The impact and benefits of variable rate seeding

That is a key conclusion of a study of the Vytautas Magnus University in Lithuania. The main objective of the study ‘Variable Rate Seeding in Precision Agriculture: Recent Advances and Future Perspectives’ (2022) was to analyse variable rate seeding (VRS) methods and critically evaluate their suitability and effectiveness for the challenges under field conditions.

The researchers analysed and evaluated 92 variable rate seeding methodologies, their impact and economic benefits depending on the main parameters of the soil and environment.

They point out that a site-specific sowing method – with a variable sowing rate for each field area – allows the optimisation of crop density to obtain the best agronomic and economic results. Various proximal and remote sensor systems, contact and contactless equipment, mapping and VRS modelling technologies are currently used to determine soil and crop variability.

The researchers highlight numerous practical examples that demonstrate the effect of variable rate seeding. According to a study of German researchers, it is effective to apply VRS when the apparent electrical conductivity changes in the field on average every 25 metre and for NPK (nitrogen phosphorus potassium), when the pH changes on average every 50 metre.

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The payback of variable rate seeding

Variability in apparent electrical conductivity, organic matter and terrain leads to variability in plant density. The researchers emphasise it is therefore useful to also apply a variable rate of nitrogen. They say that the payback of variable rate seeding is such that if a farmers earns an average of 100 euro (US $109) per ha, then working on 400 ha will pay it off in 1 year.

The researchers conclude that it is most efficient and most profitable to apply VRS when the farm size is larger than an average of 150 ha. However, this also depends on the crops grown (possibly smaller) as well as the satellite maps used.

Due to meteorological conditions, if satellite maps are used, clouds can cause problems. Therefore, it can be better to apply remote and proximal sensors close to the ground, which are effective in all meteorological conditions, according to the study.

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VRS efficiency

The key conclusion is that the higher the field variability (altitude, terrain, sand, etc.), the higher the VRS efficiency and payback. As variable rate seeding has been shown to be profitable for fields with very diverse soil productivity, quantitative assessments of field variability should be taken into account when deciding whether to use VRS.

In a study in southern Brazil, researchers evaluated VRS by creating zones based on data from the producer on (corn) field productivity levels, as well as eight-year of yield data. The seeding rate of low-yield potential areas decreased and productivity increased in the areas by 1197 to 1900 kg per ha. The population level of potential soil management zones (MZs) with high soil fertility increased and productivity there increased by 888 to 942 kg per ha.

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The effect of different seed quantities

Economic return is of course also a key issue for farmers interested in VRS. Lowenberg-DeBoer looked at VRS economic return, using zones of yield potential. Potential VRS savings could be around USD 6.25 per ha in the fields of various seeding populations. These savings from VRS can be effective in the face of rising seed prices.

With digital tools and field-based data collection, VRS can enable farmers to explore and fully implement VRS and reap the economic benefits of doing so. Data from an economic analysis of wheat show the effect of different seed quantities and different N levels.

It is clear from the data that seeding 120 kg per ha yields the highest net income while 60 kg per ha yields the lowest net income. The highest net profit was observed by combining the 120 kg per ha seeding rate and 120 kg N per ha quantity of fertilizer, while the minimum profit was obtained when the seeding rate of 120 kg per ha was applied and nitrogen fertilizer was not used.

The highest marginal rate of return was observed by combining 120 kg N per ha and 120 kg per ha seeding rate and the lowest marginal rate of return was found in control plots seeded at 60 kg ha.

Several researchers have analysed the economics of site-specific seeding (SSS) in terms of economic plant population, degree of field variability, cost-effectiveness of VRS technologies, seed consumption and yield.

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Reducing losses due to excess nutrients

Bullock and others found that the optimal density of specific site seeding corn seeds ranged from 44,000 to 104,000 seeds per ha, and the yields ranged from 5.1 to 18.3 Megagram per ha. Modelling showed that by practicing VRS, farmers could increase their income up to USD 12 per ha, compared to a uniform seeding rate.

Taylor and others assessed the potential of specific site seeding in eastern Kansas, USA for three years and found that specific site seeding was not profitable under the cultivation conditions studied. They suggested looking for a cheaper method to make SSS economically feasible.

It is generally accepted that a too high or too low seeding rate is sub-optimal, so there must be some economically justified optimal seeding rate value or range of values. An economic analysis by Holmes revealed that VRS is a valuable tool for reducing losses due to excess nutrients in poor quality crops. Seeding at a variable rate ensures optimal use of other agricultural raw materials, such as fertilizers.

VRS eliminates double sowing in headlands and point rows and redistributes the optimal number of seeds in very heterogeneous fields. In very uniform fields, the return on investment of VRS will be low, while in heterogeneous fields with differentiated soil productivity zones, the return on investment will be much higher.

Automatic section control

Automatic technology for the control of seeding rows (sections) enables automatic control of the seeding sections using the seeding map to reduce the field areas that can be seeded twice due to overlap, another study points out. Automatic section control can on average save 4.3% of seeds, as well as reduce corn yield losses by 17% compared to seeding methods that inevitably cause double-sown areas.

With VRS, the total number of seeds used in the field can be lower, leading to lower greenhouse gas (GHG) emissions from seed production. The positive impact of VRS on GHG emissions may also be due to higher yields. Another GHG reduction measure is related to the lower amount of fuel required to produce the same yield.

Summarising the literature analysis, personal experience and unpublished assessments, the researchers conclude that the application of VRS pays off when the field variability is more than 10%.

Ensure precision production

Advances in seeding technology for the implementation of VRS make it possible to make better use of soil variability, the researchers conclude. VRS allows the population to be adapted to the variability of the field and helps to ensure precision production in the field in order to reduce errors in the seeding process.

Another important aspect is that interest in VRS around the world is growing due to the interaction of these technologies with current seed prices. An optimal plant population can improve crop yields while maximising farm profits.

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Depth of insertion during seeding.

A site-specific seeding method, where variable seeding rate is applied to each field area separately, makes it possible to optimise crop density in anticipation of the best agronomic and economic effect.

Various proximal and remote sensor systems, contact and contactless equipment, and mapping and remote and proximal sensors, mounted on tractors or off-road vehicles, help to create field maps of variable properties. The accuracy of these maps and the good assignment of field soil management zones are currently the successful outcomes of VRS.

New research methodology

The researchers emphasise that new research methodology should be developed while considering soil heterogeneity, using telemetry systems and multifunctional ultraviolet (UV), optical (VIS) and near-infrared (NIR) spectroscopy methods to optimise the number of seeds per unit area and depth of insertion during seeding.

The multifunctional model for sustainable precision seed technology control based on UV–VIS–NIR spectrometry will allow farmers to save seed, to make better use of soil, to increase plant productivity, to protect the environment and to reduce energy consumption and economic costs.

“In all future studies, it is especially important to test and evaluate the latest methodologies in practice on farms and then to make complex assessments of the soil, plant and environmental parameters, and changes in the proposed methods in order to find the best solution and the most optimal methods for farmers”, the researchers say.