Just like humans, for healthy and proper growth plants need one thing above all: a balanced diet. Not too much, not too little, and crucially in the right combination. Plants take their “meals” in the form of minerals from the soil; these are taken up via the roots and stored and processed in shoots and leaves. Wild plants get their nutrition from mainly undisturbed soil, where they live together with other plants. Replenishment from dead material and its transformation by micro-organisms in the soil takes place in a well-established rhythm.
Our crop plants, however, are “high-performance athletes”, which grow in a cleared field and subsequently are mostly removed from there before the next crop rotation element is planted. Responsibility for the nutrition of these athletes lies with the farmer. On one hand, by taking care of his soil fauna, which he supplies with basic dressing and with intermediate crops and crop residues. And on the other, by fertilizing the crops, because without a balanced cocktail of essential and micro-nutrients, which is composed differently for each type of plant, our plant athletes cannot perform.
Luckily we have a very good knowledge of their needs and the development stages at which these needs arise. The crops’ hunger for certain plant nutrients can be satisfied by means of agricultural fertilizers such as slurry or manure or by mineral fertilizers. The latter are either produced from natural resources such as potassium salts, phosphates or lime, or manufactured industrially, as single-nutrient or complex fertilizers optimally tuned to the needs of plants.
However, the question now arises as to how the food gets to the root – in the right quantity, at the right time and in precisely the right place. This precise supply of nutrition, with which the production potential of the plant is used efficiently, is of course balanced by economic considerations. Because efficiency – derived from the Latin word efficientia (effectiveness) – is measured primarily by whether things are done correctly from the economical point of view – in order to achieve the best possible result. In the last decades, agricultural technology has produced and continually developed many designs of machines to provide crops precisely and efficiently with nutrients. Now, since the circumstances of production – farm size, local conditions, crops grown, regional characteristics – are as variable as the weather in April, these requirements cannot be met with just one technology.
“Dietary guidelines” from the legislator
And then there is another factor influencing methods of fertilization: the legislator. European and national legislative packages insist more and more on conserving operating resources, and the same is true for fertilization. Ultimately this all has to do with efficiency, it’s all about getting the remaining amounts into the plants as precisely and with as little loss as possible.
A great deal of development work has been done here in past years. The familiar systems have been refined by the manufacturers: In particular the opportunities for data capture and on-time assessment help to make application more precise, help implement the guidelines of the Fertiliser Ordinance, and not least, help reduce the burden on drivers.
Technologies for mineral fertilization
For decades, mineral fertilizers were spread on fields by hand, later with box spreaders – drawn by horses and with an operating width of 2.5 m. Our modern centrifugal spreaders with operating widths of up to 50 m and outputs of up to 20 ha/h are in a totally different league – and they need to be, after all, they’re feeding high-performance athletes.
Centrifugal spreaders: Meals on wheels
Centrifugal fertilizer spreaders are the most widely used systems: Fertilizer granules run out of the hopper onto two rotating spreader discs, which use throwing vanes to accelerate them and throw them out and away from the spreader. These exist as mounted and towed variants, with hopper sizes up to 4,000 l (mounted) of 22,000 l (towed, two axles) and with operating widths of 24 to 36 m, and some even up to the 50 m mentioned above.
The spreaders are currently mechanically or hydraulically driven; in the future, more and more manufacturers are opting for electric drives. The material properties of the fertilizer affect the spread width as well as the spread pattern. For this reason, it is extremely important to set the spreader precisely in order to avoid spreading errors. Details about this are available not only from agricultural equipment providers, but also from fertilizer manufacturers and the official consultants.
Pros and cons: Centrifugal fertilizer spreaders are widespread, practical, powerful and comparatively cheap. The short set-up times area also a plus in labour-intensive phases. Numerous innovations to improve the spreading quality allow overlapping and spreading errors to be minimized and legal requirements to be complied with. These innovations include boundary spreading devices, sensors to regulate the accuracy of distribution, GPS or electric, finely adjustable drives.
The technology also has a whole range of minus points, among others limitations on the hopper size and the associated axle loads. Also vulnerability to wind and the reliance on size and composition of the fertilizer granules, which require constant checks and readjustments in order to guarantee the accuracy of distribution.
The surface application of mineral nitrogen fertilizers can result in natural losses in the air or due to leaching into the soil. These can be limited by applying urease and nitrification inhibitors and by subsequent working-in. However, if lack of precipitation allows an application of nitrogen to become effective too late or not at all, this is difficult to influence.
Pneumatic spreaders: Direct to the plants
With distribution by pneumatic spreaders, the fertilizer is fed from the hopper to the metering unit and from there is delivered to the distribution nozzles by the air stream via pipelines. Metering is done by cam wheels which are driven by hydraulic motors and can be continuously adjusted.
Pros and cons: The pneumatic spreader proves its strengths especially in windy regions. The accuracy of distribution is considerably better when finely granulated fertilizers such as urea or mixtures with a wide range of granule sizes are to be applied. The continuous adjustment and part-width control allow precise application. A disadvantage is that, as with the centrifugal spreader, fertilizers are applied above ground, from where they must first reach the root without loss.
Placed exactly rather than widely distributed
Fertilizer placement, i.e. the placement of fertilizer underground close to the root, follows a completely different philosophy. There are many procedures, depending on the fertilizer used and the crop. This technology is most suitable for the application of nitrogen and phosphorus. Common to all these procedures is the attempt to bring the nutrients to and into the plants better, to thus increase the nutrient efficiency, and to fulfil the pressure of legal requirements. However, many of the procedures are not yet fully developed.
It is a great advantage that using this technology, sowing and fertilization can be combined and thus – in addition to the precise, weather-independent placement of fertilizer close to the root – several work steps can be combined.
Particularly for maize and increasingly also for potatoes, there is the now established procedure of side-dressing. Here, in order to avoid salt damage to seedlings, the fertilizer band is laid about 5 cm below the seed and about 5 cm to the side of the seed row.
Also for sowing maize, but also for rape and cereals, sowing technology manufacturers offer the procedure of under root fertilization, in which the fertilizer band is not laid at seed level, as with side dressing, but much deeper, at the processing level of the coulter. This procedure is intended to encourage the roots to grow deep.
Seed row placement with microgranulate is another modern form of fertilizer placement. Here, during sowing, fertilizer is also laid in the seed row directly on the seed grain, using a microgranulate metering feeder. Thanks to the specially configured granulate, the close proximity to the seedling does not lead to salt damage. The nutrients can thus be tapped quickly and in early stages of plant development.
Pros and cons: An unbeatable advantage of this procedure is of course the timely and demand-based availability of nutrients according to the requirements of the young plant. This even works with inadequate water provision, unfavourable pH values, unfavourable soil structures or cold and wet weather. Thanks to the stabilized fertilizer, the total mineral nitrogen fertilization can be combined in one application, without the fear of nitrous oxide emissions or nitrate leaching into groundwater. The supply of plants with “fertilizer deposits” from which the necessary nutrients are released over a long period has clear advantages for plants, the environment and the farmer.
Disadvantages are the higher investment costs of the systems.
Nutrition in liquid form
Mineral fertilizers can of course now be applied to plants in liquid form as well as in solid form. Their application is possible in various ways: Firstly with the field sprayers usual in crop protection, or with special spreaders which work them into the soil punctually. If field sprayers are used, it must be borne in mind that such liquid fertilizers can be caustic and corrosive. Therefore components that come into contact with them must be made from corrosion-resistant materials, such as stainless steel, plastic or ceramic. Of course, such aggressive liquids can also cause damage to crops. To avoid burns, they can also be applied directly to the soil using drag hoses.
Food on a leaf
A special form of liquid fertilization is foliar fertilization. It can be used in particular for nitrogen, magnesium and sulphur. For phosphorus, potassium and calcium it is less suitable due to the higher quantities required. The foliar application of trace nutrients is widespread; however this can equally well take place prophylactically in the event of visible signs of deficiency, i.e. with acute deficiency. A cocktail of different trace nutrients can easily be administered in combination with a plant protection measure.
Pros and cons: The combination with plant protection measures saves on machine usage. At the same time, an application of essential or trace nutrients can balance an acute deficit. It is extremely effective, because the degree of efficiency of the nutrient supplied to the plant via the leaf is up to five times higher than for nutrients applied via the soil. However, it cannot replace soil fertilization, particularly for essential nutrients, but can only supplement it, as the quantity required cannot be covered by the limited absorption capacity via the leaf.
Cultan: Food from wheels
The second form of liquid fertilization with special spreaders, already mentioned above, is a variant of nitrogen depot fertilization which has been tested over many years in the prairies of North America due to the environmental conditions there: the liquid injection of highly concentrated nutrients into the soil. Furthermore, Cultan fertilization is also possible with solid fertilizers. “Cultan fertilization”, developed here in Germany by Prof. Sommer since the 1970s – Cultan stands for Controlled Uptake Long Term Ammonium Nutrition – can ensure the supply of ammonium-nitrogen and phosphate especially in cereals, maize, rape, potatoes, on grassland and in vegetable cultivation. With this procedure, fertilizer is placed 7 to 20 cm deep and slightly to the side of the seed rows. The deposits are not washed out or transformed by microbes. The plant roots grow around them and take up the nutrients until it is used up at the end of vegetation. The procedure is winning over more and more support as it is used, the areas treated in this way are growing constantly. Environmental associations also find this strategy very good, due to the reducible quantities of fertilizer and the low environmental impact. Several generations of machinery exist, the latest innovation is high pressure injection, where the fertilizer solution is “shot” into the soil under high pressure.
Pros and cons: Injection allows the fertilizer to be worked in without loss. The degree of efficiency for nitrogen can thus reach 100%, and GPS support enables very precise working. Wash-out is avoided, the Nmin values after harvesting are low. For the crops, improved nutrient efficiency, demand-based supply and lower susceptibility to stress in dry conditions are notable. Farmers are pleased with stable and sometimes higher yields and with the lower dependence on rainfall.
In addition, the technology is of course expensive and is thus only suitable for large scale operations or contractors.
In view of the number of varieties of operational structures, local conditions, crop types and their requirements, it is clear that no single technology can satisfy all requirements. However, all of them aim to deliver the right amount of nutrients at the right time without negative impact. In this respect, enormous technical advances have been made in recent years.
Scientists believe that centrifugal spreaders will continue to dominate the market in the future. However, the Fertilizer Ordinance and the removal of active substances in plant protection are accelerating the growth of fertilizer placement. Many improvements can be expected here, for example with regard to GPS controlled equipment with automated adjustment of all essential parameters. New drive systems enable more precise application, sensors assist with control and reduce the burden on drivers.