Importance of Traceability

Consumers the world over are increasingly wanting to know the food they are eating is safe. This particularly the case in the discerning markets NZ’s high quality food products are sold. They also want to know that the environment is not being harmed by the farming practices being used.

In July 2006 Minister of Agriculture Jim Anderton confirmed the importance of on-farm traceability. He said, "Society is raising the environmental standards for land users and is voicing concern about the water quality in our rivers and lakes. At the same time farmers are increasing the use of fertiliser and nitrogen on hill country to achieve greater productivity. …

The way of the future will require fertiliser to be applied more accurately to meet the precise nutrient needs of a particular crop or farming system. Increasingly on-farm quality assurance schemes are driven by the consumers’ desire to be reassured that the food that they eat is safe and free from harmful contaminants. This is driving traceability schemes where the farmer is required to be able to say that all on-farm practices are carried out to a standard that ensures total safety of the food product.”

The fact is, that whether we like it or not, society, and our customers, are expecting farmers to operate to higher environmental standards than in the past. TracMap has been designed to make it easy to deliver on those expectations.

Some links to examples of news articles and websites on this topic

Farmers Fined for Pollution - ODT 29 Apr 2008
Eyes on Taupo - Rural News - 21 April 2008
Future Focus - Signposts to Success for NZ Agriculture Industries
MAF's strategic foresight project in 2007 identified six key global drivers of change over the next 20 years, and the strategic risks and opportunities arising for New Zealand's agriculture, food and forestry sectors, and in the biosecurity setting - MAF Website
 
Land Based Industries Sustainable Future -Speech by Jim Anderton - 20 Sept 2007
Minister of Agriculture Jim Anderton explaining the TracMap system to the Uruguayan Minister of Agriculture at the Royal show in Nov 2007.
The following part of our site is in early stage of development, and in time will be better indexed and structured.
 
 

TracMap has commissioned research into finding examples of science research into the value of achieving accurate fertiliser spread in terms of

  • Improvement in farm productivity and profitability
  • Reduction in environmental impact from Nitrous Oxide release, and nutrient impact on groundwater.
Some of these papers are listed below.
Executive Summary
Much of the research to date has focused on the use of precision agriculture for planting crops, fertiliser placement (banding), yield mapping and soils variability. Most of the research has also tended to be in high value crops (cotton, soybean, cereal, maize) rather than pastures. These large cropping systems common to the USA and Australia could justify the high cost of precision systems (early adoption of technology is always at a premium). Research is just beginning to move in to efficiency modeling for fertiliser and water.
As environmental constraints and traceability become greater issues in both growing and marketing agricultural product then we can expect both more adoption of precision technology including GPS and more aligned research.
There is very little information directly related to the environmental advantages of improved fertiliser placement. Strategic N use research has focused on economic rates to apply which has depended strongly on the economics of the farming system being considered at the time, eg. sheep, beef or dairying. The research priority from an environmental view has been focused on reducing the impact from the animal and from effluent spreading.
Fertiliser N use has increased considerably over the last few years especially on dairy farms, and now 100kgN/ha is common and more intensive farms using up to 400kgN/ha/year. Leaching losses increase significantly above 200kgN/ha compounded by high stocking rates. This is because most of the leaching is still related to the urine deposition rather than the fertiliser use.
Strategic N use reduces the risk of nitrate leaching from applied fertiliser (or effluent). The recommendations (NZ – Roberts et al. 1992, Proc. of Ruakura Dairy Farmers Conference) are to apply at rates between 30-40kgN/ha per application and less than 200kgN/ha/yr.
The information is presented in three ways
  • website accessed material
  • full papers attached
  • relevant info distilled from research - some of this is easily available only as abstracts
The following websites provide some summary information on where NZ farming and research is at.
www.maf.govt.nz/mafnet/rural-nz/sustainable-resource-use/resource-management/groundwater-nitrate/httoc.htm (Implications of Groundwater Nitrate Standards for Agricultural Management) - a synopsis of studies by enterprise. This is a good summary of where our research is to date and some of the assumptions made for the economic impact of changing practice (with current knowledge and technology)
Massey University presentation on precision ag. and efficient fertiliser spreading – improved nutrient management
http://digitalearth06.org.nz Carolyn Hedley, Landcare Research, NZ Precision Agriculture – digital technology for improved sustainable farming (powerpoint summary)
http://www.landcareresearch.co.nz/news/docs/Tools_Workshop_Programme_Abstracts.pdf: Precision Agriculture tools for sustainable soil and land management, Landcare (there doesn’t appear to be full proceedings published so only the abstracts are available)
Some of the following papers are available to download as PDF files from our website. Others are only in hard copy format. Please contact our office if you would like copies of any posted to you.
1. Optimising fertiliser use on the dairy farm
D.C EDMEADES and G BRIER, 2006 - www.side.org.nz
B THORROLD, DEXCEL - www.side.org.nz
3. Using Nitrogen: what is best practice?
K CAMERON, H.J. DI, J. MOIR, R CHRISTIE, R PELLOW, 2005- www.side.org.nz
4. Improving your business using nutrient budgeting
M. BRAMLEY, F. PORTEGYS, I. TARBOTTOM, 2005 -www.side.org.nz
  1. Dairy farming, nitrogen losses and nitrate-sensitive areas
S.F. LEDGARD1, C.A.M. DE KLEIN2, J.R. CRUSH1 AND B.S. THORROLD1, Proceedings of the New Zealand Society of Animal Production 60: 256-260
  1. Nitrogen inputs and losses from clover/grass pastures grazed by dairy cows, as affected by nitrogen fertilizer application
S. F. LEDGARD, J.W. PENNOand M. S. SPROSEN, Journal of Agricultural Science, Cambridge (1999), 132, 215-225.
  1. Nitrogen responses on pastures in the southern South Island of New Zealand
L.C. SMITH1, J.D. MORTON2, W.D. CATTO3 and K.D. TRAINOR,Proceedings of the New Zealand Grassland Association 62: 19–23 (2000)
  1. Pasture response to fertiliser inputs under dairy grazing
J.S. ROWARTH’, C.G. PENNELL, T.J. FRASER and D.B. BAIRD,Proceedings of the New Zealand Grassland Association 58: 123-127 (1996)
  1. Fertiliser evenness – losses and costs: A study on the economic benefits of
uniform applications of fertiliser
R. HORRELL1, A.K. METHERELL2, S. FORD3 and C. DOSCHER4Proceedings of the New Zealand Grassland Association 61: 215–220 (1999)
  1. A desktop evaluation of the environmental and economic performance of model dairy farming systems within four New Zealand catchments
R.M. MONAGHAN, D. SMEATON, M.G. HYSLOP, D.R. STEVENS, C.A.M. DE KLEIN, L.C. SMITH, J.J. DREWERY, AND B.S. THORROLD, Proceedings of the New Zealand Grassland Association 66: 57-67 (2004)
  1. Environmental impacts of nitrogen in pastoral agriculture
R.A. CARRAN, AND T. CLOUGH, Agronomy Society of New Zealand Special Publication No. 11 / Grassland Research and Practice Series No. 6
  1. Estimation of the in-field variation in fertiliser application
H.G. LAWRENCE AND I.J. YULE, New Zealand Journal of Agricultural Research, 2007, Vol 50: 25-32
  1. Developing variable rate application technology: scenario development and agronomic evaluation
R.I. MURRAY and I.J. YULE, New Zealand Journal of Agricultural Research, 2007, Vol 50: 53-63
  1. Developing variable rate application technology: economic impact for farm owners and topdressing operators.
R.I. MURRAY and I.J. YULE, New Zealand Journal of Agricultural Research, 2007, Vol 50: 65-72
  1. Comparison of fertiliser strategies for reducing nitrate leaching from grazed grassland, with particular reference to the contribution from urine patches
S.P.CUTTLE, R.V. SCURLOCK, B.M.S. DAVIES, Journal of Agricultural Science, Cambridge, 2001, 136: 221-230
  1. Optimizing Organic fertiliser applications under steady-state conditions

D. M. CROHN, Journal of Environmental Quality, 2006, 35: 658-669

Summary of related abstracts
PRECISION AGRICULTURE IN AUSTRALASIA
2001 Symposium on Australasian Research & Application
Opportunities for Increased Profitability from Precision Agriculture
M.D. Craighead & Ian J. Yule
Ravensdown Fertiliser Co-operative/ New Zealand Centre for Precision Agriculture
A three year study using three sites in Canterbury New Zealand has shown that there is financial (and environmental) advantage in adopting site specific farming methods. Most of this benefit is derived from managing the crop in a way that is sympathetic to the variation in the paddock, variation such as soil depth and moisture retention.
This means varying the timings of nitrogen applications as well as the rate and protecting this investment with appropriate plant protection measures. The work has also highlighted 'at risk' areas of the crop as far as disease, invasive weeds and nitrate leaching is concerned.
Greater effort needs to be devoted to helping growers derive crop management strategies which go beyond the concept of simply varying rates of fertilisers or other chemical inputs at the time of application.
Precision Agriculture in Australian Cotton 2001
Broughton Boydell, Craig Stewart & Alex B. McBratney
Australian Centre for Precision Agriculture, University of Sydney
The accuracy of proximal cotton yield monitors was evaluated along with their operational reliability with results indicating a error of +-3% on a spatial scale of 6m x 6m is typical. Yield estimates derived from imagery collected with satellite based sensors (Landsat-7+ETM) was compared to proximally sensed yield measurements with results indicating that satellite imagery is capable of identifying the relative yield variability within fields.
Consecutive yield maps over 11 years were compared for three fields and analysed to determine whether the yield zones (relatively higher and relatively lower areas) were stable from year to year. Results indicate that for cotton fields which are typically irrigated, yield estimates from 3-5 irrigated years will produce a good map indicating the relative yield expected within a field. These stable regions may then be used as a basis for potential management zones.
Where the field is occasionally managed without the addition of irrigation, dryland management zones must be created using only previous years which were also managed without irrigation. Managing for yield variability within single cotton fields was examined by implementing fertiliser strategies aimed at applying nitrogen according to local requirement. Results to date showed no yield improvement but increased fertiliser efficiency use by employing the variable-rate strategies. These results were due mainly to the inadequacy of the current fertiliser recommendations for predicting site-specific requirement. At both sites, fertiliser rates were much too high.
Encouragingly, the management zone approach was very successful at dividing the field up based on yield potential. Once fertiliser recommendations specific to a management zone have been developed, the benefits of a variable-rate approach should be forthcoming.
Interdisciplinary Research for Precision Agriculture Preagro: the German Joint Project for an Integrated Management System
Thomas Selige, Armin Werner, Thomas Muhr & Urs Schmidhalter
Technical University of Munich
Since January 1999, site-specific crop production has been studied throughout Germany in a BMBF-funded joint research project, "Management system for precision agriculture to increase the efficiency of farming and promote its environmental compatibility". The central goal is to exploit the arable land more economically according to the principles of good agricultural practice and at the same time to cultivate it in a more environmentally responsible manner.
With 22 sub-programs operated by 13 research institutions, 2 service companies, 2 software companies and 16 farms, Preagro (www.preagro.de) is developing the base for decision support systems for crop management in precision agriculture.
At eight regions across Germany, the available and necessary data are analysed for their possibility to be used in determining the appropriate cropping measurements for sub-units within fields. Algorithms and rules for this crop management are developed and will be provided as software modules to be implemented in any farm software for precision
agriculture. Different methods to identify and describe conditions of site or crop stand are compared. New methods in soil survey, remote sensing or optical sensor systems at the fertiliser spreader are developed or tested. The algorithms and rules to manage the crop site-specifically are derived from agronomic knowledge and actual experiments.
The rules are developed for managing crops spatially variable with soil tillage (chisel ploughing), sowing density, fertilisation (N, P, K, lime), growth regulators and herbicides. Prototypes of the algorithms are applied on the test farms and will be validated for accuracy as well as the economical and ecological effects. The economical effects of managing crops site-specifically are determined especially for winter wheat and compared with adjacent fields which are managed uniformly.
The impact of site-specific management onto vertical and regional flow of nitrate in the soil is also studied. The opportunities to adopt environmental requirements to site-specific crop management are analysed for local objectives of nature conservation. The way to integrate these tasks is a cross-program linking multi-disciplinary research with industry and stakeholders from the public and the private sector (as farm managers, local governmental agencies, consulting companies, mechanical and software engineers) towards an interdisciplinary and comprehensive outcome.
Precision Management of Fertiliser Application to Pasture
Allan G. Gillingham, AgResearch
On most pastoral farms in New Zealand, fertiliser is the single largest expenditure item in the annual budget. Means of improving the efficiency of return from fertiliser use is of constant concern, however on most farms common fertiliser forms and rates are generally applied over the whole property or large blocks. Variability in pasture productivity and associated soil and plant characteristics occurs on all farms.
To date this has usually been recognised as being present but ignored as being relatively unimportant, or unable to be differentially managed. The advent of precision agriculture technology has produced two advances. The first is the ability to precisely identify and map small-scale variability, and the second is the development of variable rate fertiliser application technology. The challenge now is how to use these advances to improve on-farm economics.
The optimum differential application of fertiliser to pasture will require a more sophisticated basis for recommendation than has sufficed to date. Most models use generalised response curves derived over a number of contrasting seasons, and or from a number of sites with contrasting growth potentials. Such response curves are inadequate to fully exploit the potential from differential fertiliser application to contrasting growth zones. New models should be developed which incorporate the growth potential, together with the associated economic analysis, into the fertiliser recommendation for contrasting sites. From the results to date there appear to be worthwhile opportunities for adoption of PA approaches into pastoral farming.
Geospatial Information & Agriculture 2001
Precision Ag. – Oz style
A.B. McBratney1,2 and Brett Whelan1
Abstract
Precision Ag practitioners continue their pursuit of precision through "turning data into decisions." Economic studies are now beginning to show advantages of precision management. Precision agriculture terms are defined for Australia and elsewhere. We discuss a model for precision agriculture and review the management zone concept for site-specific crop management. The key areas of research for obtaining data layers and linkages, some of which is world-leading, are reviewed briefly. The principal industries involved are those cropping industries of highest value where yield monitors have become available, i.e., grains, cotton, sugar, viticulture and horticulture. Commercial activities include the provision of hardware for information gathering, software for information management and data generation and information management services. The future of precision agriculture in Australia requires the plugging of knowledge gaps, the development of new areas such as precision organic farming, and most importantly vigorous promotion and investment. The application of geospatial information technology to agriculture through precision agriculture is profitable, can create jobs in the bush, is environmentally friendly, and can give consumers a deserved confidence in the production process.
Fertiliser evenness – losses and costs: A study on the economic benefits of uniform applications of fertiliser
R. HORRELL1, A.K. METHERELL2, S. FORD3 and C. DOSCHER4
Proceedings of the New Zealand Grassland Association 61: 215–220 (1999)
Abstract


Over two million tonnes of fertiliser are applied to New Zealand pastures and crops annually and there is an increasing desire by farmers to ensure that the best possible economic return is gained from this investment. Spreading distribution measurements undertaken by Lincoln Ventures Ltd (LVL) have identified large variations in the evenness of fertiliser application by spreading machines which could lead to a failure to achieve optimum potential in some crop yields and to significant associated economic losses.
To quantify these losses, a study was undertaken to calculate the effect of uneven fertiliser application on crop yield. From LVL’s spreader database, spread patterns from many machines were categorised by spread pattern type and by coefficient of variation (CV). These patterns were then used to calculate yield losses when they were combined with the response data from five representative cropping and pastoral situations. Nitrogen fertiliser on ryegrass seed crops shows significant production losses at a spread pattern CV between 30% and 40%. For P and S on pasture, the cumulative effect of uneven spreading accrues, until there is significant economic loss occurring by year 3 for both the Waikato dairy and Southland sheep and beef systems at CV values between 30% and 40%. For nitrogen on pasture, significant loss in a dairy system occurs at a CV of approximately 40% whereas for a sheep and beef system it is at a CV of 50%, where the financial return from nitrogen application has been calculated at the average gross revenue of the farming system.
The conclusion of this study is that the current Spreadmark standards are a satisfactory basis for defining the evenness requirements of fertiliser applications in most circumstances. On the basis of Spreadmark testing to date, more than 50% of the national commercial spreading fleet fails to meet the standard for nitrogenous fertilisers and 40% fails to meet the standard for phosphatic fertilisers.
This paper has info on spread patterns and economics (paper attached)
Precision farming: adopt or perish?
I. YULE
Institute of Technology and Engineering, Massey University, Palmerston North
Proceedings of the New Zealand Grassland Association 61: 209–214 (1999) 209
Abstract
Precision farming has captured the imagination of many in terms of what it can offer. It is based on simple ideas that appear to make perfect sense. Firstly: feed a crop only to its potential in that particular location. Secondly: spray and treat only those areas that require treatment for control of disease and weed problems. This technique offers improved profits through increased yield as well as potential savings in input costs. There are however additional costs that must be met. These include a global positioning system (GPS), additional controllers and monitoring devices on machinery, data storage devices on vehicles and additional software to manage and analyse the data produced. Much of the work completed around the world has been directed towards combinable crops, there are however increasing numbers of yield mapping systems being developed for other machines such as forage harvesters, grape harvesters and root harvesters. Indeed higher value crops would appear to offer greater potential for increased profit. This paper examines the technology adoption process and discusses some of the issues likely to affect adoption of precision farming here in New Zealand.
Control systems are now being used on a number of farm implements. One of the most advanced areas is in fertiliser application. These systems are designed to assist the operator in accurate spreading. For example, spinning disc speed is monitored and should it go out of range, the driver will receive a warning. A higher level of control can be achieved when used in conjunction with the tractor’s radar speed sensor. If the tractor’s speed increases or decreases then the feed gates from the hopper will adjust automatically to give the correct fertiliser rate. It is the next logical step to use the same method to adjust the spread rate on the move. A fertiliser application plan is formulated according to a number of criteria. The equipment is used in conjunction with a DGPS receiver and when in a given position it recognises what application rate should be applied. The gates are adjusted through linear actuators, these move the feed gates to a position which has been calibrated to achieve the desired spread rate. Calibration is extremely important and must be completed for each product used over a range of spreading rates, this is termed “multi-point” calibration.
Achieving accurate discharge rates and spread pattern is vitally important, the next element is to make sure that the machine is in the correct position. A guidance system based on a Trimble Ag132 DGPS receiver was trialed on pasture by the author and found to be extremely beneficial in terms of getting the driver to drive at the correct spacing. A number of experiments were conducted to ascertain the level of accuracy of student drivers. Using guesswork, the spreader was within 1 m of the correct position only 27% of the time and for 40% of the time, had an error level greater than 2 m. A 16% overapplication of fertiliser occurred for two main reasons; not matching swath width and not keeping swaths parallel. Using a DGPS guidance system improved performance markedly to a point where 96% of all positions measured were within 1m and 61% of recorded positions were within 0.5 m of their required position.
Economic performance
Embarking on precision farming has significant costs and the expectation should be that these will be returned through improved economic performance brought about by increased yields and improved utilisation of fertiliser and sprays. Sensitivity analysis for most crops reveal that increasing yield should still be a higher priority than savings in fertiliser alone. Blackmore (1994) reported savings in fertiliser cost of 17–22%. This would correspond to the level of saving required to break even for a 200 ha arable property investing in precision 213 farming technology. However, increasing yield at the same input cost has a far greater financial benefit.
This technology is much less expensive in 1999 than previously and we can calculate the costs on the basis of the following estimates.
Yield meter on header NZ$10,000
DGPS receiver NZ$8,000
Control system for fertiliser spreader NZ$5,000
Annual fees for correction signal NZ$3,600 *
Annual cost of software upgrades and maintenance NZ$1,000
*Provision of UHF differential signal through Satlink, Christchurch.
Using a simple calculation, the average cost per annum can be estimated. Assuming an 8-year write-off and an interest rate of 10%, the average annual operating cost for the extra equipment would be $5,169 without
the correction signal fee. The annual fee for the correction signal is a major additional cost which would bring the annual operating cost up to $8,769. Some service companies realise this is too expensive and are
trying to offer the service for around $1,000. It is also possible to pay for only the months that you use the
service, i.e., pay $1,800 for 6 months. Earl et al. (1996) calculated the economic benefit of precision farming to be £33.68/ha (NZ$100) based on the series of assumptions stated in Table 4. Their UK scenario suggested an equipment cost of £9,480 (NZ$28,440), the net benefit calculated over 250 ha was £4,372 (NZ$12,817), or £17.09/ha (NZ$51.27). Although reductions in cereal price have taken place, there would still be a net benefit of £11.09/ha (NZ$33.27) for wheat at £80/t (NZ$240). If similar results could be achieved with higher value crops, then clearly there are tremendous potential financial benefits to be gained from using this technology.
Table 4: Assumptions made by Earl et al. (1996) on pricing of
commodities and capital items for cost benefit analysis.

Prices
Wheat £100/t
Nitrogen £0.35/kg
Subsoiling Nix 1995) £50/ha
DGPS License fee £390/year
Capital Costs
Software £1,260
Combine kit £6,220
Fertiliser kit £2,000
Total £9,480

Other products such as vehicle guidance systems for fertiliser and spray applications can dramatically improve the accuracy of applying products. Farmers should get away from the idea that our present level of performance in applying fertilisers and sprays to crops is acceptable, it is not and should be improved regardless of whether precision or conventional farming methods are practised. Yule & Crooks (1996) estimated a financial loss due to inaccurate spreading on a UK arable rotation of two wheat crops, barley and oilseed rape. Where the spreader had a coefficient of variation in spread pattern of 15% the cost was £4.00/ha (NZ$12.00), where the coefficient of variation increased to 25% the cost was £10.00/ha (NZ$30.00). These values for spreader performance were well within the range found on UK farms.
Conclusion
Adopting these new techniques is not a take it or leave it situation. Parts of the package can be used. Indeed the first step in the process of achieving greater precision in our existing operations may be the most beneficial step to take. We should not be fooled into thinking that precision farming is the “holy grail”, indeed it is only part of a much wider technical revolution in farming. We must become “a smart industry” if we are to take our farming systems to the next level. We should not delude ourselves into believing that the present situation is good enough. It costs the same to drive a tractor up and down a paddock spreading fertiliser or spraying chemicals accurately as it does inaccurately, so why is our performance so poor? We are not utilising our present generation of farm machinery to its potential; clearly, before we adopt these new technologies we need to change attitudes as well as upgrading technical skills. Education and training are essential to make sure we improve upon the current situation. Because product quality will become as important as quantity in determining financial success, much better control of our farming system is essential, especially in relation to the growing of a new generation of crops such as pharmaceuticals, nutraceuticals and genetically modified crops. Better control will also need to be demonstrated to satisfy an increasingly aware and weary consumer. This is especially the case in many of New Zealand’s main export markets. Supermarkets are responding by requiring a much greater level of product information on the food they are retailing. Once some these basic problems have been tackled, then we should design our own adoption timetable for precision farming. The technology is ready but as producers, are we ready to adopt it?
Application of the nutrient budgeting model OVERSEERTM to assess
management options and Regional Council consent requirements on a Hawke’s Bay dairy farm
S.F. LEDGARD1, G.A. EDGECOMBE2 and A.H.C. ROBERTS1
1AgResearch Ruakura Research Centre, Private Bag 3123, Hamilton
2Hawke’s Bay Dairies Ltd., RD9 Matapiro Road, Hastings
Proceedings of the New Zealand Grassland Association 61: 227–231 (1999) 227
This paper presents information on the effects of different farm management practices at Hawke’s Bay Dairies Ltd. on N flows, as estimated using OVERSEER. Outputs from the model relative to measured N flows in farmlet studies at the Dairying Research Corporation (DRC) Number 2 Dairy are also presented.


Geospatial Information & Agriculture 2001 Conference
Precision Management of Fertiliser Application to Pasture
Allan G Gillingham
Table 1: Comparative economic returns from uniform and differential fertiliser application to contrasting hill farm types (modified from Gillingham et al. 1999).
Hill farm type
Uniform fertiliser
Differential fertiliser
% Difference
Net Margin ($/ha)
Net Margin ($/ha)
Moist-Low fertility
161
173
7.5
Moist-Mod fertility
228
250
9.6
Summer dry- Low P+N
185
266
43.0
Summer dry-High P
246
8.1
Figure 1: Differential pasture growth zones A, B and C in Paddock 43 Massey University No 1 Dairy; June 2000, and associated responses to N fertiliser in each zone (from Gillingham and Betteridge, 2001
How can my position on the paddock help my future direction?
Chris Rizos
School of Geomatic Engineering
The University of New South Wales
Sydney NSW 2052
Tel: 02-93854205, Fax: 02-93137493
Email: c.rizos@unsw.edu.au
Abstract
GPS is the positioning technology of choice for a wide range of land-based applications. Since the mid-1990s GPS products have been on offer for the 'agricultural market'. GPS on its own does not appear to contribute much to improving agricultural productivity. Hence 'precision agriculture' has generally referred to the integration of GPS within a total system that, for example, uses spatial information on soil quality to deliver variable quantities of fertiliser. Hence, the GPS technology is just one element of a total vehicle-borne system, and may not even be the most expensive or problematic component. If crop yields do indeed improve through the application of such a system, then one would expect the GPS technology to be wholeheartedly embraced. Trends in the GPS receiver technology necessary for positioning at the few metre accuracy level will be reviewed. However, GPS-guided agricultural vehicles place similar demands on precise positioning (centimetre to decimetre level accuracy) technology that mining, excavation and industrial vehicles do. Hence, precise GPS positioning developments in areas such as field robotics are expected to deliver improved performance for agricultural vehicles as well.
extract
(3) Farm machinery guidance/control is an additional desirable application. GPS guidance will aid the farmer to plow, seed, apply fertiliser/pesticide, water, and finally harvest fields in an efficient manner. That is, ensuring that such row operations do not 'miss' parts of the field, or preventing an overlap of such operations. In such cases decimetre level accuracy is needed. However, sub-decimetre accuracy would be required if vehicle guidance (and ultimately control) must ensure true 'parallel tracking' across the field, so that the machinery tyres always travel down the same 'ruts'. This is the most challenging of the GPS applications in 'precision agriculture'.
It can be seen that the GPS accuracy requirements for 'precision agriculture' fall neatly into two broad groups: few metre to dekametre accuracy for mapping and VRT, and cm-dm accuracy for machinery guidance/control. The former can be satisfied using SPP or DGPS pseudo-range-based techniques, while the latter requires carrier phase-based techniques.
To conclude, whilst the maximisation of yield has been a significant motivation for the environmental factors and traceability issues that will be the drivers in the future. It is anticipated, however, that this will be supplemented by the requirements for bio-fuels and the resulting pressure on the land to provide for food, feed, fibre and fuel. This is becoming a strategic issue but unfortunately one not yet felt by the currently struggling agricultural industry. (Richard John Godwin, PRECISION AGRICULTURE TOOLS FOR
SUSTAINABLE SOIL AND LAND MANAGEMENT, 2006)
Comparison of fertilizer strategies for reducing nitrate leaching from grazed grassland, with particular reference to the contribution from urine patches
S. P. CUTTLE a1c1, R. V. SCURLOCK a1 and B. M. S. DAVIES a1
a1 Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK
Abstract

The effectiveness of alternative fertilizer strategies to control nitrate leaching was investigated in a field experiment at IGER, Aberystwyth using simulated pastures to represent swards grazed by dairy cattle between May and October 1997, following an initial silage cut. Cut-plots with and without applications of artificial urine were used to represent the separate components of grazed pastures managed with the following nitrogen (N) fertilizer strategies: standard (fertilizer applied uniformly to all areas of the sward at a total rate of 180 kg N/ha between May and October), tactical (fertilizer rates adjusted to match the average soil mineral-N content of the pasture to that of ungrazed reference plots receiving the standard rate) and patch-avoidance (fertilizer applied at the standard rate but withheld from areas that had received urine). Calculated stocking rates derived from herbage yields indicated that 12% of the pasture would have been affected by urine up to the end of ‘grazing’ in October. The presence of urine patches increased the nitrate-N content of the 0–90 cm soil profile in October from 61 kg N/ha for ungrazed pasture to 104 kg/ha for ‘grazed’ pasture receiving the standard fertilizer rate. Although the patch-avoidance strategy was more effective than the tactical in reducing the accumulation of nitrate in soil under urine patches, they were both of limited effectiveness in reducing the content over the pasture as a whole. Profile contents in October for the simulated pastures managed with the tactical and patch-avoidance strategies were equivalent to 99 and 97 kg nitrate-N/ha, respectively. The tactical strategy achieved a 26% saving in overall fertilizer use. Under the conditions of the experiment this did not significantly reduce herbage yields. The patch-avoidance strategy reduced fertilizer use by only 3%.