing. Plant-available water ranged from 33 to 107 mm, and inorganic nitrogen from 47 to 253 kg N/ha. Larger amounts of nitrogen were found after green-manured faba bean, and smaller after grass pasture. There was a consistent effect of rotation on wheat yield and grain protein content, which persisted in subsequent barley crops. Measured grain yield of wheat crops ranged from 2.5 to 4.8 t/ha. It was unrelated to water or nitrogen stresses taken individually, inversely related to the aggregated stress index SWN , and directly related to the CWN index of co-limitation. The combination of stress and co-limitation in a single index SCWN accounted for 65% of the variation in measured crop yield. This is a substantial improvement with respect to the stress effect quantified with SWN , which accounted for 43% of yield variation. It is concluded that rotation effects mediated by changes in the relative availability of water and nitrogen can be partially accounted for by degree of resource co-limitation.