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HL0165 – Improved efficiency of nutrient and water use for high quality field vegetable production using dynamic fertigation: PINT (Precision irrigation & Nutrient uptake) Aim of Initiative To increase efficiency of inputs in the production of perishable field vegetable crops, reduce wastage in the retail sector, and in line with impending regulatory pressures, to provide an integrated framework for the precise scheduling and delivery of water and nutrients to the root zone to manage crop quality, marketable yield and shelf-life. This will be driven by developing an understanding of the influence of nutrient supply during development on crop quality, and the physical principles governing the precise application of water and nutrients in a sustainable way. Commercial and Technical Background Increasingly, the retailer has to provide quality guarantees for perishable produce to the consumer, who needs assurance that the fresh vegetables he buys is produced in a safe and environmentally-sustainable system. The retailer needs to compete on price and this can only be achieved through efficient management of the retail supply chain to optimise quality at each stage, whilst reducing material wastage and associated transport and packaging costs. Increased consumer demand for high quality fresh convenience produce is driving rapid market growth in the added value prepared salads and prepacked vegetable sectors. Fresh produce is highly perishable and significant wastage is seen throughout the chain, from producer to retailer and consumer. Techniques are needed that improve resource use efficiency in a way that enables effective management of raw material quality from the field to the consumer, whilst increasing supply chain efficiency to deliver good value to the consumer with minimal environmental impact. Conventional fertiliser applications do not necessarily ensure nutrient supply is optimised at all growth stages. Growers may fertilise as insurance against nutrient stress, tending to over-apply fertilisers, which when coupled with high water inputs (poor irrigation management or heavy rain) results in strong leaching to the environment. Under supra-optimal nutrient conditions, crops can accumulate 'luxury' amounts of the nutrient in their foliage resulting in elevated foliar nitrate levels. There is therefore an urgent need for more targeted fertiliser use, with greater efforts being devoted to developing efficient methods of nutrient management, particularly through using drip fertigation technology, which is far more efficient than conventionally-use overhead irrigation systems. Fertigation, the combination of irrigation and fertiliser application, offers opportunities for precision manipulation of nutrient supply during growth, whilst increasing the efficiency of water and nutrient application. Model systems need to be studied in order to provide the basis for extrapolation to a wide range of field vegetable crops. Salads and beans have been selected as the model crop species as they are both high value crops with expanding market potential. Both require intensive labour and resource inputs and both are grown in the country's nitrogen vulnerable zones (NVZs) and therefore need careful management to meet legislation relating to nutrient runoff. Salad crops represent a model short-season, vegetative leafy vegetable, whilst beans represent a longseason reproductive legume with marked phenological developmental stages. The UK field salad and bean growers have identified a need for sustainable systems for improving efficient application of water and nutrients in order to minimise leaching and pollution of water resources, whilst effectively managing marketable yield and quality at harvest and post-harvest. The industry wishes to exploit fertigation approaches to achieve this, but the scientific information for implementing the technology reliably under UK conditions needs developing. Novel drip irrigation software, developed for semi-arid regions, needs to be adapted for UK use. The use of drip irrigation offers the possibility of efficient, targeted application and manipulation of water and nutrients during crop development to a far greater extent than is possible using conventional solid fertilisers. This technology needs to integrate knowledge of nutrient manipulation with automated systems for monitoring and controlling soil moisture and conductivity, currently being developed by project consortium members, in order to increase efficiency and consistency of application. The Problem/Opportunity "The UK is a water scarce country and quality demands are increasing" (quote Jacob Tompkins, Policy Development Adviser, Water UK). The UK Draft Water Bill and EU Water Framework Directive puts increased legislative pressure on growers to improve water use efficiency, including the licencing of abstraction for trickle irrigation, with new EU legislation defining maximum nitrate levels in edible produce (3). The establishment of NVZs restricts the timing and seasonal levels of organic nitrogen application to a maximum of 210 kg/ha reducing to 170 kg/ha total N which must be limited to crop use (after 19/12/2002), with financial penalties of up to £20,000 for those prosecuted by the Environment Agency for consistent failure to comply. Efficient, accurate application of N to meet crop requirement is an essential part of conforming to the legislation. Most salad and bean producers will be located in flat, low-lying floodplains designated as NVZ areas. Investment in technologies that improve water and nutrient use efficiency will be essential to meet these legislative requirements. New developments in the areas of soil moisture and pore water conductivity measurement technology provide new opportunities for adapting and developing systems to deliver precise control of root zone moisture and nutrient supply with maximum efficiency. The proposed research offers improved timing, rate and spatial delivery of moisture and nutrients for optimising quality in the UK, but will need to be adapted and evaluated before it can be applied reliably to UK crops and situations. The ‘Bag Salad’ industry has enjoyed considerable growth in the last decade. It has achieved this largely through increased market penetration – more consumers / households purchasing the product. Market penetration is now estimated at around 64%. As the market for prepared salads matures (and penetration reaches it’s ceiling), further growth will be driven by increased ‘frequency of purchase’ and ‘weight of purchase’. One significant barrier to increasing these factors is the apparent shelf life of the product. It is known that 78% of purchases are consumed within 2 days – consumers (who shop weekly) are unable to buy salads reliably for consumption over the whole week. Consequently, extending the shelf life has the potential to significantly increase the number of units purchased at a time. Cut salad crops are prone to high wastage pre- and post-processing (30%) so that while recent annual market growth has been 15-20%, sustaining future expansion will depend upon improvements in production efficiency, crop quality and reduction of wastage in the field, factory and retail chain to encourage repeat purchase by the consumer. Runner beans suffer from high levels of flower and pod abortion, combined with up to 50% wastage at early harvests due to pod quality defects and although drip irrigation Increased pressure for quality assurance in the retail chain requires improved systems for batch quality control and produce management. The industry needs to evaluate techniques for objective quality measurement and prediction that can be developed as diagnostic instruments. Previous DEFRA and EU-funded research at HRI in hydroponic systems has shown that manipulation of N, P, K and Ca in beans and salads influences growth, development, yield (1) and post-processing quality (2), yet there is little understanding of the influence of nutrient supply on quality (and particularly postharvest quality) in soil-based systems. HortLINK and EU funded research at HRI (projects HortLink 232, EU FA-S2-CT98-9089) have demonstrated that the quality of field-grown processed salads can be influenced by nutrient supply, which is one of the few factors that growers can control. Scientific Background Pre-harvest factors influence quality: Although there is a body of research quantifying the effects of nutrition on yield of vegetable crops, only general qualitative relationships have been reported for the effects of nutrition on quality, with the interactions between nutrition and post-harvest quality remaining largely unexplored. HRI has considerable expertise in working with the industry to study the effects of pre-harvest factors on postharvest quality in a range of field and protected crops, and has developed robust nutrient supply models describing crop responses to N, P and K (4,5,6, 7 and on the WWW at www.qpais.co.uk/nable/nitrogen.htm, www.qpais.co.uk/phosmod/phos.htm, and www.qpais.co.uk/moda-dig/potass.htm respectively), and input data for RB 209 (MAFF UK Fertiliser recommendations). Applications of calcium reduce problems associated with lettuce tip-burn (8, 9), and internal breakdown in cabbage (HortLINK 15); the form of applied N impacts on lettuce nutritional quality (10) and manipulation of N:K ratio and calcium supply influence quality of processed salads (projects HortLink 232, EU FA-S2-CT98-9089). Non-destructive quality descriptors: HRI has developed considerable experience in collecting and modelling chlorophyll fluorescence data as part of Horticulture LINK project HL0134LPC (Robust product design and prediction for post-harvest pot-plant quality and longevity). This project used the rapid induction kinetics of chlorophyll fluorescence on pot-plants at the point of sale to predict the after-sales performance of the plants. Measurements were made on many occasions under controlled environmental conditions on similar leaf types, using both modulated and non-modulated fluorescence methods. The project found that the non-modulated spectral response curve for each plant could be summarised by a performance index measure and means of this index, within a batch of plants, could be used as a predictor of the future home-life performance of the batch. The performance index was supplied by the project consultant Professor Strasser at the University of Geneva as a theory-based measure of photosynthetic activity calculated from the measured fluorescence parameters. This approach was extended and generalised in DEFRA project HH1530SPC (Chlorophyll fluorescence spectral discrimination by artificial neural network methods) which dropped the assumption that the theory-based performance index at the point-of-sale should necessarily be the best predictor of plant home-life performance. Instead, the project Field experiments will be designed to test the hypothesis that, compared to conventional fertiliser practice, controlling timing and supply of N, P and Ca to lettuce, and N, K and Ca to beans, using liquid fertigation techniques will improve the efficiency of water and nutrient supply, whilst influencing marketable yield and quality at harvest and post-harvest. N, P and K nutrient supply models will inform treatments. Plant growth and plant and soil mineral analysis data, collected during the experiments, will be used to validate model performance under field conditions. Nutrient leaching under different experimental treatments and in different soils will be quantified using measurements of mineral N. This will provide basic data for ameliorating nutrient losses from cropped systems into the environment under different irrigation and fertiliser systems. For each crop, interrelationships will be established between the supply of key nutrients, foliar mineral composition at key developmental stages, and objective measures of quality at and post-harvest. Following on from work on ornamental plants in HortLINK 194 (Robust Product Design), the potential for using non-modulated chlorophyll fluorescence measurements as quality "predictors", rather than as "descriptors" will be evaluated for vegetables. Measurements will include, those collected during rapid induction kinetics of fluorescence in dark-adapted leaves following excitation with a saturating light pulse, F0, Fv and Fm. The data will inform further detailed research in new projects designed to investigate specific mechanisms for the effects of nutrition on quality and for the potential of nondestructive quality predictors. Present irrigation technology relies upon a 'fill/refill' approach to soil moisture management. The ability to monitor and control irrigation/fertigation infiltration rates will deliver benefits both in terms of crop quality and water/chemical use. The research will utilise the HYDRUS-2D model to describe infiltration of moisture and solutes from overhead and drip line sources. The model will be parameterised for-, and moisture and infiltration patterns defined and validated, in a range of UK soil types represented at grower sites in the Consortium. The core programme of the HYDRUS-2D model will be used to optimise irrigation system layout on the defined soils, and together with new sensor technology, developed by Delta-T, for measuring moisture content and soil pore conductivity, a novel closedloop irrigation control system will be developed. Wetting patterns and solute movement, simulated using HYDRUS-2D, will be validated under field conditions. This will enable accurate, dynamic and potentially automated placement of water and nutrients into a 'pre-defined' rooting zone in the soil profile under field conditions. The system will comprise soil moisture and pore water conductivity probes linked to a sophisticated control system capable of interfacing into existing irrigation technology. The overall system will deliver: Research will be conducted to develop and evaluate a novel integrated framework for optimising approaches to manipulate water and nutrient supplies to two model crops: a model salad and a model legume crop. This will include: - Parameterising and validating HYDRUS-2D to provide a system for designing fertigation systems for UK soil and weather conditions. - Scenario testing. - Devising systems for exploiting the use of soil-based sensors for scheduling water and nutrient supplies. - Promoting the results to the industry through appropriate forums. - Evaluating the potential for non-destructive techniques as quality predictors. The proposed research will: (i) optimise the efficiency of delivery and utilisation of water and nutrients in the root zone for Green Batavia - a model salad and Runner Bean - a model legume crop; (ii) identify and quantify the interactions between nutrient supply and quality, at harvest and post-harvest; (iii) result in development of a new soil sensor combined with soil infiltration models, to give closed-loop feedback irrigation control; (iv) evaluate the potential for quality assessment and prediction of quality using colorimetry and chlorophyll fluorescence. The project will deliver improved protocols for efficient application of irrigation and nutrients for quality management in field vegetable crops. It will improve the efficiency of the whole supply chain, reduce material wastage and form the basis for development of an integrated framework for precise delivery of water and nutrients to the root zone appropriate to environmental conditions and the stage of crop development.