تجزیه و تحلیل اقتصادی بالقوه برای کشاورزی دقیق در تولید غلات انگلیس

The results from alternative spatial nitrogen application studies are analysed in economic terms and compared to the costs of precision farming hardware, software and other services for cereal crops in the UK. At current prices, the benefits of variable rate application of nitrogen exceed the returns from a uniform application by an average of £22 ha−1 The cost of the precision farming systems range from £5 to £18 ha−1 depending upon the system chosen for an area of 250 ha. The benefits outweigh the associated costs for cereal farms in excess of 80 ha for the lowest price system to 200–300 ha for the more sophisticated systems. The scale of benefits obtained depends upon the magnitude of the response to the treatment and the proportion of the field that will respond. To be cost effective, a farmed area of 250 ha of cereals, where 30% of the area will respond to variable treatment, requires an increase in crop yield in the responsive areas of between 0·25 and 1.00 t ha−1 (at £65 t−1) for the basic and most expensive precision farming systems, respectively.

The potential benefits of managing crops using precision farming techniques include: (1) the economic benefit of an increase in crop yield, and/or a reduction in inputs, i.e. seed, fertiliser and agrochemicals, and (2) the environmental benefit from a more precise targeting of agricultural chemicals. Over the past decade, the technology has become commercially available to enable the farmer to both spatially record the yield from a field (Murphy et al., 1995; Birrell et al., 1996; Stafford et al., 1996) and vary both seed and fertiliser rates on a site-specific basis. Significant advances have also been made (Miller & Paice, 1998) to permit the spatial control of weeds on a site-specific basis by varying the dose rate of herbicides depending upon the weed density. However, the benefits of either an increase in yield and/or a reduction in fertilisers and agrochemicals have to be offset against the costs of investing in specialist equipment to enable yield maps to be produced and variable applications to be implemented. The aim of this paper is to address these issues. A range of potential benefits have been reported, from various combinations of different variable application rate practices. Earl et al. (1996) postulated a potential benefit of £33·68 ha−1 could be possible combining variable nitrogen application and targeting subsoiling to headlands for a crop of wheat in the UK, when wheat prices were £125 t−1. Increases in returns exceeding £57 ha−1, when maize seed rates were varied according to soil depth, were reported by Barnhisel et al. (1996). Measured returns in the range of −£11·14 to £74·09 ha−1 were reported by Snyder et al. (1998) on irrigated maize in the USA. Schmerler and Basten (1999) measured an average benefit of £38·60 ha−1 when growing wheat on a farm scale trial where both seed and agrochemical rates were varied. Studies conducted by James (2000) investigated the benefits of using historic yield data as a guide to varying nitrogen application, for winter barley on a field with both clay loam and sandy loam soil types. Data from the first years results, i.e. 1997 harvest reported by Godwin et al. (1999), indicated that an economic benefit of £27·60 ha−1 could be possible. This analysis was based upon spot measurements of the yield rather than those for the complete zone in either soil type, however, it is generally indicative of the potential benefits. A further part of the experiment applied nitrogen based upon the calculated value of the most economic rate of nitrogen (MERN) and nitrogen rate for maximum yield (NMAX) in the previous year, after the principles developed by Kachanoski et al. (1996). The main conclusions of this research were that: (1) the maximum yield of the response curve for each soil type (NMAX) occurred at the same application rate in each growing season, (2) the MERN for each soil type were not significantly different, and (3) based on yield information from previous yield maps, there was no simple variable rate application strategy that provided a yield or economic benefit compared to a uniform application of nitrogen fertiliser. The work reported in Godwin et al. (1999) also demonstrated the effect of the nitrogen/grain price ratio on the economic return to variable application of nitrogen and that at 1999 prices of £80 t−1 for grain and £0·30 kg−1 for nitrogen the MERN rates were 15 to 30 kg ha−1 lower than NMAX. The costs of implementing precision farming practices have been reported by a number of researchers. Earl et al. (1996) estimated the costs of yield map production and the ability to apply fertiliser on a site-specific basis to be £10·46 ha−1 for an arable area of 250 ha, at 7% interest rate amortised over a 5-yr period in the UK. A later estimate of £7·81 ha−1 was made by James (1998), for a similar system, the difference in cost being the reduction in hardware and software cost over the 2-yr period and the removal of the differential global positioning system (DGPS) costs. In the same year studies, in the USA, Snyder et al. (1999) estimated the cost of yield mapping and variable rate equipment, for nitrogen application for two fields of 49 and 64 ha as £8·50 ha−1. Studies by Schmerler and Basten (1999) reported costs of £15·46 ha−1 (49DM ha−1) for a 7100 ha German farm, of which 3900 ha was suitable for site-specific management. The major reason for the higher figures reported by Schmerler and Basten (1999) was the cost of the equipment variably applying herbicides in addition to variably applying seed rate and fertiliser.

These conclusions are based upon nitrogen and cereal prices at £300 t−1 and £65 t−1 respectively, and for equipment prices in the UK in January 2001. (1) At the above prices the benefits of the variable rate application of nitrogen, based upon crop canopy management using aerial digital photography compared to a standard uniform rate provided an average improvement of £22 ha−1. This was based upon the results of eight experimental strips in two fields of wheat, with a range of seed rates. The fields were located in Southern and South Eastern England and represented soils similar to 30% of the arable growing area of England and Wales. (2) Applying nitrogen fertiliser based upon the variations in historic yield is not economically justified. (3) The capital cost of yield mapping and variable application equipment varies from (a) basic precision farming system (£4500) which uses a non-differential global positioning system with the yield monitor to produce a yield map and a forward speed indicator to advise the operator of the target speed needed to achieve the required application rate, to (b) differential global positioning system equipped unit with greater spatial accuracy and automatically controlled variable application systems ranging in cost from £11500 to £16000, depending upon the level of integration and compatibility with existing farm machinery, the most expensive system permitting both yield mapping and spatially variable application to be undertaken concurrently. (4) The annual cost per hectare of the above equipment over a 5 yr depreciation period, at an interest rate of 8.5% together with maintenance and training vary between £4.67 and £18.46 ha−1 for the basic and most expensive system, respectively, for an area managed by the precision farming system of 250 ha. These costs will change in inversely with area managed per unit. (5) The benefits outweigh the additional costs of the investment in precision farming systems and services for cereal farms greater than 80 ha for basic low-cost systems and 200–300 ha for the range of the more sophisticated systems. These figures also assume a £7 ha−1 charge for crop canopy images either from aerial or ground-based systems. (6) The costs of detailed soil analysis prohibit collection from a dense grid of data points and targeted sampling based upon significant variations in yield or soil type is recommended. (7) Common problems, such as water logging and fertiliser application errors, can result in significant crop yield penalties. Precision Farming can enable these problems to be identified, the lost revenue to be calculated and the resultant impact on the cost/benefit to be determined. This provides a basis from which informed management decisions can be taken. (8) Work carried out by other researchers indicates that savings in herbicide use of the order of £0·50 to £20·70 ha−1 can be made. (9) Currently aerial digital photography appears to be less expensive than tractor mounted radiometers (TMR)for collecting normalised difference vegetation index data; however, ‘real time control’ of nitrogen based on a TMR system offers the least cost option. (10) The scale of the benefits obtained from precision farming practices depends upon the magnitude of the response to the corrective/variable treatments and the proportion of the field which will respond. Typically a farmed area of 250 ha of cereals, where 30% of the area will respond to corrective/variable treatment requires an increase in yield on the responsive areas between 0·25 and 1·0 t ha−1 for the basic and the most expensive system, respectively. These figures will change in inverse proportion to (i) the size of the area managed with each precision farming system and (ii) the percentage of the field that will respond to treatment.