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«International 17 Workshop th Nitrogen The was jointly organised by Teagasc and AFBI Printed by Print Depot Suggested citation Authors, 2012. Title ...»

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2. Materials & Methods Lettuce [(Lactuca sativa L. var. acephala type Batavia) cv. Rubia flavia] plants were grown in floating system under natural conditions in a greenhouse equipped an environmental parameters control station. Plants were grown in three nutrition solutions containing 2, 10 or 20 mM N-NO3 while other macroelements expressed in mM were: 2.8 P, 8.4 K, 3.5 Ca, 1.4 Mg and Hoagland’s concentration for micronutrients. Nitrate content was measured by spectrophotometer using the salicylic-sulphuric acid method with slight modifications (Cataldo et al., 1975). Nitrate reductase activity in vivo was determined using leaf discs, about 0.3 g each sample. The assay buffer contained 100 mM phosphate buffer pH 7.5, 30 mM KNO3 and 5% (v/v) propanol. The leaf discs were placed in the assay buffer and were incubated at 30 °C for 15 min. in a water-bath and then boiled. Blank samples were immediately boiled and incubated. In all reactions, the nitrite content was measured using equal volume of color development reagent (1% sulfanilamide in 3N HCl and 0.02% N-(1-naphthyl)-ethylenediaminehydrochloride). The reaction mixtures were incubated at room temperature for 15 min and absorbance was read at 540 nm. The amount of nitrite was calculated by a calibration curve obtained with standard solutions containing 0, 25, 50, 100 and 120 nmol KNO2. Sucrose and reducing sugars have been extracted and determined as reported in Trivellini et al. (2011). Data were subjected to ANOVA analysis and differences among means were determined with Bonferroni’s post-test.

3. Results & Discussion The yield of lettuce grown in the different nutrient solutions were not affected by nitrate concentrations and ranged from 1931 to 2680 g m-2 (Table 1). The leaf nitrates content was not statistical different among the treatments. The lowest nitrate content was 1412 and the highest 2643

Nitrogen Workshop 2012

mg kg-1 FW. The nitrate reductase activity in vivo determined 11:30 A.M. in the three nitrate concentrations showed that the lowest value was found at 10 mM and the highest was found at 20 mM. The nitrite content decreased by increasing the nitrate concentration in the nutrient solution.

The higher amount of nitrite was found at 2 mM, while at 10 or 20 mM the nitrite were 14.39 and

8.62 ng g-1 FW, respectively (Table 1). The sucrose content increased with nitrate concentration in the nutrient solution (Figure 1A). An analogous trend was observed for reducing sugars, as plants grown in higher nitrate concentrations had similar reducing sugars content (Figure 1B).

Table 1. Yield, nitrates, nitrate reductase activity and nitrites in lettuce plants grown in floating system with 2, 10 or 20 mM nitrate in the nutrient solution.

Values are means with standard errors (n=4).

–  –  –

Figure 1. A) Sucrose content and B) reducing sugars in leaves of lettuce baby leaf grown in floating system with different nitrate concentration in the nutrient solution.

Data reported are means with standard errors (n=4). Different letters indicate statistical differences for P0.05. Different letters indicate statistical difference for P0.05.

4. Conclusions Lettuce baby leaf can grow with nitrate concentrations as low as 2 mM without affecting yield and nitrate accumulation in leaves. Since, the nitrite content was higher in plants grown in the 2 mM nutrient solution compared with 10 or 20 mM, for cultivation purpose a nutrient solution containing 10 mM can be suggested.

References Trivellini, A., Ferrante, A., Vernieri, P. and Serra, G. 2011. Effects of promoters and inhibitors of ABA and ethylene on flower senescence of Hibiscus rosa-sinensis L.”, J Plant Growth Regul. 30, 175-184.

Cataldo, D.A., Haroon, M., Sehrader, L.E. and Youngs, V.L. 1975. Rapid colorimetric determination of nitrate in plant tissue by titration of salicylic acid, Commun Soil Sci. Plant. Anal. 6, 71-80.

Nitrogen Workshop 2012

Reducing Nitrogen in a High-Input Chinese Double-Cropping System – Effects on Yield, Soil Nitrogen and Mineralisation Hartmann, T.a, Schulz, Ra, Müller, T.a, Chen, X.P.b, Zhang, F.S. b a Plant Nutrition and Soil Matter Dynamics, Department of Crop Science, Universität Hohenheim, Stuttgart, Germany b College of Resources and Environmental Sciences, China Agriculural University, Beijing, PR China

1. Background & Objectives The People's Republic of China (PRC) faces two major issues, which may or may not be antagonistic to one another. On the one hand, the Government must ensure food security for an ever growing population; on the other hand, it must find a way to reduce environmental pollution, a large portion of which is caused by agricultural production systems. In the North China Plain, the PRC's most important area for the cultivation of wheat and maize, the use of synthetic nitrogen fertilisers has continuously increased, while grain yields have remained stagnant or decreased for the last twenty years (China Agricultural Yearbook, 2008). In a winter-wheat / summer-maize double cropping system, up to 600 kg of nitrogen are fertilised per year per hectare, resulting in a continuous excess of nitrogen accumulating in the soil profile, which leads to nitrate leaching (Subbarao, 2006), and the emission of climate relevant trace gases (Yan, 2003). The described experiment evaluated alternatives to the current fertilisation system, with the aim of reducing nitrogen input while retaining current yield levels of a winter-wheat / summer-maize double cropping system, thereby reducing N surpluses, and subsequently the risk of nitrogen losses.

2. Materials & Methods In a field experiment carried out from May 2009 to October 2011 in Quzhou, Hebei Province, PRC, 8 nitrogen treatments were compared in a winter-wheat / summer-maize double cropping system, in order to observe effects on yield and mineral nitrogen contents in the soil. Chosen treatments of this experiment are the two control treatments C (Control): 0 N; FP (Farmers' practice, urea): 550 kg N ha-1 a-1, R (Reduced, urea) and ASN+NI (Reduced, ammonium sulphate nitrate + nitrification inhibitor DMPP).The reduced treatments were fertilised according to nitrogen demands of the crop and taking mineral nitrogen in the soil (Nmin, 0-90 cm depth) into account. The fertilisation rates of the reduced treatments were determined individually.

Apparent Nitrogen Use Efficiency (NUE) of the fertilised treatments was determined using the

following formula:

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The content of mineral nitrogen in the soil profile was determined throughout the experimental period, in order to observe possible reductions of mineral nitrogen over time.

3. Results & Discussion The experiment showed that nitrogen fertilisation in a Chinese wheat / maize double cropping system can be reduced by up to 50% compared to farmers practice (FP), without significantly affecting the yield of either maize or wheat. A significant reduction in yield could only be observed in the zero nitrogen control treatment (C) of wheat in both years, and in the third year of maize cultivation (data not included).

Nitrogen Workshop 2012

Nmin concentrations in the soil profile (0 – 200 cm) of the zero control treatment decreased in the first year (C), while the reduced nitrogen treatment (R) showed a stable or slightly reduced Nmin content, and nitrogen continued to accumulate in the profile of the FP treatment.

–  –  –

Despite low Nmin concentrations in the soil of treatment C, the zero control treatment showed no significant reduction of yield compared to fertilised treatments in the first two harvests of maize, which indicates that, taking the deposition of atmospheric nitrogen into account (approx. 80 kg N ha-1 a-1), there must be a strong mineralisation of organic nitrogen or release of adsorbed ammonium in the soil during the summer vegetation period, which is characterised by both high temperatures and precipitation.

4. Conclusion A reduction of fertilisation rates drastically reduced the amount of nitrogen in the system, while ensuring a retention of the current yield levels in this experiment. Reducing the amount of nitrogen in a system is the first step towards reducing the loss of nitrogen through emissions and leaching.

Further research should determine total nitrogen fractions in soils, including exchangeable and fixed nitrogen in order to understand nitrogen dynamics in overloaded agricultural systems.

References China Agricultural Yearbook (2008), China Agriculture Press Yan Xiaoyuan. 2003. Estimation of nitrous oxide, nitric oxide,and amonia emmissions fro croplands in Eas, Southeast and South Asia, Global Change Biology 9, 7 Subbarao., G.V. 2006. Scope and strategies for regulation of nitrification in agricultural systems – challenges and opportunities, Critical Reviews in Plant Sciences 24, 4

Nitrogen Workshop 2012

Soilless cultivation of vegetables in The Netherlands to reduce nitrogen emissions de Haan, J.J.a, van Os, E.A.b, Blind, M.Pc., Verhoeven, J.T.W.a a Applied Plant Research Wageningen UR, P.O. Box 430, 8200 AK Lelystad, The Netherlands b Plant Research International Wageningen UR, P.O. Box 16, 6700 AA Wageningen, The Netherlands c Proeftuin Zwaagdijk, Tolweg 13, 1681 ND Zwaagdijk-Oost, The Netherlands

1. Background & Objectives Many vegetable crops in open field production in The Netherlands do not meet the requirements of the European Union (EU) Water Framework Directive and EU Nitrates Directive mainly because of high nitrate emissions. In addition, these cropping systems have difficulty in complying with new market requirements, such as pesticide residues and constant quality and delivery. Within the current cropping systems, there are few options available to reduce these emissions without affecting the crop productivity and crop quality (de Haan et al., 2010, de Haan et al., 2009). The objective of this paper is to describe the development of soilless, recirculating profitable cropping systems for leafy vegetables and cabbages to reduce nitrogen emissions and to comply with other demands.

2. Materials & Methods A structured method was used to design and develop new cropping systems derived from other methods used in the design of open field production systems (de Haan and Garcia Diaz, 2002;

Vereijken, 1997), protected cultivation systems (van Henten et al., 2006) and animal husbandry systems (Groot Koerkamp and Bos, 2008). The systems focussed on iceberg lettuce (Lactuca sativa var. capitata), lollo rosso (Lactuca Sativa var. acephala), leek (Allium porrum) and cauliflower (Brassica oleracea convar. botrytis var. botrytis). First, an analysis was made of the current cropping systems of leafy vegetables and cabbages taking into account technical as well as environmental, societal and legal aspects. Secondly, a summary of requirements was established for all crops and various systems were designed, engineered and tested in the first year on a small scale on experimental farms. The systems which fulfilled the requirements were selected for further development. This process was repeated once more to select the most promising system for a crop.

This final system was further optimized e.g. fertilization, variety use and growing media and laid out on a larger scale, preferably with a commercial grower. The sustainability and profitability of

the selected systems were assessed in detail on all sustainability aspects (Planet, People, Profit):

Planet aspects considered nutrient and pesticide emissions, energy use, climate change, land use, water, biodiversity and waste; People aspects considered labour and food quality and Profit aspects considered profitability, financial risks and competitiveness.

3. Results & Discussion Results showed that all crops could be grown on various chosen soilless systems. For all vegetable crops, recirculating deep flow systems are increasing and show potential to fulfil the set requirements. Main advantages of deep flow systems are minimal use of substrate, robustness because of a large buffer due to the water volume as well as good fertilization and temperature control.

Production per hectare per year was much higher compared to field production. For instance, leek production was much higher on deep flow systems with 200-300 ton leek ha-1 year-1 in four cropping periods with much higher planting densities (70-80 plants m-2), compared to field Nitrogen Workshop 2012 production with 30-50 ton ha-1 in one cropping period with planting density of about 16-20 plants m-2.

Crop production was much steadier compared to field production with a constant growth rate irrespective of dry or wet periods, less loss of plants, cleaner products without soil or organic contamination and less damage and loss of quality due to pests and diseases. In addition, there are no problems with accessibility of land in wet periods during planting, harvesting or crop treatments.

Recirculation of water on an experimental scale gave no problems with pests and diseases. In leafy vegetables, water was reused during two growing seasons without any adverse effect on crop production. However, there will be discharge of water from the systems because of accumulation of salts or precipitation deficits as the systems are not covered. Current investigations are underway to study the best way of minimizing nutrient emissions to surface- and groundwater from these systems and to conduct sustainability assessments. Implementation of the systems has already started as some leading vegetable growers have started their own experiments.

4. Conclusion Soilless cultivation of open field vegetables is technically feasible and expected to be profitable. It gives new possibilities for farmers to grow better products for new market sectors with higher yields. Soilless cultivation has the potential to reduce nitrate emissions drastically. However, how much reduction is possible with these recirculation systems is still under investigation.

References de Haan, J.J., Zwart, K.B., Smit A.B. and van Geel W.C.A. 2009. Can intensive arable farming systems on sandy soils in the Netherlands meet the targets in the nitrate directive? Proceedings 16th Nitrogen Workshop, Connecting different scales of nitrogen use in agriculture, Turin, Italy, 28 June – 1 July 2009, 471-472.

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