Introduction inorganic fertilizers
Inorganic fertilizers (IF) have physical, chemical and physical-chemical properties that influence their quality. The term fertilizer is applied to any natural or manufactured material (with at least 5% of one or more macronutrients, such as: nitrogen, phosphorus or potassium) that is applied to the soil or plant to improve the supply of essential nutrients and promote growth. vegetable.
Manufactured fertilizers contain varying proportions of both macronutrients and micronutrients, impurities and other non-essential elements (eg heavy metals). This category includes inorganic fertilizers, organic fertilizers and soil conditioners (calcareous amendments), which can promote the growth of crops or pastures by increasing the availability of essential nutrients in the soil or by improving the physical structure of the soil.
The sources of essential nutrients, for crops or grasslands, can come from inorganic fertilizers or organic fertilizers. Inorganic fertilizers (also called commercial, synthetic, or artificial fertilizers) contain chemicals with essential nutrients in forms available to plants, the production of which has involved some industrial process. Instead, organic fertilizers contain carbon-based organic material from animal and plant products.
Properties of inorganic fertilizers
Inorganic fertilizers (IF) have physical, chemical and physical-chemical properties (Figure 1) that influence their quality and that producers and advisors must know before selecting the type of fertilizer to buy.
1. Physical state: the presentation of the IF can be liquid or solid, which determines its use and effectiveness. Solid IFs can come in different types (Figure 2), such as powders (with a larger reaction surface with the soil, easily assimilated by plants and with loss problems during transport, handling and distribution by mechanical systems applied in the field) , crystals, granules or pearls (easy to handle and uniformly distributed in the field by mechanical systems, in the case of granules and pearls, up to 2% powder is accepted).
2. Granulometry: corresponds to the size and proportion of particles in the total volume of the fertilizer. Particle size affects agronomic response, mixing, storage, fertilizer handling and application properties. In Chile, there is no current regulation for this parameter.
The particle size distribution is determined by sieving. The granulometric analysis (Vistoso et al., 2017) of diammonium phosphate and triple superphosphate indicated that particles > 2 mm corresponded to 91-96% and 70-97%, respectively, of the analyzed samples.
Fertilizers with variable size particles tend to segregate, being relevant in the preparation of physical mixtures and in the handling of bulk fertilizer.
Chemical properties of inorganic fertilizers
1. Grade: indicates the percentage of primary nutrients (N%:P%:K%:S%) per dry weight unit of the fertilizer, expressed as N:P2 O5 :K2 O:S.
The term percentage (%) means “out of one hundred”, so in the analysis or label 8.5% means 8.5 out of one hundred and 45% means 45 out of one hundred. For example: 100 kg of Triple Superphosphate with a nutrient analysis or label value of 0:45:0:10 will contain 0 kg N, 45 kg P2O5, 0 kg K2O and 10 kg S.
Therefore, the amount of nutrients in 1 Mg (1,000 kg) of a fertilizer will be ten times the amount of nutrients in 100 kg. So 1 Mg of Triple Superphosphate with a nutrient analysis or labeling of 0:45:0:10 will contain 0 kg N, 450 kg P2O5, 0 kg K2O and 100 kg S.
In a study conducted by INIA, the P2O5 concentrations of monoammonium phosphate, diammonium phosphate, triple superphosphate and rock phosphate fluctuated between 28-62%, 28-49%, 40-56% and 14-30%, respectively, in relation to , at its standard concentration (Vistoso et al., 2017).
Fertilizers applied to the soil must comply with national regulations, in relation to their properties. Therefore, it is relevant that producers and technical advisors verify the composition of the fertilizer to be used through its chemical analysis.
2. Fertilizer reaction in the soil: indicates the magnitude of the acidifying and/or alkalinizing effect of the inorganic fertilizer on soil pH, which is expressed as acidity indices (kg CaCO3 that neutralize the acidification of 1 kg N or 100 kg fertilizer) and alkalinity (kg CaCO3 similar to alkalinization of 1 kg N or 100 kg fertilizer). Both allow us to select the fertilizer, time and form of application in order to maximize the efficiency of nutrient use.
1. Solubility: indicates the amount of fertilizer that dissolves in 100 g of water at 25 ºC and, therefore, the proportion of the nutrient available to the plant. At INIA, methodologies were implemented and validated to determine the solubility in fertilizers that presented high accuracy and precision.
The solubility indices in water (P2 O5 available to plants) of monoammonium phosphate, diammonium phosphate and triple superphosphate fluctuated between 100%, 95-100% and 66-100%, respectively (Vistoso et al., 2017). This indicates that soluble phosphorus fertilizers are not 100% soluble and the dose of P2 O5 must be adjusted, especially in the fertilization of annual crops, increasing the cost ha-1.
2. Hygroscopicity: this indicates the behavior of the fertilizer when absorbing water from the air at a certain relative humidity (Table 1), which varies with temperature.
This process damages the physical structure, by dissolving particles (soft and sticky) and, subsequently, by drying out again; clods (caking) are generated that hinder the displacement of the fertilizer granules in the mechanical distribution systems and; therefore, it affects the uniformity of application in the field (Figure 3).
Therefore, it is relevant to consider adequate conditions during storage (temperature, relative humidity) and application of IF (rainfall).
3. Salt index: is a measure of the concentration of salts that the fertilizer generates in the soil solution, expressed as the ratio of the increase in the osmotic pressure of the saline solution generated by a fertilizer with respect to the osmotic pressure of the same amount of sodium nitrate ( relative value= 100).
Its importance lies in the fact that fertilizers with a lower index (Table 2) are less phytotoxic in applications together with or near the seed; being relevant in the planting of crops or establishment of meadows.
Fertilizer Application Methods
Application methods for solid or liquid sources are as follows:
Surface Applications: associated with pre-sowing applications, in post-emergence with the crop in development and with irrigation water. 1. Pre-sowing or post-emergence broadcast. 2. Pre-sowing, sowing or post-emergence in strips on the ground. 3. Post-emergence with irrigation water.
Sub-surface applications: fertilizer applications along or near the seeds and roots can generate phytotoxic effects; due to the saline effect discussed in the previous point.
1. Al voleo and incorporado with rastra or disk.
2. In bands with the seed or to the side and below the seed.
3. In deep bands.
4. In bands on the side of post-emergence plants.
5. On the plants: spray on the foliage of the crop (foliar).
Broadcast applications are common for mobile essential nutrients such as N. In contrast, low-mobility nutrients (such as P) are applied in bands incorporated with or near the seed to maximize subsequent root-essential nutrient contact.
Final considerations on inorganic fertilizers
– Fertilizers contain essential nutrients and play an important role in agricultural production and influence the nutritional quality of food.
– Sources of essential nutrients can be inorganic or organic.
– Fertilizers should be purchased based on their nutrient analysis or label values and their ability to overcome a paddock-specific essential nutrient deficiency; which has been determined through soil analysis.
– When making fertilizer recommendations, it is important to use the amount of fertilizer per hectare. (Example: 100 kg ha-1 of urea). Also, keep amounts rounded to the nearest “0” or “5”. (Ex: 10 kg ha-1 or 25 kg ha-1, not 14.3 kg ha-1).
– The contribution of essential nutrients to crops and meadows must be balanced and friendly to the environment; in post to achieve an efficient and responsible use of fertilizers.