Negative Yield Response Research Articles

Profitability of foliar fungicides in double crop soybean under low-disease environments

Double-crop soybean production involves planting soybean (Glycine max) directly following winter wheat (Triticum aestivum) harvest. Frogeye leaf spot (FLS), caused by Cercospora sojina, is an important late-season foliar disease affecting soybean fields in the United States. In some instances, foliar fungicides have been used in double-crop soybean production with little to no FLS present, raising questions on the profitability of these applications. This study analyzed yield data from 25 fungicide trials across five states (Illinois, Indiana, Kentucky, Missouri, and Tennessee) conducted under low FLS pressure, from 2008 to 2021, on double-crop soybean. Fungicide classes evaluated in the trials included quinone outside inhibitors (QoI), demethylation inhibitors (DMI), and methyl benzimidazole carbamates (MBC) applied alone, and mixtures of chemistry classes that included DMI+succinate dehydrogenase inhibitor (SDHI), MBC+DMI, QoI+DMI, and QoI+DMI+SDHI. A network meta-analytic model estimated yield differences between fungicide-treated and nontreated plots, which ranged from -28 to 72 kg/ha among the fungicide treatments. Negative yield response values were estimated for the single fungicide classes MBC (-15.7 kg/ha) and QoI (-28.4 kg/ha). Yield difference as high as 72.8 kg/ha was estimated only for DMI+SDHI. Economic analyses indicated that, due to the lower yield responses, probabilities of breaking even were lower than 50% for all fungicide treatments, regardless of the fungicide cost or soybean sale price. Therefore, the low yield responses associated with foliar fungicides in low-disease environments linked to the higher risk of not offsetting the costs, suggest that growers should consider disease risk prior to making the fungicide application.

Rising temperatures can negate CO2 fertilization effects on global staple crop yields: A meta-regression analysis

Many meta-analyses have reported increased seed yields in response to rising carbon dioxide concentrations ([CO2]) or decreased yields in response to warming temperatures, but synthesis of their concurrent effects is lacking. We conducted an extensive meta-regression analysis of wheat, rice, soybean, and maize seed yield responses to simultaneous increases in [CO2] and temperature and examined the sensitivity of potential yields to levels projected for mid- and late-century periods using CMIP6 climate model outputs. Positive linear yield responses to increasing [CO2] were observed in maize, rice, and soy, with slopes ranging from +4 % - (100 µmol mol−1) -1 in rice to +10 % - (100 µmol mol−1) -1 in soy. In contrast, wheat yield response to increasing [CO2] was not linear, instead flattening by +200 µmol mol−1 of CO2 elevation. Negative linear yield responses to warming were modeled for the three cereal crops, with slopes of −7.6% -°C −1 in wheat and −9.5% -°C −1 in rice and maize. Soy yield did not decrease with increasing warming treatments in this analysis, but experimental warming treatments did not exceed optimal soy growth temperature ranges. Across the three crops with available observations, yield responses were significantly lower in Free-Air CO2 Enrichment than in studies using other fumigation methods, likely due to the associated rapid fluctuations in [CO2]. Considering potential future eC and eT levels simultaneously, we find that eC fertilization effects on seed yield will likely be greatly reduced or entirely negated in the major crops maize, rice, and wheat. Net yield responses to concurrent [CO2] and temperature increases should not be based on limited observations of responses to either factor in isolation, because the levels of each factor as well as experimental conditions influence responses.

Response of wheat and maize yields to different tillage practices across China: A meta-analysis

Tillage practice can change soil properties, regulate crop root development and nutrient availability, thus affecting crop growth and yield. However, the effect of no tillage (NT) and deep tillage (DT) on crop yield relative to conventional tillage (CT) under varied environmental and management conditions is unclear in China. We assessed the yield response of wheat and maize to NT and DT relative to CT based on collected field data (518 observations) with a meta-analysis. In general, NT led to negative yield response of both crops relative to CT, whereas maize presented a positive yield response (6.0 %) to NT in sandy soil, and crop yield responses to NT were not significantly different among environmental and management factors. DT significantly increased the yield of wheat (8.7 %) and maize (8.2 %) over CT. For wheat, the yield response to DT was similar across soil textures, climate conditions, experiment durations, N fertilizer rates, and residue managements; however, the interval DT every 2–3 years (13.2 %) and monoculture (13.9 %) increased yield response than the continuous DT (8.4 %) and double cropping system (8.9 %), respectively. The yield response of maize to DT was greater in semidry region (16.1 %) and under high N fertilizer rate (>300 kg N ha−1) (16.1 %), interval DT (12.4 %) compared with those in humid (7.5 %) and semi-humid (6.8 %) regions, low N fertilizer rates (<300 kg N ha−1) (6.9 %−7.5 %), and continuous DT (7.8 %), respectively; but other environmental and management factors did not affect its yield response. Overall, NT presented similar yield of wheat and maize to CT, while DT significantly enhanced their yields; this analysis revealed the crucial environmental and management factors influencing yield response to tillage practices in China, we also gave some suggestions on selecting appropriate tillage methods to realize high crop yield or/and agricultural sustainable development.

Ameliorating alkaline dispersive subsoils with organic amendments: Are productivity responses due to nutrition or improved soil structure?

Background and aimsAlkaline dispersive subsoils are characterised by multiple physicochemical constraints that limit plant water and nutrient acquisition. Subsoil amelioration through organic amendments (OAs) requires significant financial investment. Whereas large yield responses can result following amelioration, sometimes small or even negative yield responses can occur, resulting in a significant net financial loss for the farmer. For farmers to feel confident in investing in subsoil amelioration better prediction of the likely yield improvement is required and to achieve this an understanding of the underlying mechanisms such as nutritional and non-nutritional drivers, and the longevity of benefits are required. Our study aimed to ascertain the drivers of yield improvements from subsoil amelioration with OAs.MethodsIn a controlled environment, wheat (Triticum aestivum L. cv. Scepter) plants were grown until maturity in a Solonetz amended with (i) poultry litter (PL; 20 t ha−1), and (ii) NPKS nutrients and (iii) model organic carbon (MOC) with equivalent amounts of nutrients and total carbon contained in the PL, and (iv) NPKS + MOC. Control (no amendments) and gypsum (5 t ha−1) were included as district practices. Before planting, amendments were applied as a vertical band at 20 – 40 cm depth and pre-incubated. Plant biomass, grain yield, root biomass, and physicochemical properties of the soil associated with the amendment band were quantified at harvest.ResultsCompared to the control, wheat grain yield was increased by 30% for PL, 43% for NPKS + MOC, and 61% for NPKS, but no differences in yield were detected for MOC or gypsum. The lower yield increase by PL than NPKS with or without MOC was likely due to the readily available form of plant nutrients in the inorganic fertilisers vs slower mineralisation of nutrients from the OAs. Improvement in soil physicochemical properties following amelioration of alkaline dispersive subsoil resulted in better root proliferation and subsoil water use. Grain yield showed a positive correlation with root biomass in the subsoil layers.ConclusionsIn the short-term (one crop cycle), organic amendments improved soil’s non-nutritional physical and chemical properties but had no additional nutritional effect on wheat grain yield compared to inorganic fertiliser application. Longer-term studies are needed to determine the legacy effect of the nutritional contribution in conjunction with the improvement of soil structure from the OAs in alkaline dispersive subsoils.

Sorghum (Sorghum bicolor L.) yield response to rainwater harvesting practices in the semi-arid farming environments of Zimbabwe: A meta-analysis

Rainwater harvesting practices are increasingly gaining recognition as viable adaptation strategies to overcome rainfall variability caused by climate change in semi-arid regions of Zimbabwe. A meta-analysis was conducted to provide a comprehensive quantitative synthesis of biophysical conditions (rainfall, soil texture, N fertility, mulch) under which basins, rippers, and tied ridges affected sorghum yields in semi-arid areas of Zimbabwe. Rainfall amount (<600 mm, 600–1000 mm), soil texture (20 % clay, 20–35 % clay), mulch (basin + mulch, ripper + mulch, tied ridges + mulch), and fertility (0–30 kg N/ha, 30–100 kg N/ha) were used to evaluate the response of sorghum grain yield to rainwater harvesting practices. Grain yield response was compared to the control (conventional practice) using the weighted mean yield difference approach. The results showed comparable sorghum grain yields in all the rainwater harvesting practices across the biophysical conditions, except under rainfall and soil textural classes. Tied ridges had a significant (p < 0.05) negative sorghum grain yield response (−0.25 t/ha) under <600 mm of rainfall, while ripper planting resulted in a substantial negative grain yield response (−0.32 t/ha) under 600–1000 mm of rainfall. Ripper planting reduced grain yield significantly (p < 0.05) (−1.06 t/ha) in soils with 20–35% clay. The results suggest that basins, rippers, and tied ridges did not improve sorghum grain yield across all agronomic conditions.

Impacts of compound hot–dry extremes on US soybean yields

Abstract. The US agriculture system supplies more than one-third of globally traded soybean, and with 90 % of US soybean produced under rainfed agriculture, soybean trade is particularly sensitive to weather and climate variability. Average growing season climate conditions can explain about one-third of US soybean yield variability. Additionally, crops can be sensitive to specific short-term weather extremes, occurring in isolation or compounding at key moments throughout crop development. Here, we identify the dominant within-season climate drivers that can explain soybean yield variability in the US, and we explore the synergistic effects between drivers that can lead to severe impacts. The study combines weather data from reanalysis and satellite-informed root zone soil moisture fields with subnational crop yields using statistical methods that account for interaction effects. On average, our models can explain about two-thirds of the year-to-year yield variability (70 % for all years and 60 % for out-of-sample predictions). The largest negative influence on soybean yields is driven by high temperature and low soil moisture during the summer crop reproductive period. Moreover, due to synergistic effects, heat is considerably more damaging to soybean crops during dry conditions and is less problematic during wet conditions. Compounding and interacting hot and dry (hot–dry) summer conditions (defined by the 95th and 5th percentiles of temperature and soil moisture respectively) reduce yields by 2 standard deviations. This sensitivity is 4 and 3 times larger than the sensitivity to hot or dry conditions alone respectively. Other relevant drivers of negative yield responses are lower temperatures early and late in the season, excessive precipitation in the early season, and dry conditions in the late season. We note that the sensitivity to the identified drivers varies across the spatial domain. Higher latitudes, and thus colder regions, are positively affected by high temperatures during the summer period. On the other hand, warmer southeastern regions are positively affected by low temperatures during the late season. Historic trends in identified drivers indicate that US soybean production has generally benefited from recent shifts in weather except for increasing rainfall in the early season. Overall, warming conditions have reduced the risk of frost in the early and late seasons and have potentially allowed for earlier sowing dates. More importantly, summers have been getting cooler and wetter over the eastern US. Nevertheless, despite these positive changes, we show that the frequency of compound hot–dry summer events has remained unchanged over the 1946–2016 period. In the longer term, climate models project substantially warmer summers for the continental US, although uncertainty remains as to whether this will be accompanied by drier conditions. This highlights a critical element to explore in future studies focused on US agricultural production risk under climate change.

Plant Functional Types Differ in Their Long-term Nutrient Response to eCO2 in an Extensive Grassland

Increasing atmospheric CO2 enhances plant biomass production and may thereby change nutrient concentrations in plant tissues. The objective of this study was to identify the effect of elevated atmospheric CO2 concentrations on nutrient concentrations of grassland biomass that have been grown for 16 years (1998–2013). The grassland biomass grown at the extensively managed Giessen FACE experiment, fumigated with ambient and elevated CO2 (aCO2; eCO2; +20%) was harvested twice annually. Concentrations of C, N, P, K, Ca, Mg, Mn, Fe, Cu and Zn were determined separately for grasses, forbs and legumes. Under eCO2, the concentration of N was reduced in grasses, Ca was reduced in grasses and forbs, P was reduced in grasses but increased in legumes, Mg concentration was reduced in grasses, forbs and legumes and K was reduced in grasses but increased in forbs. The nutrient yield (in g nutrient yield of an element per m−2) of most elements indicated negative yield responses at a zero biomass response to eCO2 for grasses. K and Zn nutrient yields responded positively to eCO2 in forbs and Mn and Fe responded positively in forbs and legumes. The results suggest that under eCO2 the nutrient concentrations were not diluted by the CO2 fertilization effect. Rather, altered plant nutrient acquisitions via changed physiological mechanisms prevail for increased C assimilation under eCO2. Furthermore, other factors such as water or nutrient availability affected plant nutrient concentrations under eCO2.

Effect of glyphosate application time on yield parameters of South African glyphosate-resistant maize cultivars

Glyphosate is the most used herbicide in South Africa. Due to observations by some South African maize producers that the application of glyphosate to glyphosate-resistant (GR) maize cultivars resulted in reduced yield, we conducted an in-depth study under local conditions. Through field trials, over two seasons (2017/2018 and 2018/2019), we investigated whether the application time of glyphosate would impact maize yields negatively. Various yield parameters were measured subsequent to glyphosate application to the local GR maize cultivars DKC74-74BR, DKC78-79BR, KKS4581, KKS8408, BG5785BR, PAN6R-710BR, P1814R and P2880WBR. Four glyphosate products were included (Roundup PowerMax®; Slash Plus 540 SL; TouchdownForte® and MambaTM DMA 480 SL), resulting in 32 cultivar x glyphosate product combinations. Each product was applied at V4, V4+V6, V6 and V8 growth stages together with an untreated control. Yield parameters measured (ears per plant, rows per ear, kernels per row, thousand kernel mass and yield) were expressed as a percentage of the control. The trials were planted as randomised complete block designs with three replicates. Limited response was observed with all the parameters investigated, with a significant negative yield response, greater than the untreated control, observed in only 3.1% of the cultivar x glyphosate product combinations evaluated. No clear trends or discernible and consistent impacts on yield and yield parameters could be established based on the application time of glyphosate (within label recommendations) across seasons. The findings contribute significantly to the knowledge base and current understanding of the international community and local producers alike regarding the effective use of glyphosate and generic variations thereof in crops of diverse genetic backgrounds.Significance:&#x0D; &#x0D; Limited response in the yield parameters evaluated were obtained in response to the application time (V4, V4+V6, V6 and V8) of the four glyphosate products on eight GR maize cultivars tested (p=0.1).&#x0D; Inconsistent patterns or trends were detected in cases where significance was obtained, implying that it would not be possible to draw accurate conclusions or formulate recommendations.&#x0D; Application time of glyphosate did not result in a significant reduction in yield compared to the untreated control, in the majority of the cultivar x glyphosate product combinations investigated, confirming that glyphosate application conducted within label specifications would not reduce yield, irrespective of the glyphosate product or genetic background of maize. &#x0D;

Is starter phosphorus fertilizer necessary for corn grown on Atlantic Coastal Plain soils?

AbstractProducers managing Coastal Plain soils in Maryland have reported visual symptoms of P deficiency in corn (Zea mays L.) grown on soils with P concentrations above the agronomic optimum range (e.g., 40–84 mg kg–1 Mehlich 3‐extractable phosphorus [M3P]). Yet, corn yield response to starter P fertilizer on soils with M3P concentrations above this range has not been consistently demonstrated in the literature. The objective of this study was to evaluate corn yield response to application of starter P fertilizer to soils with varying M3P concentrations. This study was conducted at three locations in Maryland where, following 14 yr of phytoremediation by continuous cropping and no P applications, M3P concentrations ranged from 34 to 237 mg kg–1 in soil samples collected from plots prior to study commencement. Beginning in 2015, half of each main plot received inorganic P application prior to corn planting in 3 yr, with corn yield measured in each split plot in each year. We observed no interaction effect of starter P fertilizer and soil P category on corn yield at any location. When the data were analyzed by site‐year, we observed no interaction effect, an effect of soil P category in 5 of 9 site‐years, and a yield response to starter fertilizer in 2 of 9 site‐years, with a positive yield response in 1 site‐year and a negative yield response in the other. Based on these results, we do not recommend Mid‐Atlantic farmers invest in starter P fertilization for corn grown on Coastal Plain soils when not recommended by soil testing.

Biological control in lucerne crops can negatively affect the development of root morphology, forage yield and quality

Root diseases of lucerne (Medicago sativa L.) play a significant role in reducing the persistence and productivity of stands; however, the potential of using biological control in lucerne crops has not yet been investigated. Our objectives were to determine the effect of biological crop protection on (i) lucerne plant density and root traits development and (ii) lucerne forage yield and nutritive value in a two-year field experiment. The lucerne stand was managed under three treatments of disease control: an untreated control and spraying with either Albit (hydrolysate of microorganisms containing microelements and poly-beta-hydroxy butyric acid) or Polyversum (mycoparasitic Pythium oligandrum) under five-cut utilization. Application of Albit resulted in a negative yield response, associated with a reduction of root branching, and it also reduced crude protein and increased crude fibre and water-soluble carbohydrates in the second cut of the first year of the experiment. Polyversum increased the percentage of infected plants relative to the control in the last year of the experiment. The study highlights that biological control of lucerne under field conditions may not always be beneficial because of the complex interactions between plant, biological preparation, and environment.

Soil‐Test Biological Activity with the Flush of CO2: IV. Fall‐Stockpiled Tall Fescue Yield Response to Applied Nitrogen

Core Ideas Soil biological activity is a reliable indicator of soil nitrogen availability. Nitrogen fertilization of fall stockpiled tall fescue should be adjusted based on soil testing. The flush of CO2 is a robust indicator of soil biological activity. A new paradigm of soil testing based on soil biological activity is possible. Fall stockpiling of tall fescue (Lolium arundinaceum) in the southeastern United States is promoted as an ecologically favorable cattle management approach to avoid the financial and environmental burdens of winter hay feeding. We hypothesized that soil N mineralization should be an important factor controlling forage yield response to N fertilizer. We conducted 55 N fertilizer trials in combination with analyses of soil C and N fractions at multiple locations in Georgia, North Carolina, Virginia, and West Virginia during two seasons. Plant‐available N, as a combination of residual inorganic N + mineralizable N at depth of 0 to 10 cm, was significantly negatively related with extent of forage dry matter response to N fertilizer input. Large variations in economically optimum N fertilizer requirement (EONR) occurred among fields, but when several fields were averaged along a gradient of soil biological activity, a strong negative yield response with increasing soil‐test biological activity emerged. With moderate soil‐test biological activity of 200 mg CO2–C kg–1 soil 3 d–1, EONR was 20 kg N Mg–1 forage dry matter (a value similar to current N fertilizer recommendations). However, with progressively greater soil‐test biological activity up to 600 mg CO2–C kg–1 soil 3 d–1, EONR declined in a nonlinear manner to near zero. These results illustrate that N fertilizer recommendations for fall stockpiled tall fescue pastures should be a function of soil‐test biological activity as an indicator of biologically active N. Greater economic and environmental sustainability would likely be attainable with a shift to recognizing soil biological activity in an ecologically oriented fertilization paradigm.

Perceptions of Midwestern Crop Advisors and Growers on Foliar Fungicide Adoption and Use in Maize.

Foliar fungicide use in hybrid maize in the United States was rare before 2000. The decade from 2000 to 2010 saw foliar fungicides increasingly applied to maize in the absence of appreciable disease pressure, a practice seemingly at odds with integrated pest management philosophy. Yet, it is commonly believed that growers do not employ management strategies unless there are perceived benefits. Maize (corn) growers (CGs) and certified crop advisors (CCAs) across four Midwestern states (Iowa, Illinois, Ohio, and Wisconsin) were surveyed to better understand their practices, values and perceptions concerning the use of foliar fungicides during 2005 to 2009. The survey results demonstrated the rapid rise in maize foliar fungicide applications from 2000 through 2008, with 84% of CGs who sprayed having used a foliar fungicide in maize production for the very first time during 2005 to 2009. During 2005 to 2009, 73% of CCAs had recommended using a foliar fungicide, but only 35% of CGs sprayed. Perceived yield gains, conditional on having sprayed, were above the break-even point on average. However, negative yield responses were also observed by almost half of CCAs and a quarter of CGs. Hybrid disease resistance was a more important factor to economically successful maize production than foliar fungicides. Diseases as a yield-limiting factor were more important to CGs than CCAs. As a group, CGs were not as embracing of foliar fungicide as were CCAs, and remained more conservative about the perceived benefits to yield.

Spatial analysis of dairy yields response to intensive farming in New Zealand

PurposeThe New Zealand (NZ) dairy industry faces the challenge of increasing productivity and dealing with public concerns over nutrient pollution. The effective policy needs to address regional differences in productivity and fertilizer use. The purpose of this paper is to investigate how spatial effects influence the relationship between dairy yields and intensive farming practices across regions in NZ.Design/methodology/approachThis paper employs spatial panel data models to establish whether unobserved spatial effects exist in the relationship between dairy yields and nutrient inputs regionally and nationally using 2002, 2007 and 2012 data from Statistics NZ and DairyNZ.FindingsThe results show positive spatial spillovers for most intensive inputs. The high level of effluent use and estimated negative yield response to nitrogen suggests that an opportunity exists for greater use of effluent as a substitute for nitrogenous fertilizer. Substitution has the potential to reduce dependence on fertilizer and contribute to a reduction in the nutrient pollution.Originality/valueThis paper is the first empirical application of spatial econometric methods to examine the spatial relevance of dairy yields and intensive farming in NZ. In particular, the spatial panel data model accounts for cross-sectional dependence and controls for heterogeneity. The results contribute to an understanding of how farmers can improve their management of intensive inputs and contribute to the formation of regional environmental policy that recognizes regional heterogeneity.

Structure liming enhances aggregate stability and gives varying crop responses on clayey soils

ABSTRACTIt has been suggested that liming can improve soil structure and thereby decrease losses of particles and associated nutrients. In this study, two types of structure lime, slaked lime (Ca(OH)2) and a mixed product of calcium carbonate (CaCO3) and slaked lime (Ca(OH)2), were applied at three different rates in field trials on clayey soils (23%–40% clay). A combination of primary tillage and structure liming was also studied, in a split-plot trial on a clayey soil (25% clay). Aggregate (2–5 mm) stability, measured as reduction in turbidity (which is strongly correlated with losses of particulate phosphorus), was significantly increased with the highest application rates of both structure lime products. Aggregate size distribution was also improved with structure lime, creating a finer tilth in the seedbed. Yield response to structure lime was not consistent, with both negative and positive responses over the four-year study period. Positive yield responses can possibly be attributed to the finer tilth preventing evaporation in two dry growing seasons. Negative yield responses were probably an effect of impaired phosphorus availability associated with limited precipitation in May-July in 2011 and 2013. Two years after liming, soil pH levels were significantly elevated in plots with the highest application rate of structure lime, whereas no significant increases were found three years after liming. However, a lingering effect of liming was still detectable, as manganese concentration in barley grain was significantly lower in plots with the highest application rates of both structure lime products in the fourth study year. These results indicate that structure liming can be used as a measure to mitigate phosphorus losses from clayey soils, thereby preventing eutrophication of nearby waters. However, the yield response was varying and unpredictable and thus further investigations are needed to determine the circumstances in which field liming can act efficiently not only to prevent phosphorus losses, but also to ensure consistent yield increases.

Regional, seasonal, cultivar and crop-year effects on sugarcane responses to residue mulching

Inconsistent agronomic responses of sugarcane (Saccharum spp.) to residue mulching are due to complex interactions between soil, climatic, management and genetic factors. Information on mulch responses of diverse cultivars in contrasting environments, over multiple ratoon crops, in different cropping seasons (winter vs summer) are limited. This study aimed to quantify mulch responses in three diverse environments typical of the South African sugarcane industry and to identify factors causing such responses. Three separate factorial experiments (eight cultivars, burnt or mulched at harvest) were established in the rainfed, irrigated and temperate regions of the industry, harvested over multiple ratoon crops (up to six), with summer and winter crop starts. Mulching was significantly beneficial to cane yields in the rainfed trial (up to 20t/ha improvement in a single crop), marginally beneficial in the irrigated trial, and unfavourable in the cooler temperate trial. The effects of cultivar and season (winter vs summer crop start) were negligible in comparison to regional and crop-year effects. Cultivar sensitivities to mulching were only evident in the temperate trial. A principal components analysis (PCA) biplot separated crops according to their responses to mulching and identified climatic factors responsible for differential responses. Water availability (as represented by a crop model derived drought index) was a primary driver of positive yield responses in the rainfed trial and the differential ratoon responses observed in the irrigated trial. Mulch responses in the irrigated trial were rainfall dependent, ranging from 0 to 20% improvements in water limiting years, to negative responses when water was not limiting. Low temperatures created by the residue layer was identified as a cause of negative yield responses observed in the temperate trial, mainly through delayed canopy development effects. Multivariate methods such as PCA are recommended to identify climatic, soil, genetic and management causes of differential mulch responses in sugarcane, either through analysis of multi-environment experiments or through meta-analysis of available literature.

The interaction between soil pH and phosphorus for wheat yield and the impact of lime-induced changes to soil aluminium and potassium

Interactions between soil pH and phosphorus (P) for plant growth have been widely reported; however, most studies have been based on pasture species, and the agronomic importance of this interaction for acid-tolerant wheat in soils with near-sufficient levels of fertility is unclear. We conducted field experiments with wheat at two sites with acid soils where lime treatments that had been applied in the 6 years preceding the experiments caused significant changes to soil pH, extractable aluminium (Al), soil nutrients and exchangeable cations. Soil pH(CaCl2) at 0–10cm was 4.7 without lime and 6.2 with lime at Merredin, and 4.7 without lime and 6.5 with lime at Wongan Hills. A significant lime×P interaction (P&lt;0.05) for grain yield was observed at both sites. At Merredin, this interaction was negative, i.e. the combined effect of soil pH and P was less than their additive effect; the difference between the dose–response curves without lime and with lime was greatest at 0kgPha–1 and the curves converged at 32kgPha–1. At Wongan Hills, the interaction was positive (combined effect greater than the additive effect), and lime application reduced grain yield. The lime×P interactions observed are agronomically important because different fertiliser P levels were required to maximise grain yield. A lime-induced reduction in Al phytotoxicity was the dominant mechanism for this interaction at Merredin. The negative grain yield response to lime at Wongan Hills was attributed to a combination of marginal soil potassium (K) supply and lime-induced reduction in soil K availability.

Effect of nitrogen fertiliser management on soil mineral nitrogen, nitrous oxide losses, yield and nitrogen uptake of wheat growing in waterlogging-prone soils of south-eastern Australia

Some of the highest nitrous oxide (N2O) emissions arising from Australian agriculture have been recorded in the high-rainfall zone (&gt;650mm) of south-western Victoria. Understanding the association between nitrogen (N) management, crop N uptake and gaseous losses is needed to reduce N2O losses. Field experiments studied the effect of N-fertiliser management on N2O emissions, crop N uptake and crop productivity at Hamilton and Tarrington in south-western Victoria. Management included five rates of urea-N fertiliser (0, 25, 50, 100 and 200kgN/ha) topdressed at either mid-tillering or first-node growth stages of wheat development; urea-N deep-banded 10cm below the seed at sowing; and urea coated with the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) was either topdressed or deep-banded. Pre-sowing soil profile chemical properties were determined before static chambers were installed to measure N2O losses, accompanied by wheat dry matter, crop N uptake and grain yield and quality, to measure treatment differences. N2O losses increased significantly (P≤0.10) where urea-N was deep-banded, resulting in a 2–2.5-fold increase in losses, compared with the nil N control. The high N2O losses from deep-banding N appeared to result from winter waterlogging triggering gaseous or drainage losses before wheat reached peak growth and demand for N in spring. Despite the high losses from deep-banding urea-N, grain yields were largely unaffected by N management, except at Hamilton in 2012, where topdressed wheat growing in a soil with large reserves of NO3–-N, and later experiencing post-anthesis water deficit resulted in a negative grain yield response. All sites had high concentrations of soil organic carbon (&gt;2.8%) and the potential for large amounts of N mineralisation throughout the growing season to supplement low N fertiliser recovery. However, topdressed urea-N resulted in significant enrichment of crop tissue (P≤0.004) and associated positive response in grain protein compared with the deep banded and nil N treatments. 3,4-Dimethylpyrazole phosphate (DMPP)-coated urea provided no additional benefit to crop yield over conventional urea N. Our study highlighted the importance of synchronising N supply with peak crop N demand to encourage greater synthetic N uptake and mitigation of N2O losses.

The critical role of extreme heat for maize production in the United States

Statistical studies of rainfed maize yields in the United States(1) and elsewhere(2) have indicated two clear features: a strong negative yield response to accumulation of temperatures above 30 degrees C (or extreme degree days (EDD)), and a relatively weak response to seasonal rainfall. Here we show that the process-based Agricultural Production Systems Simulator (APSIM) is able to reproduce both of these relationships in the Midwestern United States and provide insight into underlying mechanisms. The predominant effects of EDD in APSIM are associated with increased vapour pressure deficit, which contributes to water stress in two ways: by increasing demand for soil water to sustain a given rate of carbon assimilation, and by reducing future supply of soil water by raising transpiration rates. APSIM computes daily water stress as the ratio of water supply to demand, and during the critical month of July this ratio is three times more responsive to 2 degrees C warming than to a 20% precipitation reduction. The results suggest a relatively minor role for direct heat stress on reproductive organs at present temperatures in this region. Effects of elevated CO2 on transpiration efficiency should reduce yield sensitivity to EDD in the coming decades, but at most by 25%.

Identifying Factors Controlling the Continuous Corn Yield Penalty

It is widely accepted that yields decline when corn (Zea mays L.) is grown continuously vs. in rotation with soybean [Glycine max (L.) Merr.], although causes for the yield reduction are unclear. The primary objective of this study was to elucidate the source(s) of the continuous corn yield penalty (CCYP). The experiment was conducted from 2005 to 2010 in east‐central Illinois beginning with third‐year continuous corn (CC) or a soybean–corn (SC) rotation at six N fertilizer rates. Averaged across all years, yield at the agronomic optimum N rate for CC was 8.84 Mg ha−1 and for SC was 10.20 Mg ha−1, resulting in a CCYP of 1.36 Mg ha−1; values ranged yearly from 0.47 to 2.23 Mg ha−1. Using a regression model, three significant and independent predictors explained &gt;99% of the variability in the CCYP: unfertilized CC yield (0NCCYD), years in CC (CCYRS), and the difference between CC and SC delta yields (maximum yield – unfertilized yield) (DELTADIFF). The strongest predictor, 0NCCYD, reflects net soil N mineralization and demonstrates that it decreases in CC systems. The CCYRS was strongly and positively correlated with CCYP, indicating that the CCYP increased through Year 7. We believe that CCYRS measures the effects of accumulated corn residue in CC systems. Finally, we consider DELTADIFF to be a measure of the interaction between yearly weather patterns and crop rotation, which results in more negative yield responses for CC than SC under hot or dry conditions. This study concluded that the primary causative agents of the CCYP are N availability, corn residue accumulation, and weather.

Impacts of observed growing-season warming trends since 1980 on crop yields in China

This study explores the effects of observed warming trends since 1980 on crop yields at both national and regional scales for the four main staple crops (rice, wheat, maize, and soybean) in China, using gridded climate and observed crop yield data, and identifies the areas in China where food production is susceptible to warming. National scale yield–temperature relationships show that there are clear negative yield responses of maize, wheat, and soybean to increased growing-season temperature. Regional scale yield–temperature relationships show that over 50 % of the arable land exhibited yield susceptibility to past warming trends, with maize showing the highest vulnerability and rice the lowest vulnerability. However, in most of the main food-producing areas, crops experienced increases or insignificant changes in yields due to better agronomic management. The Loess plain is revealed as the most vulnerable region to the past warming, as at least two food crops have exhibited the signs of warming susceptibility in the majority of the area. We also find considerable yield reductions in spring wheat in the central northeast, winter wheat in the Yellow River basin, and maize in Southwest China. These findings of hotspot areas are valuable in prioritizing future climate adaptation strategies for Chinese agriculture.