H.H. van Laar

Products, requirements and efficiency of biosynthesis: a quantitative approach

Abstract The question of how many grams of an organism can grow heterotrophically from only 1·0 g of glucose and adequate minerals has been put forward many times. Only a few attempts have been made to answer this question theoretically and these attempts were rather rough. In this paper, it is demonstrated that the yield of a growth process may be accurately computed by considering the relevant biochemistry of conversion reactions and the cytological implications of biosynthesis and growth. Oxygen consumption and carbon dioxide production by these processes are also computed. The weight of the biomass synthesized from 1·0 g of substrate and the quantities of gases exchanged are independent of temperature. These results are obtained by adding the individual equations describing the formation of each compound synthesized by the organism from the substrate supplied. The sum represents an equation which accounts for all substrate molecules required for biosynthesis of the carbon skeletons of an end-product, whose chemical composition is given. It is then calculated how much energy is required for the non-synthetic processes which form a part of biosynthesis, such as intra- and intercellular transport of molecules and maintenance of RNA and enzymes. The additional amount of substrate required to provide this energy by combustion is easily calculated. Adding this substrate to the amount used for skeleton synthesis gives an overall equation which quantifies the substrate and oxygen demand as well as carbon dioxide evolution during biosynthesis of 1·0 g biomass. For example, it requires 1·34 g of glucose with adequate ammonia and minerals to synthesize 1·0 g maize plant biomass in darkness; during this process 0·14 g oxygen are consumed and 0·24 g carbon dioxide are produced. It has been described elsewhere that similar results were obtained experimentally with growing plants. Such results depend considerably upon the chemical composition of the biomass being synthesized and upon the state (oxidized or reduced) of the nitrogen source. Other parameters, such as the number of ATP molecules required for protein synthesis, the possibility for utilization of alternative pathways for synthesis or energy production, the presence or absence of compartmentation of synthetic processes and variations in the P/O ratio between two and three, under many conditions affect results of the computation less than 10%. Since maintenance of cellular structures is not considered, the approach concerns the gross yield of biosynthesis. It predicts therefore the dry matter yield of heterotrophic cells from a given quantity of substrate at high relative growth rates.

The `School of de Wit' crop growth simulation models: A pedigree and historical overview

In this paper, a pedigree of the crop growth simulation models by the ‘School of de Wit’ is presented. The origins and philosophy of this school are traced from de Wits classical publication on modelling photosynthesis of leaf canopies in 1965. It is shown how changing research goals and priorities over the years have resulted in the evolution of a pedigree of models that are similar in philosophy but differ in level of complexity, the processes addressed and their functionality. In the beginning, modelling was motivated by the quest for scientific insight and the wish to quantify and integrate biophysical processes to explain the observed variation in crop growth. Later, the emphasis of, and funding for, agricultural research shifted towards putting acquired insights to practical and operational use. Model development became led by a demand for tactical and strategic decision support, yield forecasting, land zonation and explorative scenario studies. Modelling developments for different production situations are illustrated using the models the authors consider most important, i.e. BACROS, SUCROS, WOFOST, MACROS and LINTUL, but reference is also made to other models. Finally, comments are made about the usefulness and applicability of these models after nearly 30 years of development, and some future courses of action are suggested.

Applications of systems approaches at the field level

Preface. The Challenge of Integrating Systems Approach in Plant Breeding: Opportunities, Accomplishments, and Limitations P.K. Aggarwal, et al. Using Systems Approaches for Targeting Site Specific Management on Field Level J. Bouma, et al. New High-Yielding, Weed Competitive Rice Plant Types Drawing from O. sativa and O. glaberrima Genepools M. Dingkuhn, et al. Improving Rice Tolerance to Barnyardgrass through Early Crop Vigour: Simulations with INTERCOM J.L. Lindquist, M.J. Kropff. Recent Advances in Breeding for Drought Tolerance in Maize G.O. Edmeades, et al. Potential Yield of Irrigated Rice in African Arid Environments M. Dingkuhn, A. Sow. Assessing the Potential Yield of Tropical Crops: Role of Field Experimentation and Simulation R.C. Muchow, M.J. Kropff. Evaluation of the CROPGRO-Soybean Model over a Wide Range of Experiments K.J. Boote, et al. Adaptation of the CROPGRO Model to Simulate the Growth of Field-Grown Tomato J.M.S. Scholberg, et al. A Modified Version of CERES to Predict the Impact of Soil Water Excess on Maize Crop Growth and Development J.I. Kizaso, J.T. Ritchie. Mitigating Climate Change Effects on Rice Yield S. Mohandass, T.B. Ranganathan. Competition for Light in Windbreak-Millet Systems in the Sahel M. Mayus, et al. Crop Models and Precision Agriculture M.Y.L. Boone, et al. A Conceptual Model for Sodium Uptake and Distribution in Irrigated Rice F. Asch, et al. Using Decision Support Systems to Optimize Barley Management on Spatial Variable Soil H.W.G. Booltink, J. Verhagen. Application of SOYGRO in Argentina S. Meira, E. Guevara. Modeling the Effect of Nitrogen on Rice Growth and Development T. Hasegawa, T. Horie. Optimization of Nitrogen Fertilizer Application to Irrigated Rice R.N. Dash, et al. Simulating Rice Leaf Area Development and Dry Matter Production in Relation to Plant N and Weather M. Ohnishi, et al. Influence of Split Application of Nitrogen on Foliar N Content, Photosynthesis, Dry Matter Production and Yield in Short and Medium Duration Rice Cultivars C. Vijayalakshmi, M. Nagarajan. Systems Approaches to Improve Nitrogen Management in Rice B. Mishra. Use of Simulation Models to Optimize Fungicide Use for Managing Tropical Rice Blast Disease S.B. Calvero, P.S. Teng. Yield Gap Analysis of Rainfed Lowland Systems to Guide Rice Crop and Pest Management H.O. Pinnschmidt, et al. Quantification of the Effects of Bacterial Blight Disease on Rice Crop Growth and Grain Yield P.R. Reddy. Better Biological Control by a Combination of Experimentation and Modelling J.C. Van Lenteren, H.W.J. Van Roermund. Quantitative Evaluation of Growth and Yield of Rice Plants Infested with Rice Planthoppers T. Watanabe, et al. Addressing Sustainability of Rice--Wheat Systems: Analysis of Long-Term Experimentation and Simulation J. Timsina, et al. Systems Approach in the Design of Soil and Water Conservation Measures L. Stroosnijder, P. Kiepe. Farming Systems for Sustainable Agriculture and Environmental Quality R.S. Kanwar, et al. Harnessing Crop Research Data to Develop Expert Systems K. Muralidharan, E.A. Siddiq. Comparison of Predictions and Observations to Assess Model Performance: A Method of Empirical Validation P.L. Mitchell, J.E. Sheehy. Acronyms. Subject Index.

Integration of Systems Network (SysNet) tools for regional land use scenario analysis in Asia

Abstract This paper introduces the approach of the Systems research Network (SysNet) for land use planning in tropical Asia with a focus on its main scientific–technical output: the development of the land use planning and analysis system (LUPAS) and its component models. These include crop simulation models, expert systems, GIS, and multiple goal linear programming (MGLP) models for land evaluation and optimization. LUPAS was designed as a decision support system (DSS) for strategic land use planning. Integration of LUPAS components in four case studies was performed in a network with national research teams and local stakeholders. This network allowed iterative evaluation and refinement of LUPAS for scenario analysis on technical and policy changes. Several interactive sessions with stakeholders led to more detail in scenarios (goals and constraints), model features and databases. To facilitate negotiation among stakeholders, the MGLP user interface (UI) was developed. In interactive sessions, goal restrictions are tightened to quantify trade-offs between conflicting goals. Choice and degree of tightening reflect the specific priorities for sustainable land use. The development of LUPAS is exemplified for one case study, Ilocos Norte, Philippines. Weak points of the system include inadequate spatial differentiation of socio-economic characteristics, scarce database for quantifying perennials and mixed cropping systems, and insufficient consideration of long-term effects of production technologies on resource quality. However, a promising perspective for effective policy support lies in the possible link of the regional LUPAS approach with farm household models.

Photosynthesis, CO2 and Plant Production

Agricultural production can be increased through better plant characteristics obtained either through breeding or through better growing conditions, both in the soil and above ground. In the chain of events necessary for plant growth, photosynthesis stands at the beginning as the primary conversion of light energy to chemical energy stored in organic substances. This paper deals with the influence of photosynthetic performance on the eventual dry matter production of plants. The approach used is mechanistic and quantitative, and, because the number of interacting factors is large, a simulation method is used. Our simulation model is essentially BACROS (de Wit et al., 1978), modified to the present (1983) version in a number of ways indicated below. We consider characteristics of C3 plants only.

Design of weed management systems with a reduced reliance on herbicides poses new challenges and prerequisites for modeling crop–weed interactions

Abstract Ecophysiological models for interplant competition were first developed in the early 1980s to obtain a better understanding of the harmful effect of weeds on crop productivity. The models were developed from simulation models of monoculture crops; each competing species was represented by its own growth model, which were then linked by additional routines to account for the distribution of resources over competing species. Initially the models were used for the construction of more robust damage relationships to support rational decision making on the use of herbicides. At present, apart from a need to reduce the use of herbicides, the design of weed management systems with a reduced reliance on herbicides is advocated. As a result, the weed problem should be envisaged in a different perspective. Rather than focusing only on detrimental effects in current crops, main emphasis should shift towards the management of weed populations and weed management itself should become an integrated component of crop management. For the development of these alternative management systems, specific improvements with respect to prevention, alternative control technology and decision making seem promising. The new challenges for modeling crop–weed interactions and prerequisites for crop–weed competition models that follow from these developments are discussed.

Effect of Lactation Stage on the Odd- and Branched-Chain Milk Fatty Acids of Dairy Cattle Under Grazing and Indoor Conditions

The pattern of odd- and branched-chain fatty acids (OBCFA) in milk fat reflects rumen microbial activity and proportions of different rumen microbial groups. Therefore, these milk fatty acids (FA) are used to predict rumen proportions of volatile fatty acids, duodenal flow of microbial protein, and occurrence of rumen acidosis. However, current models do not correct for the potential effects of lactation stage on the level of OBCFA in milk fat. Hence, the objectives of this study were 1) to describe progressive changes related to lactation stage in concentrations of milk FA, with emphasis on the OBCFA, using the incomplete gamma function of Wood, and 2) to analyze whether lactation curves of milk FA on the one hand and milk production or milk fat content on the other hand coincide through evaluation of the correlation between the parameters of the Wood functions fitted to individual animal data. Data were collected from 2 trials in which milk FA during lactation were monitored. The first experiment was a stable trial with 2 groups of 10 cows receiving 2 dietary treatments from wk 1 to 40 of lactation. The second experiment was a grazing trial with 9 cows that were followed during the first 18 wk of lactation. Lactation curves of milk production, milk fat content, and individual milk FA were developed using the incomplete gamma function of Wood for each of the 3 dietary strategies separately. For almost all of the milk FA, lactation curve shapes were similar for all 3 dietary treatments. The OBCFA with chain lengths of 14 and 15 carbon atoms followed the lactation curves of the short- and medium-chain milk FA, which increased in early lactation. The OBCFA with chain length of 17 carbon atoms decreased during the early lactation period, following the pattern of milk long-chain fatty acids. The short- and medium-chain milk FA and OBCFA in the early lactation period seemed to be negatively correlated with the starting milk production and milk fat content, but correlations were modest. Information of milk FA lactation curves should be incorporated in predictive and classification models based on these milk FA, to improve their performance.

Analysing crop yield and plant quality in an intercropping system using an eco-physiological model for interplant competition

An eco-physiological model was used to improve understanding of interplant competition based on physiological, morphological and phenological processes. The model was parameterised based on characteristics of the plants in monocultures and its performance was evaluated for the crop mixtures using experimental data from different growing seasons. A light interception routine accounting for row-geometry was compared to a routine assuming a homogeneous horizontal leaf area distribution. The models simulated the light distribution among the species equally well. The production of the two crops in the mixture was accurately simulated using parameter values based on monoculture growth characteristics. Morphological characteristics of the species such as the relative growth rate of leaf area during early growth and specific leaf area largely determined the competitive strength of the species. Dry matter production of the species, particularly if grown in mixture, was highly sensitive to maximum plant height and radiation use efficiency. Celery was found to be a stronger competitor than leek and clear responses of quality characteristics to plant density in monoculture and mixtures were observed. The model was used to determine ranges of plant densities that enable the intercropping system to meet current quality standards of the component crops.

Science for agriculture and rural development in low-income countries

Preface, Executive Summary, List of Abbreviations. 1. Agriculture in a dynamic world, R.P. Roetter, H. Van Keulen, J. Verhagen and M. Kuiper. 2. Historical context of agricultural development, H. Van Keulen. 3. Food security, R.P. Roetter and H. Van Keulen. 4. Agriculture and environment, J. Verhagen, H. Wosten and A. De Jager. 5. Rural livelihoods: Interplay between farm activities, non-farm activities and the resource base, M. Kuiper, G. Meijerink and D. Eaton. 6. Lessons learned, R.P. Roetter, M. Kuiper, H. Van Keulen, J. Verhagen and G. Meijerink. 7. Project assessments, A. De Jager, C. Ritsema, M. Mosugu, G. Meijerink, P. Van den Brink, H. Van den Bosch, E. Van der Elsen, R.P. Roetter, S. Van Wijk, S. Verzandvoort-Van Dijck, C.A. Van Diepen and B. Kamphuis. Project NUTSAL, Project EroChinut, Project PIMEA, Project INMASP, Project MAMAS, Project EROAHI, Project Himalaya, Project IRMLA, Project VEGSYS, Project VINVAL, Project RMO-Beijing, Project SEARUSYN

Effects of dietary starch content and rate of fermentation on methane production in lactating dairy cows

The objective of this study was to investigate the effects of starch varying in rate of fermentation and level of inclusion in the diet in exchange for fiber on methane (CH4) production of dairy cows. Forty Holstein-Friesian lactating dairy cows of which 16 were rumen cannulated were grouped in 10 blocks of 4 cows each. Cows received diets consisting of 60% grass silage and 40% concentrate (dry matter basis). Cows within block were randomly assigned to 1 of 4 different diets composed of concentrates that varied in rate of starch fermentation [slowly (S) vs. rapidly (R) rumen fermentable; native vs. gelatinized corn grain] and level of starch (low vs. high; 270 vs. 530g/kg of concentrate dry matter). Results of rumen in situ incubations confirmed that the fractional rate of degradation of starch was higher for R than S starch. Effective rumen degradability of organic matter was higher for high than low starch and also higher for R than S starch. Increased level of starch, but not starch fermentability, decreased dry matter intake and daily CH4 production. Milk yield (mean 24.0±1.02kg/d), milk fat content (mean 5.05±0.16%), and milk protein content (mean 3.64±0.05%) did not differ between diets. Methane expressed per kilogram of fat- and protein-corrected milk, per kilogram of dry matter intake, or as a fraction of gross energy intake did not differ between diets. Methane expressed per kilogram of estimated rumen-fermentable organic matter (eRFOM) was higher for S than R starch-based diets (47.4 vs. 42.6g/kg of eRFOM) and for low than high starch-based diets (46.9 vs. 43.1g/kg of eRFOM). Apparent total-tract digestibility of neutral detergent fiber and crude protein were not affected by diets, but starch digestibility was higher for diets based on R starch (97.2%) compared with S starch (95.5%). Both total volatile fatty acid concentration (109.2 vs. 97.5mM) and propionate proportion (16.5 vs. 15.8mol/100mol) were higher for R starch- compared with S starch-based diets but unaffected by the level of starch. Total N excretion in feces plus urine and N retained were unaffected by dietary treatments, and similarly energy intake and output of energy in milk expressed per unit of metabolic body weight were not affected by treatments. In conclusion, an increased rate of starch fermentation and increased level of starch in the diet of dairy cattle reduced CH4 produced per unit of eRFOM but did not affect CH4 production per unit of feed dry matter intake or per unit of milk produced.