title / Desk study to evaluate the practical benefits and constraints of fertiliser placement
/ DEFRA
project code / NT2504
Department for Environment, Food and Rural Affairs CSG 15
Research and Development
Final Project Report
(Not to be used for LINK projects)
Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports Unit
DEFRA, Area 301
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Project title / Desk study to evaluate the practical benefits and constraints of fertiliser placement
DEFRA project code / NT2504
Contractor organisation and location / Horticulture Research International
Wellesbourne
Warwick CV35 9EF
Total DEFRA project costs / £ 21,948
Project start date / 01/12/01 / Project end date / 31/03/02
Executive summary (maximum 2 sides A4)
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CSG 15 (9/01) 2
Projecttitle / Desk study to evaluate the practical benefits and constraints of fertiliser placement
/ DEFRA
project code / NT2504
The farming and horticultural industries are under environmental and economic pressures to adopt fertiliser practices which minimise inputs and reduce losses to the environment. However, wide-spaced row crops are inefficient at recovering nutrients from conventional broadcast fertiliser applications spread uniformly over the soil surface, because of the limited ability of their roots to exploit the soil between the rows. To overcome this problem alternative fertiliser application techniques have been developed which target the supply of nutrients more accurately to crop roots.
The aim of this project was to summarise the potential effectiveness of these new placement techniques (e.g. banding, starter fertiliser, fertigation), to estimate their current level of use within key farming sectors (field vegetables, potatoes, sugar beet, forage maize, soft fruit and orchard fruit) and to identify any constraints to their further adoption.
Information on the agronomic and environmental benefits from placement, under UK conditions, was determined from the scientific literature. Use by the industry and the perceived benefits and constraints of the techniques were derived from detailed discussions with crop consultants, leading growers, fertiliser suppliers and equipment manufacturers.
From the literature survey it was evident that no one placement technique was best for all crops, nor one technique consistently superior to broadcasting under all conditions. Nevertheless yield benefits and scope for fertiliser reductions of 20-40% were frequently found if:
· residual soil nutrients were low to medium
· soil temperatures were low
· root systems were sparse and inefficient
· plants were widely-spaced and had a short growing season
· other nutrients and water were non-limiting
Awareness of most placement techniques amongst farmers and their consultants was exceptionally good, leading to a high level of adoption with many crops where they considered they were appropriate, for example:
· banding – 50% of maincrop potatoes, 90% of forage maize
· starter fertiliser – 50% of bulb and salad onions, 90% of early transplanted lettuce
· fertigation – 80% of strawberries, 50% of runner beans
The main reason given for using these techniques was the benefit arising from improvements in early growth due to the greater spatial availability of nutrients and from the more accurate distribution of fertiliser, compared to broadcasting. These lead to improved crop uniformity, greater flexibility in timing of herbicide applications, earlier maturity and often higher marketable yields. A secondary consideration is that improved accuracy of application also avoids fertiliser wastage in wheelings and other uncropped areas of the field. A lack of consistent benefit with sugar beet grown in the UK means that use of fertiliser placement is negligible, which contrasts to the situation in some north European countries.
Early placement research was aimed at increasing crop yields. It is only recently that the potential for placement to improve nutrient use efficiency and minimise losses to the environment has been considered. These potential benefits have been largely inferred in the literature from observations that yields can be maintained with less fertiliser, as there is a paucity of direct evidence that residual soil nutrients are lower at harvest.
The potential for reducing fertiliser inputs to minimise the environmental impact of fertilisers is not yet a driving factor in the uptake of fertiliser placement. While the majority of farmers reduce base applications to compensate for placed nutrients, opportunity is rarely taken to reduce overall application rates in line with recent research results. This is attributable to the lack of incentive for growers to do so (although this may change with expansion of NVZs) and the perceived risk of reduced yields and quality from under-fertilising their crops. At present guidelines on placement contained in RB209 are not sufficiently detailed to enable farmers to reduce nutrient levels with confidence. The latest research findings will only be adopted by the industry if the techniques are adequately verified, demonstrated and promoted.
SUMMARY
· Farmers, growers and crop consultants are aware of most placement techniques.
· Use of the appropriate placement technique for various row crops is high.
· Use of placement is highest where there are obvious improvements in early growth and marketable yield (forage maize, Alliums, lettuce), or there are specilised requirements (soft fruit).
· Increased use with some crops (sugar beet, potato) or of some techniques (fertigation, point injection) would require clear establishment of benefits under UK conditions.
· There is some concern at the capital cost of placement machinery.
· Placement minimises wastage of fertiliser in uncropped areas of the field (eg wheelings), potentially reducing losses to the environment.
· Few attempts are made to benefit from improved efficiency of nutrient uptake by reducing overall fertiliser rates.
· More specific advice and field demonstrations are needed, particularly of in-row banding and starter fertiliser, if growers are to use these techniques to reduce fertiliser rates.
· Fertigation has potential and is receiving interest for some crops (runner bean, lettuce, celery, potato) but more information is needed on scheduling of nutrients.
· The risk of increased residual soil P levels from regular use of banded high P fertilisers in combination with animal manures (forage maize) needs to be evaluated.
CSG 15 (9/01) 2
Projecttitle / Desk study to evaluate the practical benefits and constraints of fertiliser placement
/ DEFRA
project code / NT2504
Scientific report (maximum 20 sides A4)
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CSG 15 (9/01) 2
Projecttitle / Desk study to evaluate the practical benefits and constraints of fertiliser placement
/ MAFF
project code / NT2504
INTRODUCTION
Reducing profit margins and increasing environmental concerns about high levels of nitrate in ground water and nitrate and phosphate in surface waters is creating pressure on the farming industry to adopt more nutrient-efficient practices. In order to meet EU legislation on nutrient pollution, techniques are sought which reduce losses of nitrogen (N) and phosphorus (P) to the environment through leaching, erosion and surface run-off. This has prompted DEFRA and the farming and horticultural industries to fund research into new methods for optimising inputs of nutrients and their utilisation by crops. Such research has led to the development of improved fertiliser recommendation systems, which reduce the risk of over-fertilisation by improving the match between nutrient supply and crop demand (Bradbury et al. 1993, Greenwood et al. 1996, MAFF 2000). Farmers and growers are now encouraged to follow these recommendations as part of Good Agricultural Practice in order to reduce nutrient residues remaining in the soil at harvest (MAFF 1998).
Conventional fertiliser practice for many arable and vegetable crops is still, however, based largely on broadcast applications of granular materials, which are spread uniformly across the soil surface. Measurements show that the recovery of nutrients from these applications is often low (for example 10% N recovery for lettuce), even when applied at the optimum or recommended rate (Greenwood et al. 1989). Wide-row crops, in particular, can be quite inefficient at recovering nutrients because of their limited ability to effectively exploit the soil between the rows. As a consequence, large residues of unused nutrients can remain in the soil at harvest, which are at risk of loss to the environment during the winter. For example, this has been identified as an important contributory factor in the large accumulation of nitrate residues in the subsoil after intensive brassica cropping (Rahn et al. 1992).
During the early stages of growth, the roots of annual crops are able to exploit only a small volume of soil from which they must absorb sufficient nutrients to meet their demands (Costigan 1987). If this demand is not met, the crop can suffer a transient nutrient deficiency, which may irreversibly depress final yield (Burns 1990, 1996). To compensate for poor uptake during the establishment phase, recommended rates of broadcast fertilisers are often high and this can lead to over-fertilisation later in growth. Effective fertilisation of crops therefore requires that sufficient nutrients are added to the soil to provide:
· the concentrations of nutrients needed to sustain uptake during seedling growth while their root systems are developing
· the quantities of nutrients needed to sustain uptake during the ‘grand period’ of growth when dry matter production is at its greatest.
Failure to optimise the nutrient supplies at either of these two stages of growth will reduce the overall efficiency of fertiliser use and may affect the production efficiency of the crop.
In an attempt to meet these requirements, several fertiliser application techniques have been developed, which target the nutrient supply more precisely, both spatially and temporally, to the roots of widely spaced crops, e.g. side-banding, starter fertiliser and fertigation. Results show that these can significantly increase the recovery of N and/or P for many of these crops, potentially reducing the environmental impacts of the fertiliser, without compromising yield or quality of the produce (Stone 2000a). Recent reviews have advocated using these techniques as a component in modern fertiliser management strategies (Neeteson et al. 1999, Sanchez & Doerge 1999, Rahn 2002), but it is unclear to what extent they have been adopted by farmers and growers.
The purpose of this project was to summarise the potential agronomic and environmental effectiveness of these new fertiliser placement techniques for N and P, to estimate their current level of use within key farming and horticultural sectors and to identify any constraints to their further take-up by the industry.
METHODOLGY
Fertiliser application methods
The definitions of the application methods included in this report and their basic merits and drawbacks are given below:
Broadcast. An application of fertiliser applied evenly over the field surface and frequently incorporated into the topsoil or seedbed by cultivation. Broadcasting is a relatively speedy operation with fertiliser spreaders covering a wide swath, although distribution is often lacking in precision. Another disadvantage of this method is the close contact between fertiliser granules and soil so that microbial transformation of ammonium-N to more easily leachable nitrate-N and fixation of P can be high.
Base application. A fertiliser dressing applied before the crop is planted.
Top dressing. A fertiliser application made over the top of the growing crop.
Banding. Application of granular or liquid fertiliser, in a narrow zone or band, parallel to the crop row, either beside the row (side banding, Cooke et al. 1956) or spanning the centre of the row (in-row banding, Paterson 1998). It may be applied to the soil surface before or after planting or, more usually, placed below seed depth. Banding offers a more controlled, but slower operation than broadcasting, with less wastage occurring in tractor wheelings and uncropped areas of the field. As the fertiliser is concentrated in a small volume of soil, lock-up by microorganisms or the soil is potentially less than for broadcasting.
Starter fertiliser. A low rate of fertiliser placed below but close to the seed or transplant at planting (Costigan 1988). Starter fertiliser, generally containing N or NP is often applied in addition to normal broadcast application rates to boost early growth (Costigan 1988) but it can also be used to supplement reduced rates of conventional applications (Stone 2000b). This early stimulation of crop growth is often termed “pop-up effect”, particularly in the USA (Anon 1999).
Fertigation. The application of fertiliser in irrigation water using a drip or trickle system (Elfing 1982, Haynes 1985). It enables precise application of nutrients to be made to the crop root zone and improved timing of applications, which enables nutrient supply to be tailored to crop demand throughout growth.
Fertiliser depots. In this technique a urea or ammonium-based fertiliser pellet (10-30 mm diameter) is incorporated close to the crop row at planting to provide N for the entire growth period of the crop (Sommer 1993). The high ammonium concentration in a localised soil area inhibits microbial activity, minimising nitrification and subsequent losses by leaching (Sommer et al. 1987).
Point injection. Similar in principle to depots, this is the application of a discrete pulse of liquid fertiliser at around 60 mm depth and 175 mm intervals alongside the crop row using a spoke-wheel injector (Baker et al. 1989), or crank operated probe (Womac et al. 1990). It may be used close to planting time or, with minimal root disturbance, later during crop growth.
Literature search
A search of the scientific literature using the CAB Abstracts and ISI Web of Science electronic databases, covering the years from 1973 and 1981 to 2001 respectively, was made in order to provide quantitative data on the agronomic and environmental benefits of various fertiliser placement techniques. The extracted papers were filtered to include only those applicable to the wide-row crops of field vegetables, maize, potato, sugar beet, orchard fruit and soft fruit, grown under UK or north European conditions or equivalent, and were further restricted to those where comparisons had been made with conventional applications. This gave a total of 188 papers, see Table 1. In addition, key papers predating the electronic abstracts were also consulted, if considered relevant.