Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Hoe is onze wereld duurzaam te voeden?
Ittersum, Martin van - \ 2018
Meeting the dual demand for animal products and climate change mitigation by narrowing yield gaps
Linden, A. van der; Gerber, P.J. ; Ven, G.W.J. van de; Ittersum, M.K. van; Boer, I.J.M. de; Oosting, S.J. - \ 2018
In: Book of abstracts of the 69th Annual Meeting of the European Federation of Animal Science. - Wageningen : Wageningen Academic Publishers (Book of abstracts 24) - ISBN 9789086863235 - p. 340 - 340.
Exploring options to recycle and prevent phosphorus waste in a food system
Kernebeek, H.R.J. van; Oosting, S.J. ; Ittersum, M.K. van; Ripoll Bosch, R. ; Boer, I.J.M. de - \ 2018
In: Book of abstracts of the 69th Annual Meeting of the European Federation of Animal Science. - Wageningen : Wageningen Academic Publishers (Book of abstracts 24) - ISBN 9789086863235 - p. 420 - 420.
Sustainable development goal 2: Improved targets and indicators for agriculture and food security
Gil, Juliana Dias Bernardes ; Reidsma, Pytrik ; Giller, Ken ; Todman, Lindsay ; Whitmore, Andrew ; Ittersum, Martin van - \ 2018
Ambio (2018). - ISSN 0044-7447 - 14 p.
The pursuit of global food security and agricultural sustainability, the dual aim of the second sustainable development goal (SDG-2), requires urgent and concerted action from developing and developed countries. This, in turn, depends on clear and universally applicable targets and indicators which are partially lacking. The novel and complex nature of the SDGs poses further challenges to their implementation on the ground, especially in the face of interlinkages across SDG objectives and scales. Here we review the existing SDG-2 indicators, propose improvements to facilitate their operationalization, and illustrate their practical implementation in Nigeria, Brazil and the Netherlands. This exercise provides insights into the concrete actions needed to achieve SDG-2 across contrasting development contexts and highlights the challenges of addressing the links between targets and indicators within and beyond SDG-2. Ultimately, it underscores the need for integrated policies and reveals opportunities to leverage the fulfillment of SDG-2 worldwide.
Prospect for increasing grain legume crop production in East Africa
Loon, Marloes P. van; Deng, Nanyan ; Grassini, Patricio ; Rattalino Edreira, Juan I. ; Wolde-meskel, Endalkachew ; Baijukya, Frederick ; Marrou, Hélène ; Ittersum, Martin K. van - \ 2018
European Journal of Agronomy 101 (2018). - ISSN 1161-0301 - p. 140 - 148.
Chickpea - Common bean - Cowpea - Food self-sufficiency - Groundnut - Legumes - Pigeonpea - Sub-Saharan Africa - Yield gap - Yield potential

Agricultural production in East Africa (E-Afr) has to increase drastically to meet future food demand. Yield gap assessment provides important information on the degree to which production can be increased on existing cropland. Most research on yield gap analysis has focussed on cereal crops, while legumes have received less attention despite of their relatively large area, and their importance as source of protein in smallholder farming systems in E-Afr. The objectives of this study were to (i) estimate water-limited yield potential (Yw) and yield gaps (Yg) for major grain legume crops in E-Afr, and (ii) estimate how narrowing the current legume Yg can contribute to food self-sufficiency by the year 2050. We focussed on Ethiopia, Kenya, and Tanzania, and five legumes crops including chickpea, common bean, cowpea, groundnut, and pigeonpea. A bottom-up approach which entails that local weather, soil and agronomic data was used as input for crop modelling (SSM-legumes) in a spatial framework, to estimate Yw, actual on-farm yield (Ya), and Yg from local to regional scale. Future legume self-sufficiency was assessed for 2050 demand assuming different Yg closure scenarios. On average, Ya was 25% of Yw across all legume-county combinations, being 15% for Kenya, 23% for Tanzania and 41% for Ethiopia. On average, common bean had the largest Yg of 2.6 Mg ha−1and chickpea the smallest (1.4 Mg ha−1). Closure of the exploitable Yg (i.e., 80% of Yw) can help to meet future legume demand in both Kenya and Tanzania, while it seems not to be sufficient in Ethiopia.

Integrated Assessment of the EU’s Greening Reform and Feed Self-Sufficiency Scenarios on Dairy Farms in Piemonte, Italy
Gaudino, Stefano ; Reidsma, Pytrik ; Kanellopoulos, Argyris ; Sacco, Dario ; Ittersum, Martin Van - \ 2018
Agriculture 8 (2018)9. - ISSN 2077-0472
Specialised dairy farms are challenged to be competitive and yet respect environmental constrains. A tighter integration of cropping and livestock systems, both in terms of feed and manure flows, can be beneficial for the farm economy and the environment. The greening of the direct payments, which was introduced in the European Union’s greening reform in 2013, is assumed to
stimulate the transition towards more sustainable systems. The aim of this study was to quantitatively assess the impacts of greening policies on important economic and environmental indicators of sustainability, and explore potential further improvements in policies. The Farm System SIMulator (FSSIM) bioeconomic farm model was used to simulate the consequences of scenarios of policy change on three representative dairy farms in Piedmont, Italy, i.e., an ‘intensive’, an ‘extensive’, and an ‘organic’ dairy farm. Results showed that in general, there is a large potential to increase the current economic performance of all of the farms. The most profitable activity is milk production, resulting in the allocation of all of the available farm land to feed production. Imposing feed self-sufficiency targets results in a larger adaptation of current managerial practice than the adaptations that are required due to the greening policy scenario. It was shown that the cropping system is not always able to sustain the
actual herd composition when 90% feed self-sufficiency is imposed. Regarding the greening policies, it is shown that extensive and organic farms already largely comply with the greening constrains, and the extra subsidy is therefore a bonus, while the intensive farm is likely to sacrifice the subsidy, as adapting the farm plan will substantially reduce profit. The introduction of nitrogen (N)-fixing
crops in ecological focus areas was the easiest greening strategy to adopt, and led to an increase in the protein feed self-sufficiency. In conclusion, it is important to note that the greening policy in its current form does not lead to reduced environmental impacts. This implies that in order to improve
environmental performance, regulations are needed rather than voluntary economic incentives.
Multimodel ensembles improve predictions of crop–environment–management interactions
Wallach, Daniel ; Martre, Pierre ; Liu, Bing ; Asseng, Senthold ; Ewert, Frank ; Thorburn, Peter J. ; Ittersum, Martin van; Aggarwal, Pramod K. ; Ahmed, Mukhtar ; Basso, Bruno ; Biernath, Christian ; Cammarano, Davide ; Challinor, Andrew J. ; Sanctis, Giacomo De; Dumont, Benjamin ; Eyshi Rezaei, Ehsan ; Fereres, Elias ; Fitzgerald, Glenn J. ; Gao, Y. ; Garcia-Vila, Margarita ; Gayler, Sebastian ; Girousse, Christine ; Hoogenboom, Gerrit ; Horan, Heidi ; Izaurralde, Roberto C. ; Jones, Curtis D. ; Kassie, Belay T. ; Kersebaum, Christian C. ; Klein, Christian ; Koehler, Ann Kristin ; Maiorano, Andrea ; Minoli, Sara ; Müller, Christoph ; Naresh Kumar, Soora ; Nendel, Claas ; O'Leary, Garry J. ; Palosuo, Taru ; Priesack, Eckart ; Ripoche, Dominique ; Rötter, Reimund P. ; Semenov, Mikhail A. ; Stöckle, Claudio ; Stratonovitch, Pierre ; Streck, Thilo ; Supit, Iwan ; Tao, Fulu ; Wolf, Joost ; Zhang, Zhao - \ 2018
Global Change Biology (2018). - ISSN 1354-1013
climate change impact - crop models - ensemble mean - ensemble median - multimodel ensemble - prediction

A recent innovation in assessment of climate change impact on agricultural production has been to use crop multimodel ensembles (MMEs). These studies usually find large variability between individual models but that the ensemble mean (e-mean) and median (e-median) often seem to predict quite well. However, few studies have specifically been concerned with the predictive quality of those ensemble predictors. We ask what is the predictive quality of e-mean and e-median, and how does that depend on the ensemble characteristics. Our empirical results are based on five MME studies applied to wheat, using different data sets but the same 25 crop models. We show that the ensemble predictors have quite high skill and are better than most and sometimes all individual models for most groups of environments and most response variables. Mean squared error of e-mean decreases monotonically with the size of the ensemble if models are added at random, but has a minimum at usually 2–6 models if best-fit models are added first. Our theoretical results describe the ensemble using four parameters: average bias, model effect variance, environment effect variance, and interaction variance. We show analytically that mean squared error of prediction (MSEP) of e-mean will always be smaller than MSEP averaged over models and will be less than MSEP of the best model if squared bias is less than the interaction variance. If models are added to the ensemble at random, MSEP of e-mean will decrease as the inverse of ensemble size, with a minimum equal to squared bias plus interaction variance. This minimum value is not necessarily small, and so it is important to evaluate the predictive quality of e-mean for each target population of environments. These results provide new information on the advantages of ensemble predictors, but also show their limitations.

Can potato add to China's food self-sufficiency? The scope for increasing potato production in China
Wang, N. ; Reidsma, P. ; Pronk, A.A. ; Wit, A.J.W. de; Ittersum, M.K. van - \ 2018
European Journal of Agronomy 101 (2018). - ISSN 1161-0301 - p. 20 - 29.
Irrigation - Potential yield - Water limited yield - Water productivity - Yield gap analysis

China is enhancing potato production in both area and quantity. While the potato area is large, the actual yields remain low. Besides, the water resources used for irrigation are increasingly under pressure in potato production areas. This study aimed to assess the scope for increasing potato production in China. The key climate zones in China were identified, for which the potential yield (Yp) and water limited yield (Yw) of potato (expressed in fresh matter (FM)) were estimated by two crop growth models over 10 years (2006–2015). The Yp and Yw and yield gaps (i.e., the difference between Yp and actual yield (Ya) under irrigated conditions (Yg-p) and between Yw and Ya under rainfed conditions (Yg-w)) were evaluated at local, provincial and national level, for potatoes under both irrigated and rainfed conditions. The water availability through rainfall, water productivity (WP) and the water input gaps to realize potential rather than water-limited potato yields were identified at provincial level. The Yp in the country was on average 50.1 ton FM ha−1, and Yg-p as a percentage of Yp was 66%. At provincial level, the Yp varied from 38.8 ton FM ha−1 in Sichuan in the southwest to 66.4 ton FM ha−1 in Qinghai in the north. At national level, the Yw was 43.7 ton FM ha−1 and Yg-w as a percentage of Yw was 61%. At provincial level, the Yw was lowest in Shaanxi (27.7 ton FM ha−1) and highest in Qinghai (57.9 ton FM ha−1). Water productivity for potential yield (WP-p) ranged between 30.7 and 54 kg dry matter (DM) mm−1 ha−1 in Shaanxi and Qinghai, respectively, and for actual yield (WP-a) between 7.9 kg DM mm−1 ha−1 (Shanxi) and 22.3 kg DM mm−1 ha−1 (Sichuan). Water supply through rainfall is close to sufficient for non-water limiting potato growth in the southwest. The water input gap in the north was highest in Shaanxi (i.e., 243 mm) and lowest in Heilongjiang (i.e., 39 mm). There is a large scope to improve potato yields at current rainfall levels, especially in Qinghai and Heilongjiang in the north and in Guizhou in the southwest. By closing the exploitable yield gap (i.e., difference between 80% of Yp - or of Yw - and Ya) for the current production area, potato could contribute to an additional 1.1 and 0.9 1014 kcal, respectively, under irrigated and rainfed conditions. This is much more than that for rice (0.2 1014 kcal extra energy due to yield gap closure) under irrigated conditions, and similar or more than for maize under irrigated (1.0 1014 kcal) and rainfed (0.5 1014 kcal) conditions. We conclude that compared with the cereal staple crops, potato has a larger potential to maintain domestic food security and self-sufficiency, and to enhance water use efficiency.

LiGAPS-Beef, a mechanistic model to explore potential and feed-limited beef production 2 : sensitivity analysis and evaluation of sub-models
Linden, A. van der; Ven, G.W.J. van de; Oosting, S.J. ; Ittersum, M.K. van; Boer, I.J.M. de - \ 2018
Animal (2018). - ISSN 1751-7311 - p. 1 - 12.
beef cattle - mechanistic modelling - production ecology - sensitivity analysis - yield gap

The model LiGAPS-Beef (Livestock simulator for Generic analysis of Animal Production Systems – Beef cattle) has been developed to assess potential and feed-limited growth and production of beef cattle in different areas of the world and to identify the processes responsible for the yield gap. Sensitivity analysis and evaluation of model results with experimental data are important steps after model development. The first aim of this paper, therefore, is to identify which parameters affect the output of LiGAPS-Beef most by conducting sensitivity analyses. The second aim is to evaluate the accuracy of the thermoregulation sub-model and the feed intake and digestion sub-model with experimental data. Sensitivity analysis was conducted using a one-at-a-time approach. The upper critical temperature (UCT) simulated with the thermoregulation sub-model was most affected by the body core temperature and parameters affecting latent heat release from the skin. The lower critical temperature (LCT) and UCT were considerably affected by weather variables, especially ambient temperature and wind speed. Sensitivity analysis for the feed intake and digestion sub-model showed that the digested protein per kg feed intake was affected to a larger extent than the metabolisable energy (ME) content. Sensitivity analysis for LiGAPS-Beef was conducted for ¾ Brahman×¼ Shorthorn cattle in Australia and Hereford cattle in Uruguay. Body core temperature, conversion of digestible energy to ME, net energy requirements for maintenance, and several parameters associated with heat release affected feed efficiency at the herd level most. Sensitivity analyses have contributed, therefore, to insight which parameters are to be investigated in more detail when applying LiGAPS-Beef. Model evaluation was conducted by comparing model simulations with independent data from experiments. Measured heat production in experiments corresponded fairly well to the heat production simulated with the thermoregulation sub-model. Measured ME contents from two data sets corresponded well to the ME contents simulated with the feed intake and digestion sub-model. The relative mean absolute errors were 9.3% and 6.4% of the measured ME contents for the two data sets. In conclusion, model evaluation indicates the thermoregulation sub-model can deal with a wide range of weather conditions, and the feed intake and digestion sub-model with a variety of feeds, which corresponds to the aim of LiGAPS-Beef to simulate cattle in different beef production systems across the world.

LiGAPS-Beef, a mechanistic model to explore potential and feed-limited beef production 1 : model description and illustration
Linden, A. van der; Ven, G.W.J. van de; Oosting, S.J. ; Ittersum, M.K. van; Boer, I.J.M. de - \ 2018
Animal (2018). - ISSN 1751-7311 - p. 1 - 11.
beef cattle - growth - mechanistic modelling - production ecology - yield gap

The expected increase in the global demand for livestock products calls for insight in the scope to increase actual production levels across the world. This insight can be obtained by using theoretical concepts of production ecology. These concepts distinguish three production levels for livestock: potential (i.e. theoretical maximum) production, which is defined by genotype and climate only; feed-limited production, which is limited by feed quantity and quality; and actual production. The difference between the potential or limited production and the actual production is the yield gap. The objective of this paper, the first in a series of three, is to present a mechanistic, dynamic model simulating potential and feed-limited production for beef cattle, which can be used to assess yield gaps. A novelty of this model, named LiGAPS-Beef (Livestock simulator for Generic analysis of Animal Production Systems – Beef cattle), is the identification of the defining factors (genotype and climate) and limiting factors (feed quality and available feed quantity) for cattle growth by integrating sub-models on thermoregulation, feed intake and digestion, and energy and protein utilisation. Growth of beef cattle is simulated at the animal and herd level. The model is designed to be applicable to different beef production systems across the world. Main model inputs are breed-specific parameters, daily weather data, information about housing, and data on feed quality and quantity. Main model outputs are live weight gain, feed intake and feed efficiency (FE) at the animal and herd level. Here, the model is presented, and its use is illustrated for Charolais and Brahman × Shorthorn cattle in France and Australia. Potential and feed-limited production were assessed successfully, and we show that FE of herds is highest for breeds most adapted to the local climate conditions. LiGAPS-Beef also identified the factors that define and limit growth and production of cattle. Hence, we argue the model has scope to be used as a tool for the assessment and analysis of yield gaps in beef production systems.

Video impression “Dialogue on review Dutch food security policy”
Giller, Ken ; Ittersum, Martin van - \ 2018

Public dialogue about the IOB report “Food for thought. Review of Dutch food security policy 2012-2016”. A general video impression of the public dialogue about the IOB report “Food for thought. Review of Dutch food security policy 2012-2016”

Intensification of rice-based farming systems in Central Luzon, Philippines : Constraints at field, farm and regional levels
Silva, João Vasco ; Reidsma, Pytrik ; Lourdes Velasco, Ma ; Laborte, Alice G. ; Ittersum, Martin K. van - \ 2018
Agricultural Systems 165 (2018). - ISSN 0308-521X - p. 55 - 70.
Crop management - Farm structural change - Farmers’ objectives - Integrated assessment - Sustainable intensification - Yield gap

Understanding the opportunities for sustainable intensification requires an integrated assessment at field, farm and regional levels of past developments. Two hypotheses regarding current rice production in Central Luzon (Philippines) were developed for this purpose. First, we hypothesize that there are trade-offs between rice yields, labour productivity, gross margin and N use efficiency and, second, that farm(er) characteristics and socio-economic conditions at farm and regional level affect the management practices used by farmers. These hypotheses were tested using two household surveys characterizing rice-based farming systems in Central Luzon in terms of changes over time (1966–2012) and spatial variability. Over the past half-century there was an increase in the proportion of irrigated fields and adoption of improved varieties, which allowed the cultivation of a dry season rice crop in Central Luzon. Moreover, transplanting has been replaced by direct-seeding and herbicides substituted hand-weeding. These resulted in greater rice yields and labour productivity, and contributed to gradual transition from subsistence to commercial farming systems, as observed in the increasing proportion of hired labour and rice sold. Our results indicate the existence of a trade-off between rice yields, labour productivity and N use efficiency as yield levels maximising labour productivity and N use efficiency were ca. 25% and 35% lower than climatic potential yield in the wet and dry season, respectively. At field level, this can be explained by 1) the use of transplanting as crop establishment method, which resulted into higher yields but lower labour productivity as compared to direct-seeding, and 2) the high N application levels, which led to higher yields but lower N use efficiency. In contrast, yield levels which maximised gross margin were ca. 80% of the climatic potential in both wet and dry seasons, so there was little trade-off between rice yields and economic performance. Regarding the second hypothesis results were not always conclusive. As an example, N application per ha was negatively associated with farm size and the timing of the first fertiliser application positively associated with household size and with the number of parcels. More intensive practices, and better farm performance, were recorded in the province at the heart of the irrigation system. We thus conclude that closing rice yield gaps in the production systems of Central Luzon incurs trade-offs with environmental and social objectives at field and farm levels but less with economic objectives. However, we could not clearly show whether, and to what extent, management practices used by farmers are influenced by farm or regional level constraints.

Water productivity of rainfed maize and wheat : A local to global perspective
Rattalino Edreira, Juan I. ; Guilpart, Nicolas ; Sadras, Victor ; Cassman, Kenneth G. ; Ittersum, Martin K. van; Schils, René L.M. ; Grassini, Patricio - \ 2018
Agricultural and Forest Meteorology 259 (2018). - ISSN 0168-1923 - p. 364 - 373.
Maize - Management - Spatial framework - Water productivity - Wheat - Yield

Water productivity (WP) is a robust benchmark for crop production in relation to available water supply across spatial scales. Quantifying water-limited potential (WPw) and actual on-farm (WPa) WP to estimate WP gaps is an essential first step to identify the most sensitive factors influencing production capacity with limited water supply. This study combines local weather, soil, and agronomic data, and crop modeling in a spatial framework to determine WPw and WPa at local and regional levels for rainfed cropping systems in 17 (maize) and 18 (wheat) major grain-producing countries representing a wide range of cropping systems, from intensive, high-yield maize in north America and wheat in west Europe to low-input, low-yield maize systems in sub-Saharan Africa and south Asia. WP was calculated as the quotient of either water-limited yield potential or actual yield, and simulated crop evapotranspiration. Estimated WPw upper limits compared well with maximum WP reported for field-grown crops. However, there was large WPw variation across regions with different climate and soil (CV = 29% for maize and 27% for wheat), which cautions against the use of generic WPw benchmarks and highlights the need for region-specific WPw. Differences in simulated evaporative demand, crop evapotranspiration after flowering, soil evaporation, and intensity of water stress around flowering collectively explained two thirds of the variation in WPw. Average WP gaps were 13 (maize) and 10 (wheat) kg ha−1 mm−1, equivalent to about half of their respective WPw. We found that non-water related factors (i.e., management deficiencies, biotic and abiotic stresses, and their interactions) constrained yield more than water supply in ca. half of the regions. These findings highlight the opportunity to produce more food with same amount of water, provided limiting factors other than water supply can be identified and alleviated with improved management practices. Our study provides a consistent protocol for estimating WP at local to regional scale, which can be used to understand WP gaps and their mitigation.

Beyond the plot: technology extrapolation domains for scaling out agronomic science
Rattalino Edreira, Juan I. ; Cassman, Kenneth G. ; Hochman, Zvi ; Ittersum, Martin K. van; Bussel, Lenny van; Claessens, Lieven ; Grassini, Patricio - \ 2018
Environmental Research Letters 13 (2018)5. - ISSN 1748-9318
geospatial analysis - impact assessment - research prioritization - technology extrapolation

Ensuring an adequate food supply in systems that protect environmental quality and conserve natural resources requires productive and resource-efficient cropping systems on existing farmland. Meeting this challenge will be difficult without a robust spatial framework that facilitates rapid evaluation and scaling-out of currently available and emerging technologies. Here we develop a global spatial framework to delineate 'technology extrapolation domains' based on key climate and soil factors that govern crop yields and yield stability in rainfed crop production. The proposed framework adequately represents the spatial pattern of crop yields and stability when evaluated over the data-rich US Corn Belt. It also facilitates evaluation of cropping system performance across continents, which can improve efficiency of agricultural research that seeks to intensify production on existing farmland. Populating this biophysical spatial framework with appropriate socio-economic attributes provides the potential to amplify the return on investments in agricultural research and development by improving the effectiveness of research prioritization and impact assessment.

Closing the phosphorus cycle in a food system : insights from a modelling exercise
Kernebeek, H.R.J. van; Oosting, S.J. ; Ittersum, M.K. van; Ripoll-Bosch, R. ; Boer, I.J.M. de - \ 2018
Animal 12 (2018)8. - ISSN 1751-7311 - p. 1755 - 1765.
animal production - human diets - optimisation model - phosphorus recycling - phosphorus use

Mineral phosphorus (P) used to fertilise crops is derived from phosphate rock, which is a finite resource. Preventing and recycling mineral P waste in the food system, therefore, are essential to sustain future food security and long-term availability of mineral P. The aim of our modelling exercise was to assess the potential of preventing and recycling P waste in a food system, in order to reduce the dependency on phosphate rock. To this end, we modelled a hypothetical food system designed to produce sufficient food for a fixed population with a minimum input requirement of mineral P. This model included representative crop and animal production systems, and was parameterised using data from the Netherlands. We assumed no import or export of feed and food. We furthermore assumed small P soil losses and no net P accumulation in soils, which is typical for northwest European conditions. We first assessed the minimum P requirement in a baseline situation, that is 42% of crop waste is recycled, and humans derived 60% of their dietary protein from animals (PA). Results showed that about 60% of the P waste in this food system resulted from wasting P in human excreta. We subsequently evaluated P input for alternative situations to assess the (combined) effect of: (1) preventing waste of crop and animal products, (2) fully recycling waste of crop products, (3) fully recycling waste of animal products and (4) fully recycling human excreta and industrial processing water. Recycling of human excreta showed most potential to reduce P waste from the food system, followed by prevention and finally recycling of agricultural waste. Fully recycling P could reduce mineral P input by 90%. Finally, for each situation, we studied the impact of consumption of PA in the human diet from 0% to 80%. The optimal amount of animal protein in the diet depended on whether P waste from animal products was prevented or fully recycled: if it was, then a small amount of animal protein in the human diet resulted in the most sustainable use of P; but if it was not, then the most sustainable use of P would result from a complete absence of animal protein in the human diet. Our results apply to our hypothetical situation. The principles included in our model however, also hold for food systems with, for example, different climatic and soil conditions, farming practices, representative types of crops and animals and population densities.

Comment on Schrama et al. (2018) “Crop yield gap and stability in conventional and organic farming systems.” [Agric. Ecosyst. Environ. (256) 123–130]
Ven, G.W.J. van de; Schröder, J.J. ; Hijbeek, R. ; Velthof, G.L. ; Ittersum, M.K. van - \ 2018
Agriculture, Ecosystems and Environment 261 (2018). - ISSN 0167-8809 - p. 133 - 135.
What drives farmers to increase soil organic matter? Insights from the Netherlands
Hijbeek, R. ; Pronk, A.A. ; Ittersum, M.K. van; Berge, H.F.M. ten; Bijttebier, J. ; Verhagen, A. - \ 2018
Soil Use and Management 34 (2018)1. - ISSN 0266-0032 - p. 85 - 100.
farmers’ behaviour - farmers’ intentions - organic materials - soil conservation - soil management - soil organic matter - theory of planned behaviour

Soil organic matter (SOM) is an important resource base for arable farming. For policies on SOM to be effective, insight is needed on why and under which conditions farmers are willing to increase SOM content. This study used the theory of planned behaviour to analyse what prevents or encourages Dutch farmers to increase the SOM content of their fields. In an online survey, 435 arable farmers were asked questions to understand their attitude (perceived benefits), subjective norm (social pressure) and perceived behavioural control (anticipated impediments and obstacles) related to management of SOM. Farmers’ answers were related to their intention to increase SOM content, use of organic materials and perceived increase in SOM content. Our results showed that Dutch farmers are well aware of the possible benefits of SOM content for crop productivity. Farmers’ attitude, subjective norm and perceived decrease in SOM content were significantly related to their intention to increase SOM content. In our farm survey, this intention was very strong: 90% of the farmers stated a high or very high intention to increase the SOM content of their fields. A higher intention to increase SOM content was correlated with the use of organic materials as expressed as total and effective C (P = 0.003 and P = 0.002, respectively), but this did not lead to a perceived increase in SOM content. From a farmer's point of view, this indicates that increasing SOM content is to a large degree beyond their direct influence. The Dutch Manure and Fertiliser Act, costs of organic inputs and the need to cultivate profitable crops (such as potatoes or sugar beet) were indicated as important impeding factors for increasing SOM content.

Intercropping with wheat lowers nutrient uptake and biomass accumulation of maize, but increases photosynthetic rate of the ear leaf
Gou, Fang ; Ittersum, Martin K. Van; Couëdel, Antoine ; Zhang, Yue ; Wang, Yajun ; Putten, Peter E.L. van der; Zhang, Lizhen ; Werf, Wopke van der - \ 2018
AoB Plants 10 (2018)1. - ISSN 2041-2851
Intercropping is an ancient agricultural practice that provides a possible pathway for sustainable increases in crop yields. Here, we determine how competition with wheat affects nutrient uptake (nitrogen and phosphorus) and leaf traits, such as photosynthetic rate, in maize. In a field experiment, maize was planted as a sole crop, in three different intercrop configurations with wheat (a replacement intercrop and two add-row intercrops), and as a skip-row system with one out of each three maize rows omitted. Nitrogen and phosphorus uptake were determined at flowering and maturity. Specific leaf area, leaf nitrogen concentration, chlorophyll content and photosynthetic rate of the ear leaf were determined at flowering. Nitrogen and phosphorus concentrations were significantly lower in intercropped maize than in sole maize and skip-row maize at flowering, but these differences were smaller at maturity. At flowering, specific leaf area was significantly greater in intercrops than in skip-row maize. Leaf nitrogen concentration was significantly lower in add-row intercrops than in sole maize, skip-row maize or maize in the replacement intercrop. Leaf chlorophyll content was highest in sole and skip-row maize, intermediate in maize in the replacement intercrop and lowest in maize grown in add-row intercrops. On the contrary, photosynthetic rate was significantly higher in the replacement intercrop than in sole maize, skip-row maize and the intercrop with an additional maize row. The findings indicate that competition with intercropped wheat severely constrained nutrient uptake in maize, while photosynthetic rate of the ear leaf was not negatively affected. Possible mechanisms for higher photosynthesis rate at lower leaf nitrogen content in intercropped maize are discussed.
LiGAPS-Beef 2018
Linden, A. van der; Ven, G.W.J. van de; Oosting, S.J. ; Ittersum, M.K. van; Boer, I.J.M. de - \ 2018
LiGAPS-Beef is a mechanistic model to assess potential and feed-limited beef production in different beef production systems across the world. The model is one of the first using concepts of production ecology to simulate livestock production. LiGAPS-Beef consists of a thermoregulation sub-model, a feed intake and digestion sub-model, and an energy and protein utilization sub-model. Energy and protein flows are included. Livestock production can be assessed for individual animals and herds. LiGAPS-Beef simulates cattle growth based on defining growth factors (genotype or breed and climate) and limiting growth factors (feed quality and feed quantity). The model can be used to assess yield gaps in beef production systems, and to explore improvement options for yield gap mitigation.
Genetische vooruitgang sneller dan opbrengststijging - Maximale opbrengst vaak niet rendabel
Rijk, Bert ; Ittersum, Martin van - \ 2018

Nieuwe rassen van de belangrijkste akker­bouwgewassen bieden nog steeds een verdere potentiele opbrengststijging. Het gat tussen de behaalde opbrengsten en de potentiele opbrengsten wordt echter steeds groter. Dat blijkt uit een analyse uitgevoerd door WUR PAGV.

Nieuwe rassen van de belangrijkste akker­bouwgewassen bieden nog steeds een verdere potentiele opbrengststijging. Het gat tussen de behaalde opbrengsten en de potentiele opbrengsten wordt echter steeds groter. Dat blijkt uit een analyse uitgevoerd door WUR PAGV.

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In de internationale literatuur duiken steeds vaker artikelen op waaruit blijkt dat praktijkopbrengsten in hoogproductieve landen stagneren. Reden genoeg voor WUR-onderzoekers om een eerder onderzoek aan rassenproeven in Nederland over de jaren tot 2010 te herhalen met de nieuwste gegevens. Met een specifieke statistische analyse van rassenproeven kan de invloed van veranderend klimaat, maar ook de CO2-concentratie in de lucht (E) en gewijzigde teeltmaatregelen (M) gescheiden wordenvan het effect vande introductie van nieuwe rassen (G).De opbrengst van een gewas hangt af van de genetische eigenschappen van het ras, het klimaat en de teeltmaatregelen (dit wordt afgekort als GxExM = genetics x environment x management).

Uit analyse van rassenproeven die zijn uitgevoerd van 1980 tot 2016 in wintertarwe, zomergerst, zetmeelaardappelen en suikerbieten blijkt dat het opbrengend vermogen van nieuwe rassen van deze gewassen blijft stijgen, los van weers-en klimaatinvloeden en verbeterd gewasmanagement.

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