January 29, 2014
Greater Precision in Soil Understanding
A far more precise understanding of soils and their variation across every field is vital to make the most of the latest GPS-based farming technologies, believes precision agronomy specialist, John Lord.
“Modern precision technologies enable us to automatically adjust a wide range of inputs to the surprisingly wide variations in soils across our fields,” pointed out the technical manager responsible for Agrii’s innovative range of precision agronomy services. “But without accurately mapping and appreciating these variations we simply cannot tailor our inputs to make the most of them.
“We know from our long-standing SoilQuest experience that accurate soil maps produced from in-field scanning or satellite technology are far more valuable precision farming resources than those developed through either conventional whole field or grid-based soil sampling. Allied to precision sampling, they show us how the soil actually varies across the field rather than how either informed guesswork or computer predictions suggest it might.
In just the same way, our studies over the past two seasons underline the importance of moving beyond traditional manual to much more precise laser soil texture analysis. To such an extent that we’ve made laser topsoil analysis standard across our advanced precision agronomy mapping services.”
Rolling soil between the fingers to judge clay, silt and sand content – as we were all taught to do at college – is highly subjective. However precisely it’s done, one man’s silty clay loam can easily be another’s clay loam and a third person’s sandy silt loam.
What’s more, even the best trained hands can only accurately allocate a soil to one of eleven standard classifications. Yet within these soil types there are huge variations in actual particle size distribution. A clay loam, for instance, can be anything from 30% to 50% clay, 50% to 75% silt and 30% to 60% sand.
This wouldn’t matter but for the fact that such differences in content can have a major impact on crop establishment, nutrient behaviour, water-holding, pH correction, nutrient mineralisation, compaction risk and friability for cultivation, amongst other important crop management considerations.
“Independent laboratory laser analysis allows us to characterise soil zones within a field accurately and consistently for their actual contents of sand, silt and clay particles for the greatest agronomic precision,” explained John Lord.
“Its value is clearly illustrated in one 22 ha field we’ve mapped using both methods of soil texturing with samples taken following SoilQuest conductivity scanning. Manual texturing divides the field into two soil types – clay and clay loam. But laser analysis shows it should actually be divided into between five and nine separate zones for the best management.
“Zones within both the main soil type areas vary by a good 5% in their clay content alone. And the sand content varies by as much as 8% between zones that appear identical from manual texturing.
As well as a different approach to potash fertilisation, John Lord stresses that soils with lower clay and higher sand particle contents require a different liming strategy to those with a higher clay fraction. They are also likely to suffer compaction at a shallower depth, be more susceptible to drought at low soil moisture levels, less supportive of slugs and black-grass, and more responsive to early spring nitrogen. All of which means they could profit from different management.
“Once input plans are entered into GPS-linked variable rate sowing and application equipment it takes no more time or effort to manage five zones in a field than two,” he insisted. “So it makes sense to use the technology with as much precision as we can. Otherwise we’re really not making the most of it.
“Relatively small differences in the particle size distribution of our soils can make big differences to their properties; and, in turn, to our best strategies for liming, nutrient application and sowing, not to mention cultivation, slug and weed control.
“Knowing the precise sand, silt and clay contents of soils across our fields allows us to make the most of the precision input technologies already at our disposal. It also enables us to take the greatest advantage of new technologies for precision spraying and cultivation as they are developed.”
At the same time, John Lord stresses Agrii is using this knowledge to develop the most accurate rule sets to translate the findings of its black-grass competitiveness, soil improvement, crop nutrition and other research into the most accurate precision agronomy plans.
Add real-time information from the company’s network of weather stations, data from its automatic soil moisture probes and alerts from its increasingly sophisticated pest and disease prediction models and he sees precision farming moving up a major gear in the opportunities it offers for arable improvement. Importantly, though, he insists, it must all be built on the solid foundation of the most precise understanding of our basic resource – soil.
“To my mind, the world of soil understanding has moved on from ‘first generation’ field sampling in a simple W pattern and ‘second generation’ grid-based systems to the 3G of soil conductivity measurement,” concluded John Lord. “Laser texture analysis gives the extra precision to move us into the 4G world in which we need to be to take full advantage of modern technologies for the best-informed precision farming decision making.”