Download HL0165 – Improved efficiency of nutrient and water use for high

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
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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.