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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    Understanding the productivity of cassava in West Africa
    Ezui, Kodjovi Senam - \ 2017
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Linus Franke; A. Mando. - Wageningen : Wageningen University - ISBN 9789463430470 - 183
    manihot esculenta - cassava - crop production - rainfed agriculture - drought - crop yield - water use efficiency - radiation use efficiency - fertilizers - togo - ghana - west africa - manihot esculenta - cassave - gewasproductie - regenafhankelijke landbouw - droogte - gewasopbrengst - watergebruiksrendement - stralingsbenuttigingsefficiëntie - kunstmeststoffen - togo - ghana - west-afrika

    Drought stress and sub-optimal soil fertility management are major constraints to crop production in general and to cassava (Manihot esculenta Crantz) in particular in the rain-fed cropping systems in West Africa. Cassava is an important source of calories for millions of smallholder households in sub-Sahara Africa. The prime aim of this research was to understand cassava productivity in order to contribute to improving yields, food security and farm incomes in rain-fed cassava production systems in West Africa. A long-term goal was to contribute to a decision support tool for site-specific crop and nutrient management recommendations. Firstly, we studied farmers’ perception of cassava production constraints, assessed drivers of diversity among households and analysed the suitability of farmers’ resource endowment groups to the intensification of cassava production. The results indicate that farmers perceived erratic rainfall and poor soil fertility to be prime constraints to cassava production. The agricultural potential of the area and the proximity to regional markets were major drivers for the adoption of crop intensification options including the use of mineral and organic fertilizers. While the use of mineral and organic fertilizers was common in the Maritime zone that had a low agricultural potential, storage roots yields were below the national average of 2.2 Mg dry matter per hectare, and average incomes of 0.62, 0.46 and 0.46 US$ per capita per day for the high, medium and low farmer resource groups (REGs – HRE, MRE and LRE, respectively) were below the poverty line requirement of 1.25 US$. In the high agricultural potential Plateaux zone, HRE and MRE households passed this poverty line by earning 2.58 and 2.59 US$ per capita per day, respectively, unlike the LRE households with 0.89 US$ per capita per day. Secondly, we investigated the effects of mineral fertilizer on nutrient uptake, nutrient physiological use efficiency and storage roots yields of cassava since soil fertility was a major issue across the zones. We used an approach based on the model for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). This model was successfully adapted for cassava and it appropriately assessed the response of cassava to N, P and K applications, especially in years with good rainfall. Under high drought stress, the model overestimated cassava yields. Thirdly, we investigated the impact of balanced nutrition on nutrient use efficiency, yield and return on investment compared to blanket fertilizer use as commonly practiced in cassava production systems in Southern Togo, and in Southern and Northern Ghana. The balanced nutrition approach of the QUEFTS model aimed to maximize simultaneously nutrient use efficiency of N, P and K in accordance with the plant’s needs. Larger nutrient use efficiencies of 20.5 to 23.9 kg storage root dry matter (DM) per kilo crop nutrient equivalent (1kCNE of a nutrient is the quantity of that nutrient that has the same effect on yield as 1 kg of N under balanced nutrition conditions) were achieved at balanced nutrition at harvest index (HI) of 0.50 compared to 20.0 to 20.5 kg storage root DM per kilo CNE for the blanket rates recommended by national research services for cassava production. Lower benefit:cost ratios of 2.4±0.9 were obtained for the blanket fertilizer rates versus 3.8±1.1 for the balanced fertilizer rates. Our study revealed that potassium (K) was a major yield limiting factor for cassava production, especially on the Ferralsols in Southern Togo. Hence, we fourthly studied the effect of K and its interaction with nitrogen (N), phosphorus (P), and the timing of harvest on the productivity of cassava in relation to the effects of K on radiation use efficiency (RUE), light interception, water use efficiency (WUE) and water transpiration. The results suggest that K plays a leading role in RUE and WUE, while N is the leading nutrient for light interception and water transpiration. Potassium effects on RUE and WUE depended on the availability of N and harvest time. Values of RUE and WUE declined with harvest at 4, 8 and 11 months after planting. Thus, enhanced K management with sufficient supply of N during the early stage of development of cassava is needed to maximize RUE and WUE, and consequently attain larger storage root yields. Given that erratic rainfall was another major constraint to cassava production according to the results of the farm survey, and due to the inability of QUEFTS modelling to assess drought effects on cassava yield successfully, another modelling approach based on light interception and utilization (LINTUL) was used. We quantified drought impacts on yields and explored strategies to improve yields through evaluation of planting dates in Southern Togo. The evaluation of the model indicated good agreement between simulated and observed leaf area index (Normalised Root Mean Square Error - NRMSE - 17% of the average observed LAI), storage roots yields (NRMSE 5.8% of the average observed yield) and total biomass yield (NRMSE 5.8% of the average observed). Simulated yield losses due to drought ranged from 9-60% of the water-limited yields. The evaluation of planting dates from mid-January to mid-July indicated that the best planting window is around mid-February. Higher amount of cropping season rainfall was also achieved with early planting. These results contradict current practices of starting planting around mid-March to mid-April. However, the results indicate the possibility to increase cassava yields with early planting, which led to less yield losses due to drought. By contrast, late planting around June-July gave larger potential yields, and suggested these periods to be the best planting window for cassava under irrigated conditions in Southern Togo. This shows that appropriate water control and planting periods can contribute to attaining larger yields in Southern Togo. Further improvement of the LINTUL model is required towards using it to assess water-limited yield, which can be used as boundary constraint in QUEFTS to derive site-specific fertilizer requirements for enhanced cassava yield and returns on investments in West Africa.

    Improving radiation use efficiency in greenhouse production systems
    Li, Tao - \ 2015
    Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Ep Heuvelink. - Wageningen : Wageningen University - ISBN 9789462572577 - 156
    glastuinbouw - kassen - gewasfysiologie - agrarische productiesystemen - gewasproductie - stralingsbenuttigingsefficiëntie - straling - fotosynthese - licht - gebruiksefficiëntie - greenhouse horticulture - greenhouses - crop physiology - agricultural production systems - crop production - radiation use efficiency - radiation - photosynthesis - light - use efficiency


    A large increase in agricultural production is needed to feed the increasing world population with their increasing demand per capita. However, growing competition for arable land, water, energy, and the degradation of the environment impose challenges to improve crop production. Hence agricultural production efficiency needs to increase. Greenhouses provide the possibility to create optimal growth conditions for crops, thereby improving production and product quality. Light is the driving force for plant photosynthesis and in greenhouse horticulture, light is often the most limiting factor for plant growth. Therefore, improving radiation use efficiency (RUE) in greenhouse production systems is imperative in order to improve plant growth and production. The objective of this thesis is to obtain insight in improving RUE in greenhouse production systems through better understanding of crop physiology. Three aspects related to RUE have been studied in this thesis, 1) improving light distribution in the crop canopy; 2) allowing more light in the greenhouse during summer; and 3) balancing the source and sink strength during plant growth.

    Light is heterogeneously distributed in the crop canopy. Due to the saturating response of leaf photosynthesis rate to light, a more homogeneous light distribution in the canopy will result in a higher crop photosynthesis. In Chapter 2, the effect of diffuse glass on spatial light distribution in a fully developed tomato canopy and its direct and indirect effects on crop photosynthesis were explored. Diffuse glass, which transforms a portion of direct solar light into diffuse light without influencing the light transmissivity of the glass, was applied as greenhouse cover. Under diffuse glass cover, light was more evenly distributed (in both horizontal and vertical direction) within the canopy compared with plants grown under conventional clear glass cover. Besides a more uniform light distribution, diffuse glass also resulted in higher leaf photosynthetic capacity in the middle of the crop canopy and in a higher leaf area index (LAI). The higher leaf photosynthetic capacity was positively correlated with a higher leaf total nitrogen and chlorophyll content. Moreover, lower leaf temperature and less photo-inhibition of top canopy leaves were observed under diffuse glass cover when global radiation was high. Total crop photosynthesis between 1st April and 1st October was enhanced by 7.2 % under diffuse glass. This enhancement mainly resulted from four factors (in order of decreasing importance): a more homogeneous horizontal light distribution, a higher leaf photosynthetic capacity, a more uniform vertical light distribution and a higher LAI.

    In summer growers of shade tolerant pot-plants often apply shading screens in the greenhouse or white wash on the greenhouse cover in order to avoid leaf or flower damage caused by high light. Shading carries a penalty on potential crop growth which is positively related to the amount of light that can be captured. Considering the advantageous properties of diffuse glass cover, i.e. a more homogeneous light distribution, a lower leaf temperature and less photo-inhibition when global radiation is high, in Chapter 3 we tested the feasibility of allowing more light (i.e. less shading) via diffuse glass cover for cultivation of shade tolerant pot-plants during summer. Two Anthurium andreanum cultivars (Pink Champion and Royal Champion) were grown in 3 greenhouse compartments. Under similar DLI [7.5 mol m-2 d-1 PAR (photosynthetic active radiation)], diffuse glass cover resulted in 8 % higher crop RUE (i.e. dry mass production per unit intercepted light) in ‘Royal Champion’ compared with clear glass cover treatment, which consequently resulted in higher total biomass production. This effect was not observed in ‘Pink Champion’. Under diffuse glass cover, high DLI (10 mol m-2 d-1 PAR) resulted in 20-23 % higher total biomass production in both cultivars compared with low DLI (7.5 mol m-2 d-1 PAR), this mainly resulted from the higher cumulative intercepted light. No flower or leaf damage was observed in these treatments. High DLI even resulted in more compact plants as indicated by a higher ratio of aboveground fresh mass to plant height.

    In Chapter 4, we addressed a question resulting from Chapter 3, i.e. why the stimulating effect of diffuse light on crop RUE in anthurium pot-plants is cultivar specific? We excluded the fraction of canopy light interception and steady-state leaf photosynthesis as potential explanations, and explained it from instantaneous leaf photosynthesis which closely correlates with the temporal light distribution. Diffuse glass cover smoothed the variation of temporal light distribution at a given point on a leaf during a clear day, which consequently resulted in less temporal variation of stomatal conductance in ‘Royal Champion’ which had stomata showing a fast-response to the variation in light intensity. As stomata are the gateway for CO2 uptake, less variation in stomatal conductance imposed less limitation for leaf photosynthesis under diffuse glass cover, thereby resulting in a higher crop RUE. For ‘Pink Champion’, however, stomata were less responding to variations in light intensity. Therefore, stomata imposed only a marginal limitation on leaf photosynthesis even under clear glass cover where the temporal incident light intensity varied substantially due to the shadow cast by the greenhouse construction parts and equipment.

    Application of supplementary assimilation light in greenhouses is rapidly increasing. The beneficial effect of supplementary assimilation light is determined by the balance between assimilate production in source leaves and the overall capacity of the plant to use these assimilates. Therefore, it is important to identify the source-sink balance during plant growth. In Chapter 5, three tomato cultivars with different potential fruit size [‘Komeett’ (large size); ‘Capricia’ (medium size); ‘Sunstream’ (small size, cherry tomato)] were grown under commercial crop management. We estimated the source-sink ratio from the early growth stage to fully fruiting stage through experimentation and model simulation. Carbohydrate content of leaves and stems were periodically determined. Tomato plants showed a period of sink limitation (‘Komeett’ and ‘Capricia’) or came close to sink limitation (‘Sunstream’) during the early growth stage under ample natural irradiance (early September) as indicated by a source-sink ratio higher than or close to 1. Fruiting tomato plants were source-limited as indicated by an extremely low source-sink ratio (average source-sink ratio from 50 days after planting onwards was 0.17, 0.22 and 0.33 for ‘Komeett’, ‘Capricia’ and ‘Sunstream’, respectively). During the fully fruiting stage, the source-sink ratio was negatively correlated with the potential fruit size when commercial fruit load was maintained. Carbohydrate content in tomato stems and leaves increased linearly with plant source-sink ratio.

    The experiments and results described in this thesis provide insights for improving RUE in greenhouse production systems. The main achievements and limitations as well as practical applications are discussed in Chapter 6.

    Brandstof kweken biedt zicht op schone toekomst
    Klein Lankhorst, R.M. - \ 2013
    Milieu : opinieblad van de Vereniging van Milieuprofessionals 2013 (2013)sept. - ISSN 1873-5436 - p. 11 - 13.
    zonne-energie - biobrandstoffen - biobased economy - duurzame energie - fotosynthese - stralingsbenuttigingsefficiëntie - cyanobacteriën - solar energy - biofuels - biobased economy - sustainable energy - photosynthesis - radiation use efficiency - cyanobacteria
    De zon is onze perfecte duurzame energiebron die we kunnen aftappen via fotosynthese. Planten doen dit al van nature, maar lang niet efficiënt genoeg. Daarom werkt het bedrijf BioSolar Cells aan de ontwikkeling van Solar Fuels: brandstoffen die rechtstreeks, zonder eerst biomassa te maken, worden gemaakt uit zonlicht, water en CO2. Dit kan met hoge efficiëntie en ondervangt bovendien een aantal knellende problemen met het gebruik van biomassa.
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