We are on the threshold of the spring campaign. It's time to feed the crops. Every year in January - even though it is forbidden - fertilisers set off into the fields. Someone here will say - but if I don't fertilise now, I won't ever get in. You will, you will. Now if you go in, you just think you're doing something ... And that's reassuring. You realise losses, you throw money to the wind - especially now with these fertiliser prices you should be more precise, you trick the plants, you disturb their dormancy, which is already fragile in the last mild winters, but you are relaxed ...

               The topic of fertilization is extensive, let's start with cereals: first, in general terms, about the timing of nitrogen fertilization - you already know, most of you practice it, the norm is good to be divided into 3 doses.

               The first dose is given before the start of vegetation, at the end of February, beginning of March, with the aim of having food readily available for the plants when they wake up and start to develop. We used to think it was better to give a large dose first. Now I think the first dose is the smaller one. I recommend 30-40% of the norm. About a month after that, or usually in early April, intense stem growth begins. Then whatever you give the plants, they take it up and absorb it. At this point almost nothing of what is thrown on the field goes to the wind. Of course there is the moisture factor. In early April, there usually is. If it doesn't have the moisture - then you just reduce the dose and you don't go into an overshoot that is doomed to fail. If conditions are good, you give 50-60% of the dose. And that leaves one 10-20% that we'll use as a corrective - either we'll save it in the drought, or if the weather is with us, we'll give it at a time for yield and quality. Now someone will say - well, there is always moisture at the first fertilization, so I will give myself the big dose then and I will not mind the drought in April. Yes, the moisture is more, but the plants are still resting, absorbing, slowly. The fertilizer either rolls off and evaporates off the top or washes off and goes down into the "sub"-soil. These are my considerations. In rapeseed the logic is similar, but there the division into 2 doses is sufficient. 40-50% before vegetation, 50-60% at stem growth. Rapeseed retains a lot of moisture and shoots up lush and thirsty before wheat.

With barley, the tactics are slightly different. It starts very intensively in early spring. First - its fertiliser rate is about 70-80% of that of wheat. And secondly, it shouldn't get nitrogen late because ... a/ multi row barley can lodge more easily and b/ brewers shouldn't build up protein. Therefore, barley can be fertilized in a 70:30 ratio, with shorter time between fertilization. Or fertilise once and then boost with foliar fertiliser and amino acids.....In any case, it is important to keep an eye on the weather forecast to make general decisions.

               Speaking of fertilizing, you expect a recipe with an exact dosage. 3 times a day, one teaspoon. 2 times 15 kg/dca. And do you know what's in your soil? Did you at least do a soil analysis here and there? And not the one about going through motions. But the real one. It's a major investment to get to know and improve your land. It's the beginning of consciously managed success. But here's where the Buts start piling up again. Relying on metrics is not an exact mathematical formula either. The earth is a complex entity. The interrelationships between the elements are complex. The ability of plants to assimilate elements varies and the behavior of mineral substances itself is very inconsistent depending on conditions, nothing that obeys patterns. We need to know the ability of the soil we farm to process, store and give up the basic food. This property has been formed over millions of years, and for this purpose you can rely on soil atlases and descriptions of Bulgarian soil types.

     The time has come colleagues for the return of Science of Agriculture. Those of us who examine, observe, analyze - not just memorize, but build upon - will succeed. It is very important to set fertiliser rates realistically, according to the specific situation, not only on the basis of theoretical knowledge. But they are important so that we can build our practice on them.

              Nitrogen feeding: the first question is - Are we looking for yield only, or quality as well. As an easy calculation technique we can use the following coefficients. We multiply these coefficients by the yield that our soil and our varieties have the potential to fulfil, and this gives our TOTAL nitrogen fertiliser requirement. For example, for bread wheat, from which we can get a yield of 900 kg/dca, the nitrogen requirement is 27 kg/dca To be clear - Premium wheat - it has another potential - 700. But the coefficient is 3,3. So the fertilizer requirement is 23 kg/dca. No more fertilizer needed for less yield. For 900 kg of barley - 22 kg/dca 

             Now come the next steps, the factors and conditions that reduce the need to the actual fertilizer rate: a/ What do we expect from nitrogen mobilization in the soil - that's why we need soil knowledge and analysis; b/ The legacy of the predecessor, c/ The uptake of the seed in autumn and d/ Its phase and condition at the threshold of the spring vegetation. These factors and values are deducted and finally we arrive at a rate of X kg/dca Nitrogen.

             You already know that a lot of mineral nitrogen cannot compensate for weak soil. This is where the soil mineralization and release factor comes in - on good soil it is higher, on weak and structureless soil it is lower. Next factor - precursor. After rapeseed you have an inheritance of 4-5 kg/dca of nitrogen, this is a saving on mineral fertiliser. After sunflower - 0 to 2 kg/dca legacy. Next we assess the condition of the crop - a tilled crop has absorbed and depleted more feed than a 3 leaf crop. Thus step by step we arrive at an economically and agronomically justified fertilizer rate, which we will divide into several doses. This is the job of your agronomist or consultant. Or your job - to research and calculate....

             After nitrogen in importance in early spring comes sulphur. It is also a very mobile element. In practice, it is of little importance to apply it in the autumn, when the initial development begins and the uptake of food by the plants is still weak. It does no harm, of course, but it should be emphasised in early spring. Sulphur is vital for protein building along with nitrogen. Proteins build the living organism. Therefore, in spring, when we supply a large amount of nitrogen, it is of great importance. And also - remember that sulphur has a very good fungicidal effect. Copper also has this effect. So if you saturate your cereal crops with sulphur and copper in the spring, you can also expect better vitality and plant health. I would like to clarify that sulphur is an essential nutrient, copper is a trace element, do not misinterpret the word saturation. It's just that the limit is different. The fungicidal effect is stronger in foliar treatments. You ask often - when sulfur - with the first or second dose of nitrogen. I would recommend with or close to the second if it is split.

              Next question: calcium and acid soils. My opinion is that calcium fertilizers are a quick-fix, but they are not the solution to the soil problem, nor to stable yields. You need to solve the problem long term. Soil liming is a costly exercise, but for your own land it is advisable - a must.

              Saturating the soil with organic matter is urgent, sensible and effective - a reminder about catch crops - a profitable option with multiple benefits. Besides being a source of food and structure for the soil, organic matter is also a balancer of soil reaction.

              Another important point in nutrition: what do you know about magnesium? Increasingly, we humans also drink it as a dietary supplement, but for plants magnesium is even more important as it enters the chlorophyll molecule. Chlorophyll directs photosynthesis, and it builds the plant organism, and that organism gives birth to your yield. A very important element. On any of your crops, you need to feed magnesium as foliar or part of the basal nutrition. It depends on the soil analysis. But even our black soils, the rich soils, often suffer from low magnesium availability. So provide for each crop, at the initial stage of the spring growing season - magnesium....

             The soil may have a supply of an element, but because of the soil reaction it is not available to plants.... there are also relationships between different elements, most often negative correlations, where because of the high content of one element, another cannot be assimilated into the plant. These are things that are critical to feeding your crops and converting fertilizer into yield. Here's a picture that's good to always remind yourself of. It doesn't show availability, your soil analysis will show that. It shows absorption. It shows that nitrogen, sulphur, potassium, magnesium and calcium are readily available at soil reactions from 5.5 upwards. BUT: you know - with a low soil reaction, if you decide to compensate with more sulphur, there is a danger that it will acidify the soil further. And unfortunately exactly the same applies to nitrogen. There we try to manoeuvre with different forms and compounds of it, but the yield of acid soils is limited, so remember economic profitability and don't hope for miracles. Such can happen if you conduct liming and work to increase organics.... with potassium and calcium on the contrary, compensation is possible and desirable.

Influence of pH-values on nutrient absorption


Phosphorus and boron - they are also quite delicate and capricious. They have a perimeter of optimum uptake in good neutral soil. Acidification sharply reduces their effectiveness, also at slightly above neutral reaction they "stretch" the plants and are unleashed again at stronger salinization.... general stock of most of our soils with phosphorus and boron is not brilliant, so these two elements want constant management.

I would like to remind you that elements like phosphorus and potassium are calculated over an entire rotation, not on a piece meal year to year basis, but that would be a topic for another lecture...

               Heavy metals - iron, zinc, copper and manganese - be careful with these! Very necessary as trace elements, but on acid soils they are highly mobile and you can over-saturate the crop if you overdo it. So far I have not actually seen anyone go overboard with trace elements apart from the zinc craze - I'm sure some of you have already got phytotoxicity from it. Things are complex.... there are also cases where the soil is oversaturated with iron, such are some of our grey and grey-brown soils. High iron content interferes with phosphorus uptake for example. So I say again and again and again - test your soils not only for basic substances, but also for trace elements.... other soils such as carbonate black soils conversely - the supply of metal trace elements is a must for a full yield. Each element has its importance in plant life and yield formation, but we must manage the crop and combine proper soil and foliar fertilization for maximum effect. Foliar is quick, inexpensive and very effective - as long as you choose quality products. It becomes even more relevant in the face of unheard of price hikes for mineral fertilisers.

             Very often you turn to specialists to diagnose by sight - a shortage of what is in your crops. Then it is already too late for compensation. Work preventively, with knowledge of the soil and the relationships within it... to improve soil properties structurally, humus content, acidity and more - the organic matter we provide to the soil is also important. Think living organics first and foremost -cover crops, your benefit will be long term as you will also revitalise the beneficial soil fauna through them, which in turn will help to renew the soil and feed the plants more fully.

Certified Agricultural Engineer Evelina Marinova
January 2022 г.