Is the wheat hungry? When and how much to fertilize?
You can get answers to these questions by the Meteobot® Nitro precision fertilizing system. It takes into account the most important factors, affecting nitrogen uptake and respectively – the yield and grain quality:
Soil type and contents
On this basis, the system gives recommendations about the amount of nitrogen that is necessary to achieve the planned yield and grain quality with the minimum possible cost for nitrogen fertilizers.
How does that happen in practice?
On the following charts are displayed the average yields and protein content from field trials conducted in 2018/2019. It is clear, that in order to achieve bread wheat quality (and respectively – a higher sales price), in this specific case a minimum of 100 kg active substance of nitrogen per hectare has been necessary.
What is Meteobot® Nitro?
Meteobot® Nitro consists of several components:
Satellite monitoring of crops
Crops’ development during the growing season is monitored on satellite pictures. Using the NDVI vegetation index, the good, average and poorly developed zones in the field get outlined.
Chlorophyll content measurement
The chlorophyll in a plant’s leaf corresponds directly to nitrogen uptake. By measuring chlorophyll, you get information how much nitrogen has the plant taken up by now. The measurement is made before nitrogen application. We recommend one measurement for each zone, identified on the satellite pictures.
Meteobot® Micro compact weather station
The weather station measures rain, soil moisture and soil temperature, and sends data about that in real time. The data is stored and aggregated from the date of seeding up to the current moment. Besides, Meteobot® Micro provides a local weather forecast for the location where it is installed.
It contains data about soil type (clay, sand, silt) and respectively – the soil’s ability to retain moisture and nutrients, risk of nitrogen leakage, etc. Next to that you get data about pH, organic matter, availability of sulphur, phosphorous, potassium, and microelements, which directly affect nitrogen uptake and hence – the yield.
On the basis of chlorophyll content, rainfall, soil moisture, temperature, soil type and content, weather forecast and wheat variety, we provide a customized fertilizer recommendation.
Well developing crops take up more nitrogen, have higher chlorophyll content, and produce greater yields. Chlorophyll measurement shows how much nitrogen have the plants taken up, and how much more they need to achieve their maximum yield potential.
The measurement is made with an optical chlorophyll-meter – directly in the field. It is not necessary to pick leaves and send them to a laboratory for chemical analysis. The measurement is carried out right before fertilizer application. This way you get the most accurate information how much nitrogen to apply.
Rainfall and Temperature – When to Fertilize?
The main factors, which influence nitrogen uptake (and hence – the yield), are rainfall and temperature. If there is no moisture, plants cannot take up the available nitrogen from the soil. Similarly, if the temperature is low (below 5°C), the vegetation process stops and plants cannot take up nutrients.
Nitrogen uptake is not constant in time. Wheat needs most nitrogen when it grows fast in the end of tillering and during stem elongation. However, nitrogen has to be applied only if soil moisture is enough, or if adequate rainfall is expected. Otherwise, there is a risk of nitrogen loss or of grain shrinking during grain filling. That is why it is very important to monitor soil moisture, forecasted rain and actual rainfall.
If there is enough rainfall, it is wise to apply more nitrogen for a higher yield. Alternatively, if the soil is dry, it is better not to apply nitrogen until an adequate rainfall is forecasted.
You get all of this information from the compact Meteobot® Micro weather station – directly on your smartphone. The small size and the built-in GPS for security and tracking make it possible to install Meteobot® Micro in the field.
Meteobot® Micro sends real-time data about rain, soil moisture and soil temperature. Moreover, you get a local weather forecast for 10 days ahead for the location of the weather station.
If the field crop is uniform, it is enough to measure chlorophyll at a single location. If there are non-uniform zones, it is necessary to make one measurement in each zone. How to differentiate zones? This is easiest to do on satellite images – for example in Onesoil or At.farm.
As you can see on the picture, there are three main zones in this field – well developed (dark green), moderately developed (green) and under-developed (light green). In this it is necessary to make three chlorophyll measurements – one in each zone. This way you will know what rate to apply in each zone. In this particular case, for example, it is recommended to apply 40 kg N/ha in the well developed zone, 60 kg N/ha in the moderately developed one and 80 kg N/ha in the under-developed zone.
If you are going to apply a fixed rate, you can take the average for the whole field.
It is possible, of course, to apply a variable rate.
Variable Rate Fertilizing
This is very easy to do – just enter the application rates for each zone in the satellite imagery software. It automatically creates a variable application map. You can download it as a file on a USB flash drive and load it in the GPS navigation system of your tractor – e.g. Trimble, Amazone, Raven, Ag Leader, John Deere, Topcon, etc.
Variable Application Strategies
There are two main strategies for variable fertilizing. With the first, the so-called “socialist”, one more fertilizer is applied on weaker zones and less – on stronger zones. This strategy is suitable for the beginning of the season – when weaker zones have enough time to catch up with stronger ones. The effect of this strategy is that you get a more homogenous yield throughout the field. This leads to fewer losses during harvesting, because it is not necessary to change combine settings abruptly between zones.
However, there is something you need to consider with this strategy. According to field studies by Onesoil, if you apply more fertilizer to weaker zones, in 55% of the cases you will not get a higher yield. The reason is that nitrogen is often not the limiting factor, but, for example, acidic soil (low pH), uneven terrain (quick to drain or flood), lack of other nutrients and so on. In order for the “socialist” strategy to work, you need to find out which is the problem and solve it, if possible. If you cannot solve it, there is no point in applying more nitrogen to weaker zones – this will only lead to greater losses.
The other strategy is the so-called “capitalistic”. With it you apply more fertilizer on stronger zones and less – on weaker ones. This strategy is usually applied in the end of the growing season, when weaker plants will anyway not have enough time to take up more fertilizer. The effect of this strategy is that you get the maximum yield potential from stronger zones.
Soil Analysis – Are There Any Limiting Factors?
The effect of nitrogen fertilizing depends on the type and chemical composition of soil too. For example, even if we apply a lot of nitrogen, it will not be used efficiently, if the value of pH is low (acidic soil), if there are not enough carbon (organic matter) and microelements. Similarly, if the soil is sandy and there is a lot of rainfall, nitrogen leaches and plants remain hungry. Due to these and other factors, we have seen cases where 400 kg/ha active substance of nitrogen has been applied (while usually 170-200 kg/ha) without a significant yield increase.
That is why, in order to achieve the maximum effect of nitrogen application, we recommend soil analysis for:
Soil type (clay, sandy, silt);
Ability to retain nutrients (cation exchange capacity);
Nitrogen leaching risk;
Organic matter (humus);
Available phosphorous and potassium;
Available sulphur and other microelements.
Every farmer knows their fields. It is usually not necessary to take 50 samples to find out that there are 2 or 3 soil zones in your field. This is expensive and inefficient. Besides, soil mapping is not particularly suitable for nitrogen fertilizing. Nitrogen is very mobile in soil – if you make soil analysis before seeding, part of the available quantity is very likely to get lost before the crop is able to use it.
That is why we use soil analysis to find out whether there are any yield limiting factors. If you remove those factors (e.g. apply sulphur fertilizer, or lime to increase pH, or incorporate residues after harvest to increase organic matter, etc.), you can get the full effect of nitrogen fertilizing.
The nitrogen recommendations from Meteobot® Nitro take into account wheat varieties. As you may know, some varieties are visibly greener (i.e. they have more chlorophyll), but this does not necessarily mean, that they produce higher yields. To take into account these specifics, we carried out field trials with many wheat varieties at different locations. This way we developed precise fertilizing algorithms for the tested varieties, and a universal algorithm for other varieties.
What is the result?
You can see the cost calculation of the Meteobot® Nitro fertilizing in the following table:
* Prices are for bread wheat FOB Black Sea as of July 5th, 2019