A SCANNING system which is claimed to greatly improve the accuracy of field soil testing can be used in conjunction with satellite imagery to give growers a more detailed picture of their land and pinpoint areas which are under-performing.

Precision farming expert Steve Butler, of Agrovista, outlines how it works.

The traditional ‘W’ shape used for standard soil testing supplies only limited data, because soil type can vary widely throughout a relatively small area, said Mr Butler.

It has been the standard first step towards soil nutrient analysis, but soil variation scanning could offer much greater accuracy, although he stressed that the system itself does not provide nutrient content figures.

The most commonly used soil variation scanning system is *EM, which uses equipment fixed to a sledge and pulled by quad bike, he explained. Soil variation scanning works to a depth of 0.5 metres and 1 metre and produces up to eight readings per second on a 12-metre wide basis.

“The machine uses a magnetic current in the soil to give a conductivity reading,” said Mr Butler. “It measures resistance in the soil to determine type and the data is translated into an electronic map which categorises the field into typically three to five zoned areas.

“Ideally, the non-invasive process will be carried out on stubble fields, but the machine can travel over cultivated ground or even through a crop, depending on growth stage. Nevertheless soil moisture is a significant element in the making of detailed maps and therefore the best time for the service to be carried out is either in the autumn or in the spring.”

As well as the modern EM scanning procedure, the same result can also be achieved by using the older, but equally effective, **EC scanning system. It employs a series of metal discs which are also pulled across the field surface. The technology uses an electrical pulse to measure resistance in the soil.

However, the scanner’s discs will physically penetrate the ground and therefore the timing options for conducting EC testing are more limited, he pointed out. The costs associated with the two soil variation scanning methods are the same, at approximately £12 to £15/hectare.

Soil variation scanning will typically reveal several soil differences within an average field and, more importantly, it will highlight exactly where the variation actually occurs, he added. Overlaid with other mapping information, it can give an indication of trends over a long time period and these will allow the grower to make more informed decisions.

“Some growers who have farmed land for many years may feel that they have a thorough understanding of their soils and that is largely true. However, the standard ‘W’ pattern testing can lead to inaccuracies, as there is a random element to the approach.

“In addition, growers who use the service through Agrovista are given the raw data for lifetime use, so the soil variation maps can be used for a variety of purposes at any point in the future.”

The scanning is a one-off process because soil type is a constant; it would take many decades for any significant changes to occur, he said. A thorough understanding of soil type was particularly useful when used in conjunction with nutrient testing, because this factor could affect the way that nitrogen, phosphate, potash and micro-nutrients were retained and influence fertiliser rates.

Meanwhile, data generated by soil variation scanning could be used alongside satellite biomass imagery.

“Biomass images cost about £1/hectare,” said Mr Butler. “One option for anyone starting out is to order a set of images to show establishment patterns and a second set just before harvest. The soil variation maps can be overlaid with these images and a picture will emerge, highlighting problem areas and those which are performing well. This will give the user an accurate idea about the type of soil that is producing the highest yields.

“Once this information has been obtained, the recommendation is to take a spade and dig down into highlighted areas of the field, to investigate whether there is an underlying issue. This might be water-logging, compaction, a micro-nutrient deficiency or biological issues which could be revealed through further testing. It can also be an aid for identifying which parts of the field might be taken out of production.”

These technological advancements are relatively inexpensive tools which can help farmers to better understand their soil type and maximise the efficiency of their land, said Mr Butler.

“Their greatest benefit is for farmers who routinely use precision technology. However, we also work with smaller growers to offer options which do not require investment in expensive equipment. Arable cropping presents many challenges and I feel that the use of new technologies like soil variation and biomass imagery will help farming businesses as they strive to remain competitive.”

*EM - electromagnetic

**EC - electrical conductivity