In recent decades farmers in high-income countries and China and India have built up a large reserve of residual soil P in cropland. This reserve can now be used by crops, and in high-income ...countries the use of mineral P fertilizer has recently been decreasing with even negative soil P budgets in Europe. In contrast to P, much of N surpluses are emitted to the environment via air and water and large quantities of N are transported in aquifers with long travel times (decades and longer). N fertilizer use in high-income countries has not been decreasing in recent years; increasing N use efficiency and utilization of accumulated residual soil P allowed continued increases in crop yields. However, there are ecological risks associated with the legacy of excessive nutrient mobilization in the 1970s and 1980s. Landscapes have a memory for N and P; N concentrations in many rivers do not respond to increased agricultural N use efficiency, and European water quality is threatened by rapidly increasing N:P ratios. Developing countries can avoid such problems by integrated management of N, P and other nutrients accounting for residual soil P, while avoiding legacies associated with the type of past or continuing mismanagement of high-income countries, China and India.
In the last decade the multifunctional agriculture (MFA) concept has emerged as a key notion in scientific and policy debates on the future of agriculture and rural development. Broadly speaking, MFA ...refers to the fact that agricultural activity beyond its role of producing food and fibre may also have several other functions such as renewable natural resources management, landscape and biodiversity conservation and contribution to the socio-economic viability of rural areas. The use of the concept can be traced to a number of wider societal and political transformation processes, which have influenced scientific and policy approaches in different ways amongst countries and disciplines. This paper critically discusses various existing research approaches to MFA, both from natural and social sciences. To this aim different strands of literature are classified according to their focus on specific governance mechanisms and levels of analysis into four main categories of research approaches (market regulation, land-use approaches, actor-oriented and public regulation approaches). For each category an overview of the state-of-the-art of research is given and an assessment is made of its strengths and weaknesses. The review demonstrates that the multifunctionality concept has attracted a wealth of scientific contributions, which have considerably improved our understanding of key aspects of MFA. At the same time approaches in the four categories have remained fragmented and each has limitations to understand MFA in all its complexity due to inherent constraints of applied conceptualizations and associated disciplinary backgrounds. To go beyond these limitations, we contend, new meta-level frameworks of analysis are to be developed that enable a more integrated approach. The paper concludes by presenting the main lines of an integrative, transitional framework for the study of MFA, which analyses multifunctional agriculture against the background of wider societal change processes towards sustainability and identifies a number of key elements and research challenges for this.
Ethiopia is one of the countries most vulnerable to the impacts of climate variability and change on agriculture. The present study aims to understand and characterize agro-climatic variability and ...changes and associated risks with respect to implications for rainfed crop production in the Central Rift Valley (CRV). Temporal variability and extreme values of selected rainfall and temperature indices were analysed and trends were evaluated using Sen's slope estimator and Mann–Kendall trend test methods. Projected future changes in rainfall and temperature for the 2080s relative to the 1971–90 baseline period were determined based on four General Circulation Models (GCMs) and two emission scenarios (SRES, A2 and B1). The analysis for current climate showed that in the short rainy season (March–May), total mean rainfall varies spatially from 178 to 358 mm with a coefficient of variation (CV) of 32–50%. In the main (long) rainy season (June–September), total mean rainfall ranges between 420 and 680 mm with a CV of 15–40%. During the period 1977–2007, total rainfall decreased but not significantly. Also, there was a decrease in the number of rainy days associated with an increase (statistically not significant) in the intensity per rainfall event for the main rainy season, which can have implications for soil and nutrient losses through erosion and run-off. The reduced number of rainy days increased the length of intermediate dry spells by 0·8 days per decade, leading to crop moisture stress during the growing season. There was also a large inter-annual variability in the length of growing season, ranging from 76 to 239 days. The mean annual temperature exhibited a significant warming trend of 0·12–0·54 °C per decade. Projections from GCMs suggest that future annual rainfall will change by +10 to −40% by 2080. Rainfall will increase during November–December (outside the growing season), but will decline during the growing seasons. Also, the length of the growing season is expected to be reduced by 12–35%. The annual mean temperature is expected to increase in the range of 1·4–4·1 °C by 2080. The past and future climate trends, especially in terms of rainfall and its variability, pose major risks to rainfed agriculture. Specific adaptation strategies are needed for the CRV to cope with the risks, sustain farming and improve food security.
Grasslands provide grass and fodder to sustain the growing need for ruminant meat and milk. Soil nutrients in grasslands are removed through withdrawal in these livestock products and through animal ...manure that originates from grasslands and is spread in croplands. This leads to loss of soil fertility, because globally most grasslands receive no mineral fertilizer. Here we show that phosphorus (P) inputs (mineral and organic) in global grasslands will have to increase more than fourfold in 2050 relative to 2005 to achieve an anticipated 80% increase in grass production (for milk and meat), while maintaining the soil P status. Combined with requirements for cropland, we estimate that mineral P fertilizer use must double by 2050 to sustain future crop and grassland production. Our findings point to the need to better understand the role of grasslands and their soil P status and their importance for global food security.
Bangladesh faces huge challenges in achieving food security due to its high population, diet changes, and limited room for expanding cropland and cropping intensity. The objective of this study is to ...assess the degree to which Bangladesh can be self-sufficient in terms of domestic maize, rice and wheat production by the years 2030 and 2050 by closing the existing gap (Yg) between yield potential (Yp) and actual farm yield (Ya), accounting for possible changes in cropland area. Yield potential and yield gaps were calculated for the three crops using well-validated crop models and site-specific weather, management and soil data, and upscaled to the whole country. We assessed potential grain production in the years 2030 and 2050 for six land use change scenarios (general decrease in arable land; declining ground water tables in the north; cropping of fallow areas in the south; effect of sea level rise; increased cropping intensity; and larger share of cash crops) and three levels of Yg closure (1: no yield increase; 2: Yg closure at a level equivalent to 50% (50% Yg closure); 3: Yg closure to a level of 85% of Yp (irrigated crops) and 80% of water-limited yield potential or Yw (rainfed crops) (full Yg closure)). In addition, changes in demand with low and high population growth rates, and substitution of rice by maize in future diets were also examined. Total aggregated demand of the three cereals (in milled rice equivalents) in 2030 and 2050, based on the UN median population variant, is projected to be 21 and 24% higher than in 2010. Current Yg represent 50% (irrigated rice), 48–63% (rainfed rice), 49% (irrigated wheat), 40% (rainfed wheat), 46% (irrigated maize), and 44% (rainfed maize) of their Yp or Yw. With 50% Yg closure and for various land use changes, self-sufficiency ratio will be >1 for rice in 2030 and about one in 2050 but well below one for maize and wheat in both 2030 and 2050. With full Yg closure, self-sufficiency ratios will be well above one for rice and all three cereals jointly but below one for maize and wheat for all scenarios, except for the scenario with drastic decrease in boro rice area to allow for area expansion for cash crops. Full Yg closure of all cereals is needed to compensate for area decreases and demand increases, and then even some maize and large amounts of wheat imports will be required to satisfy demand in future. The results of this analysis have important implications for Bangladesh and other countries with high population growth rate, shrinking arable land due to rapid urbanization, and highly vulnerable to climate change.
•Relative yield gap (Yg) across water regime is around 45% (maize and wheat) and 50-60% (rice) in Bangladesh.•Relative Yg of three cereals is about 46-50% (under irrigation) and 40-63% (under rainfed).•With 50% Yg closure, self-sufficiency ratio (SSR) in 2050 will be ~ 1 (rice) but significantly<1 (maize and wheat).•With full Yg closure, SSR in 2050 will be greater than 1 (rice) but less than 1 (maize and wheat).•Full Yg closure in future can compensate area decrease in rice but some maize and large wheat imports will be inevitable.
The complexity of risks posed by climate change and possible adaptations for crop production has called for integrated assessment and modelling (IAM) approaches linking biophysical and economic ...models. This paper attempts to provide an overview of the present state of crop modelling to assess climate change risks to food production and to which extent crop models comply with IAM demands. Considerable progress has been made in modelling effects of climate variables, where crop models best satisfy IAM demands. Demands are partly satisfied for simulating commonly required assessment variables. However, progress on the number of simulated crops, uncertainty propagation related to model parameters and structure, adaptations and scaling are less advanced and lagging behind IAM demands. The limitations are considered substantial and apply to a different extent to all crop models. Overcoming these limitations will require joint efforts, and consideration of novel modelling approaches.
•Extreme events and future climate uncertainty represent risk for food production.•Crop models are largely able to simulate crop response to climate factors.•Adaptations are best evaluated in integrated assessment models (IAM).•Key limitations for crop models in IAM are low data availability and integration.•Cross-scale nature of IAM suggests novel modelling approaches are needed.
Background and aims Organic inputs have a positive effect on the soil organic matter balance. They are therefore an important asset for soil fertility and crop growth. This study quantifies the ...additional yield effect due to organic inputs for arable crops in Europe when macronutrients are not a limiting factor. Methods A meta-analysis was performed using data from 20 long-term experiments in Europe. Maxima of yield response curves to nitrogen were compared, with and without organic inputs, under abundant P and K supply. Results We were surprised to find that, across all experiments, the mean additional yield effect of organic inputs was not significant (+ 1.4 % ± 1.6 (95 % confidence interval)). In specific cases however, especially for root and tuber crops, spring sown cereals, or for very sandy soils or wet climates, organic inputs did increase attainable yields. A significant correlation was found between increase in attainable yields and increase in soil organic matter content. Conclusions Aggregating data from 20 long-term experiments in Europe, this study shows that organic inputs and/or soil organic matter do not necessarily increase yields, given sufficient nutrients are supplied by mineral fertilisers. Results show the relevance of some environmental factors for additional yield effect of organic inputs, but no simple relation between organic inputs and crop growth.
Growing global demand for food leads to increased pressure on phosphorus (P), a finite and dwindling resource. China is the largest producer and consumer of P fertilizer in the world. A mass balance ...analysis of historical P use on China's arable land shows that P input substantially exceeds crop P uptake leading to the accumulation of residual soil P. A Dynamic P Pool Simulator (DPPS) model is applied to estimate future P demand in China's arable land. Our simulations show that more sustainable use of P accounting for the residual P can save ca. 20% of the P fertilizer needed until 2050 in China relative to the Rio + 20 Trend scenario. This saving would be equivalent to half of the P required in Africa or sufficient for Western Europe to achieve target crop P uptake in 2050.
•We used multi-model crop growth simulation approach to characterize climate-induced variability and yield gaps of maize.•Maize yield shows high inter-annual variability and this variability is ...explained mainly by the variation in growing season rainfall.•Average farmers’ yields are only 28–30% of simulated water-limited yield.•Improved crop management and climate-proof strategies are needed to sustain production, increase yield and bridge existing yield gaps.•The use of more than one model provides some insight in uncertainty of simulating crop–climate interactions.
There is a high demand for quantitative information on impacts of climate on crop yields, yield gaps and their variability in Ethiopia, yet, quantitative studies that include an indication of uncertainties in the estimates are rare. A multi-model crop growth simulation approach using the two crop models, i.e. Decision Support System for Agro-Technology (DSSAT) and WOrld FOod STudies (WOFOST) was applied to characterize climate-induced variability and yield gaps of maize. The models were calibrated and evaluated with experimental data from the Central Rift Valley (CRV) in Ethiopia. Subsequently, a simulation experiment was carried out with an early maturing (Melkassa1) and a late maturing (BH540) cultivar using historical weather data (1984–2009) of three locations in the CRV. Yield gaps were computed as differences among simulated water-limited yield, on-farm trial yields and average actual farmers’ yields.
The simulation experiment revealed that the potential yield (average across three sites and 1984–2009) is 8.2–9.2 and 6.8–7.1Mg/ha for the late maturing and early maturing cultivars, respectively; ranges indicate mean differences between the two models. The simulated water-limited yield (averaged across three sites and 1984–2009) is 7.2–7.9Mg/ha for the late maturing and 6.1–6.7Mg/ha for the early maturing cultivar. The water-limited yield shows high inter-annual variability (CV 36%) and about 60% of this variability in yield is explained by the variation in growing season rainfall. The gap between average farmers yield and simulated water-limited yield ranges from 4.7 to 6.0Mg/ha. The average farmers’ yields were 2.0–2.3Mg/ha, which is about 1.1–3.1Mg/ha lower than on-farm trial yields. In relative terms, average farmers’ yields are 28–30% of the water-limited yield and 44–65% of on-farm trial yields. Analysis of yield gaps for different number of years to drive average yields indicates that yield gap estimation on the basis of few years may result in misleading conclusions. Approximately ten years of data are required to be able to estimate yield gaps for the Central Rift Valley in a robust manner.
Existing yield gaps indicate that there is scope for significantly increasing maize yield in the CRV and other, similar agro-ecological zones in Africa, through improved crop and climate risk management strategies. As crop models differ in detail of describing the complex, dynamic processes of crop growth, water use and soil water balances, the multi-model approach provides information on the uncertainty in simulating crop–climate interactions.
High extraction of phosphate reserves and low phosphorus utilization efficiency in the food chain in China result in large P losses and serious environmental pollution. The P fertilizer industry, ...soil P surplus, livestock manure P and wastewater P recycling have been identified as the priority sectors based on summarizing several systemic and in-depth reviews of P flows analysis. Mineral P fertilizer production has reached 7.4 Mt P in 2012, which is more than seven times the value in 1980. The large P surpluses in arable land resulted in soil P accumulation of up to 64 Mt during the period 1951–2010. Livestock numbers have increased dramatically (more than ten times) during the period 1949–2012 in China, especially pigs and poultry, and so has the quantity of manure that they produce. The average loading of manure P on arable land in China has increased significantly from 9.5 kg P ha⁻¹ in 1980 to 20.4 kg P ha⁻¹ in 2010. Up to 0.49 Mt of wastewater P discharged without treatment also exerted great pressure on the environment in 2012. Based on an understanding of P interactions in these key sectors, an integrated set of policy options and technical measures is proposed. Taking P flows in China in 2010 as an example, if all of the strategies recommended in this study are adopted in P management, about 4.3, 2.5, 1.6 and 0.3 Mt of P resources, respectively, will be saved in the P fertilizer industry, arable land production, livestock manure and wastewater sectors.
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