3 key variables before a fertilization program

Introduction

Ecological fertilization has established itself as a key strategy for improving agricultural productivity in a sustainable manner. However, its success depends not only on product quality but also on a prior analysis of certain variables that determine program efficiency. In this article, we explore the three key variables that every farmer or technical advisor must evaluate before implementing an ecological fertilization program in 2026. Knowing the soil's condition, the crop's needs, and the climatic conditions allows for designing a precise nutritional strategy, reducing costs and maximizing results. At Ecoganic, we develop science-based biostimulants and ecological fertilizers, adapted to the demands of modern agriculture.

Variable 1: Soil analysis and its current fertility

The first step for any ecological fertilization program is to thoroughly understand the soil where the crop will be grown. A complete soil analysis reveals essential parameters such as pH, organic matter, cation exchange capacity (CEC), available macro and micronutrients, and biological activity. This information allows for adjusting the doses and types of ecological fertilizers, avoiding unnecessary applications or hidden deficiencies.

Critical parameters to measure

• Soil pH: Influences nutrient availability. Most crops prefer a pH between 6.0 and 7.5. Outside this range, certain nutrients become locked up.
• Organic matter: It is the foundation of natural fertility. A low content indicates a need for prior organic amendments.
• Available nutrients: Nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and micronutrients such as zinc, boron, and iron.
• Biological activity: The presence of beneficial microorganisms is key for nutrient mineralization. A biologically active soil responds better to ecological fertilizers.

Conducting a soil analysis at least 30 days before the program starts allows for informed decision-making. At Ecoganic, we offer technical advisory services to interpret these results and design a customized fertilization plan.

Advanced interpretation of soil analysis results

Beyond absolute values, it is crucial to interpret nutrient relationships. For example, the ideal carbon-to-nitrogen (C:N) ratio for agricultural soils ranges between 10:1 and 15:1; values above 20:1 indicate nitrogen immobilization by microorganisms, requiring additional organic nitrogen applications. The calcium-to-magnesium ratio should be maintained between 3:1 and 7:1 to avoid compaction or induced deficiencies. A potassium-magnesium imbalance can cause magnesium blockage if potassium exceeds 5% of the CEC. In soils with a CEC below 10 cmol/kg, applying amendments such as zeolites or bentonite is recommended to improve nutrient retention. Recent studies at Wageningen University showed that adjusting these ratios can increase organic fertilizer efficiency by 25-30%.

Sampling methodologies and recommended frequency

Sampling should be done in a zigzag pattern, taking 15 to 20 subsamples per hectare at a depth of 0-30 cm for annual crops and 0-60 cm for perennials. It is recommended to avoid areas with recent fertilizer or manure residues. The ideal frequency is annual for intensive crops and every 2-3 years for extensive systems. In sandy soils with low buffering capacity, pH can vary by up to 0.5 units in one season, so semi-annual monitoring is suggested. The use of apparent electrical conductivity (ECa) sensors allows mapping of soil spatial variability, identifying areas with different fertilization needs. This technique, combined with laboratory analysis, reduces sampling costs by 40% and improves the accuracy of recommendations.

Biological indicators of soil health

Basal microbial respiration (mg CO2/kg soil/hour) is a key indicator of biological activity; values below 0.5 indicate low nutrient mineralization. Microbial biomass (measured as microbial carbon) should represent at least 2-5% of total organic carbon. The ideal fungi-to-bacteria ratio for agricultural soils is 1:1 to 1:3; excessive bacterial dominance suggests anaerobic conditions or excess nitrogen fertilization. Tests such as the nitrogen mineralization test (potentially mineralizable nitrogen) predict organic nitrogen release during the season; values above 40 mg N/kg indicate high supply capacity. In soils with low biological activity, the application of arbuscular mycorrhizae (Glomus spp.) can increase phosphorus uptake by 60% and improve tolerance to water stress. Ecoganic offers biostimulants that include selected microbial consortia to enhance these indicators.

Practical example: Correcting deficiencies in calcareous soils

In a citrus crop in the Murcia Region, soil analysis revealed pH 8.2, CEC 12 cmol/kg, organic matter 1.2%, and zinc (0.3 ppm DTPA) and iron (2.1 ppm DTPA) deficiencies. To correct iron chlorosis, EDDHA iron chelate (6% Fe) was applied at 3 kg/ha via fertigation, combined with humic acids (5 L/ha) to improve chelation. The zinc deficiency was treated with zinc sulfate monohydrate (35% Zn) at 2 kg/ha in two foliar applications during vegetative growth. Olive pomace compost (10 t/ha) was incorporated to increase organic matter to 2% over three years. The program included biostimulants with phosphorus-solubilizing bacteria (Bacillus megaterium) to improve phosphorus availability, which was at medium levels (12 ppm Olsen). After 18 months, production increased by 22% and chlorosis symptoms were reduced by 80%.

Variable 2: Specific crop needs and phenology

Each crop has distinct nutritional requirements, and these vary throughout its phenological cycle. An organic fertilization program must be adjusted to the development stages: germination, vegetative growth, flowering, fruit set, and ripening. For example, broadleaf crops demand more nitrogen in early stages, while fruit trees require potassium and phosphorus during fruit formation.

Organic fertilization according to the crop

Organic fertilizers, such as Ecoganic biostimulants, are formulated to release nutrients gradually, synchronized with crop demand. However, it is crucial to know the nutrient extraction per ton of harvested product. For example, a tomato crop extracts approximately 2.5 kg of N, 0.5 kg of P, and 3.5 kg of K per ton. These values guide the application rates.

Furthermore, the presence of abiotic stress (drought, salinity, extreme temperatures) can alter nutrient uptake. In such cases, the use of biostimulants that improve stress tolerance, such as those we develop at Ecoganic, enhances the program's efficiency.

Detailed nutritional requirements by crop

For extensive crops such as wheat, extraction per ton of grain is 25 kg N, 10 kg P2O5, and 20 kg K2O, with a harvest index of 50%. In corn, requirements are higher: 30 kg N, 12 kg P2O5, and 25 kg K2O per ton, with nitrogen uptake peaks during grain filling. In olive groves, extraction per ton of olives is 12 kg N, 3 kg P2O5, and 15 kg K2O, but potassium is critical for oil quality. In vineyards, the N:K ratio should be 1:1.5 during veraison to avoid imbalances affecting sugar accumulation. Studies from the Institute of Agricultural and Fisheries Research and Training (IFAPA) show that organic fertilization with grape pomace compost can cover 60% of potassium needs in vineyards, reducing the application of mineral fertilizers.

Phenology and synchronization of nutrient release

Nitrogen release from organic sources such as compost follows an exponential curve: 30% is mineralized in the first 30 days, 50% in 60 days, and the remaining 20% in 90-120 days, depending on temperature and moisture. For short-cycle crops like lettuce (60 days), it is recommended to use fast-mineralizing organic fertilizers (blood meal, 13% N) combined with mature compost. In perennial crops like almond trees, nitrogen demand is highest during shoot growth (March-May) and fruit set (June-July). The application of green manures (vetch, 150 kg N/ha) in autumn synchronizes nitrogen release with vegetative awakening in spring. The use of bio

References

• National Institute of Statistics
• Official State Gazette