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UK grasslands perform important environmental and economic functions, but their future productivity under climate change is uncertain. Spring hay yields from 1902 to 2016 at one site (the Park Grass Long Term Experiment) in southern England under four different fertilizer regimes were modelled in response to weather (seasonal temperature and rainfall). The modelling approach applied comprised: (1) a Bayesian model comparison to model parametrically the heteroskedasticity in a gamma likelihood function; (2) a Bayesian varying intercept multiple regression model with an autoregressive lag one process (to incorporate the effect of productivity in the previous year) of the response of hay yield to weather from 1902 to 2016. The model confirmed that warmer and drier years, specifically, autumn, winter and spring, in the twentieth and twenty-first centuries reduced yield. The model was applied to forecast future spring hay yields at Park Grass under different climate change scenarios (HadGEM2 and GISS RCP 4.5 and 8.5). This application indicated that yields are forecast to decline further between 2020 and 2080, by as much as 48-50%. These projections are specific to Park Grass, but implied a severe reduction in grassland productivity in southern England with climate change during the twenty-first century.

Clearing natural vegetation to establish arable agriculture (cropland) almost invariably causes a loss of soil organic carbon (SOC). Is it possible to restore soil that continues in arable agriculture to the pre-clearance SOC level through modified management practices? To address this question we reviewed evidence from long-term experiments at Rothamsted Research, UK, Bad Lauchstädt, Germany, Sanborn Field, USA and Brazil and both experiments and surveys of farmers' fields in Ethiopia, Australia, Zimbabwe, UK and Chile. In most cases SOC content in soil under arable cropping was in the range 38–67% of pre-clearance values. Returning crop residues, adding manures or including periods of pasture within arable rotations increased this, often to 60–70% of initial values. Under tropical climatic conditions SOC loss after clearance was particularly rapid, e.g. a loss of >50% in less than 10 years in smallholder farmers' fields in Zimbabwe. If larger yielding crops were grown, using fertilizers, and maize stover returned instead of being grazed by cattle, the loss was reduced. An important exception to the general trend of SOC loss after clearance was clearing Cerrado vegetation on highly weathered acidic soils in Brazil and conversion to cropping with maize and soybean. Other exceptions were unrealistically large annual applications of manure and including long periods of pasture in a highly SOC-retentive volcanic soil. Also, introducing irrigated agriculture in a low rainfall region can increase SOC beyond the natural value due to increased plant biomass production. For reasons of sustainability and soil health it is important to maintain SOC as high as practically possible in arable soils, but we conclude that in the vast majority of situations it is unrealistic to expect to maintain pre-clearance values. To maintain global SOC stocks at we consider it is more important to reduce current rates of land clearance and sustainably produce necessary food on existing agricultural land. [ABSTRACT FROM AUTHOR]

Our study tests the emerging paradigm that biochemical recalcitrance does not affect substantially long-term (50 years) SOC persistence. We analyzed the molecular composition of SOC in archived soils originating from four European long-term bare fallow experiments (Askov, Rothamsted, Versailles and Ultuna). The soils had been collected after various periods (up to 53 years) under bare fallow. With increasing duration of bare fallow without new organic inputs, the relative abundance of cutin- and suberin-derived compounds declined substantially, and the abundance of lignin-derived compounds was close to zero. Conversely, the relative abundance of plant-derived long-chain alkanes remained almost constant or increased during the bare fallow period. The relative abundance of N-containing compounds, considered to be abundant in SOC derived from microbial activity, increased consistently illustrating that microbial turnover of SOC continues even when plant inputs are stopped. The persistence of the different families of plant-derived compounds differed markedly over the scale of half a century, which may be ascribed to their contrasting chemical characteristics and recalcitrance, or to differences in their interactions with the soil mineral matrix, and likely some combination since chemical composition drives the degree of mineral association. Using soil from this unique set of long-term bare fallow experiments, we provide direct evidence that multi-decadal scale persistent SOC is enriched in microbe-derived compounds but also includes a substantial fraction of plant-derived compounds. [ABSTRACT FROM AUTHOR]

Under the increase in atmospheric CO2 during the last century, variable increases in the intrinsic water-use efficiency ( Wi), i.e., the ratio between carbon assimilation rate ( A) and stomatal conductance ( gs), of C3 vegetation have been observed. Here, we ask if long-term nutrient status and especially nitrogen supply have an effect on the CO2 response of Wi in a temperate seminatural C3 grassland. This analysis draws on the long-term trends (1915-2009) in Wi, derived from carbon isotope analysis, of archived hay and herbage from the Park Grass Experiment at Rothamsted ( South- East England). Plant samples came from five fertilizer treatments, each with different annual nitrogen (N; 0, 48 or 96 kg ha−1), phosphorus (P; 0 or 35 kg ha−1) and potassium (K; 0 or 225 kg ha−1) applications, with lime as required to maintain soil pH near 7. Carbon isotope discrimination (13Δ) increased significantly ( P < 0.001) on the Control (0.9‰ per 100 ppm CO2 increase). This trend differed significantly ( P < 0.01) from those observed on the fertilized treatments ( PK only: 0.4‰ per 100 ppm CO2 increase, P < 0.001; Low N only, Low N+PK, High N+PK: no significant increase). The 13Δ trends on fertilized treatments did not differ significantly from each other. However, N status, assessed as N fertilizer supply plus an estimate of biologically fixed N, was negatively related ( r2 = 0.88; P < 0.02) to the trend for 13Δ against CO2. Other indices of N status exhibited similar relationships. Accordingly, the increase in Wi at High N+PK was twice that of the Control (+28% resp. +13% relative to 1915). In addition, the CO2 responsiveness of 13Δ was related to the grass content of the plant community. This may have been due to the greater CO2 responsiveness of gs in grasses relative to forbs. Thus, the greater CO2 response of grass-rich fertilized swards may be related to effects of nutrient supply on botanical composition. [ABSTRACT FROM AUTHOR]

• Climate change is about more than just increasing temperature. • Multivariate analysis (PCA, K -means) shows changes in annual weather patterns. • Ten distinct clusters for annual weather patterns over 125 years at one UK site. • The dominant cluster since 1991 has higher temperatures and more intense rainfall. • Crop yields (biomass: wheat, barley, grass) vary considerably with weather cluster. The long-term increasing trend of annual mean temperature is only one aspect of recent climate change. Other changes in climate, seen in within-year weather patterns relevant to crop production, have also occurred since the late-19th Century. Multivariate analysis combining Principal Components Analysis and K-means clustering applied to temporal meteorological datasets (monthly summaries of rainfall, temperature and sunlight duration at Rothamsted Research, UK, between 1892 and 2016) identified ten distinct clusters of years, each with different annual weather patterns. The frequency of occurrence of the years within each cluster altered considerably during this period, with the late 20th and early 21st Century distinctly different to earlier in the 20th Century, providing clear evidence of climate change with regard to the whole weather profile rather than just warming alone. The most-frequently represented cluster of the 21st Century to date had warmer temperatures with more intense rainfall but a dry June, compared to all other clusters. Half of the clusters identified were not represented in the most-recent 25-year period. Analysis of the total biomass yield of winter wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), and grassland amongst the different weather clusters showed that years in clusters typical of the 20th Century climate provided greater off-take than those from the early-21st Century, but this impact was less for the pasture than for the two cereal crops implying herbage production was the more resilient to the changing climate at this site. [ABSTRACT FROM AUTHOR]

• Higher crop diversity and organic matter inputs increased yield stability. • Moderate N fertilization (70 kg N ha−1) benefitted yield stability. • Organic matter improved environmental adaptability of barley in cereal rotations. • Production risk was lower with higher crop diversity and organic matter inputs. In the face of climate change, the potential impacts of adverse weather conditions on the productivity and vulnerability of cropping systems (CS) worldwide constitute a key agronomic issue upon which global food security depends. To date, little information regarding how the diversity of CS or agricultural practices affect the long-term yield responses of winter barley is available. The aim of this study was to investigate the impact of CS diversity in terms of cropping sequences, organic matter supplies, and nitrogen (N) fertilization on the yield vulnerability of winter barley. Yields were evaluated in terms of their stability, environmental adaptability, and production risk (probability of yield loss). Data from a 27-year experiment were statistically analyzed using three mixed models giving residual maximum likelihood estimates including the Shukla stability variance index, the Finlay-Wilkinson environmental regression, and the Eskridge risk assessment approach. The results showed that winter barley grown in cropping sequences dominated by cereals had lower yield stability and environmental adaptability and greater production risks compared with winter barley grown in CS with higher crop diversity and additional organic matter inputs. When barley yields were compared at three doses of mineral N, the highest yield stability was achieved with the medium N dose (70 kg N ha−1), followed by the higher level of N (140 kg N ha−1). The most unstable yields with the highest production risks were observed when barley was grown without any mineral N fertilization. Overall, a higher level of crop diversity with organic matter inputs and intermediate N fertilization resulted in lower yield vulnerability in winter barley. [ABSTRACT FROM AUTHOR]

• Variation in yield-nitrogen responses explored using long-term experiments (LTEs). • Yield-nitrogen relationship modelled using linear-plus-exponential function. • Inter-annual variation in parameters explained using monthly weather summaries. • Modelling allows separation of effects of environmental and agronomic factors. • Selected monthly weather variables associated with key crop development processes. The effect of weather on inter-annual variation in the crop yield response to nitrogen (N) fertilizer for winter wheat (Triticum aestivvum L.) and spring barley (Hordeum vulgare L.) was investigated using yield data from the Broadbalk Wheat and Hoosfield Spring Barley long-term experiments at Rothamsted Research. Grain yields of crops from 1968 to 2016 were modelled as a function of N rates using a linear-plus-exponential (LEXP) function. The extent to which inter-annual variation in the parameters of these responses was explained by variations in weather (monthly summarized temperatures and rainfall), and by changes in the cultivar grown, was assessed. The inter-annual variability in rainfall and underlying temperature influenced the crop N response and hence grain yields in both crops. Asymptotic yields in wheat were particularly sensitive to mean temperature in November, April and May, and to total rainfall in October, February and June. In spring barley asymptotic yields were sensitive to mean temperature in February and June, and to total rainfall in April to July inclusive and September. The method presented here explores the separation of agronomic and environmental (weather) influences on crop yield over time. Fitting N response curves across multiple treatments can support an informative analysis of the influence of weather variation on the yield variability. Whilst there are issues of the confounding and collinearity of explanatory variables within such models, and that other factors also influence yields over time, our study confirms the considerable impact of weather variables at certain times of the year. This emphasizes the importance of including weather temporal variation when evaluating the impacts of climate change on crops. [ABSTRACT FROM AUTHOR]