Soil Fertility Definition
Soil fertility is the ability of a soil as an environment for plant growth to support plant growth by supplying necessary plant nutrients and desirable chemical, physical, and biological characteristics. Plant nutrients include nitrogen, phosphorus and potassium, sulfur, calcium and magnesium macronutrients.
Boron, chlorine, copper, iron, manganese, molybdenum, and zinc are basically micronutrients. Fertilizers are chemical or natural compounds or products used in rice schemes, fertigation or hydroponics, or aquaculture operations to provide nutrients to plants, typically by application to the soil, but also to the leaves or water. Chemical and mineral fertilizer requires nutritional sources.
Importance of Soil Fertility
One of the important factors having a significant effect on crop yield and quality is soil fertility and nutrient conservation. Regardless of the scale of the field or plot, the secret to a good vegetable production enterprise is to supply plants with the right amount of nutrients at the right time.
To achieve this goal, the first step is to track the levels of soil nutrients by annual soil tests. Per year, collecting and administering soil samples in the spring or fall (preferred) serves as a soil report card. Soil test results assist in the assessment of soil organic matter, pH, electrical conductivity, ability of cation exchange, and essential macro levels (phosphorus, potassium, magnesium, calcium) and micronutrients (boron, zinc, etc.).
These reports also assist in calculating application amounts of lime or sulfur to increase or decrease soil pH, respectively. For most crop rotations, which involve vegetable crops, maintaining a soil pH between 6.0 and 7.0 is advised. In that range, a good number of vegetables grow well, since most of the nutrients are readily available.
Crops such as asparagus, brassica, garlic, onions, and spinach are low pH susceptible crops that need above 6.5 pH maintenance. The secret to holding a safe and efficient vegetable production enterprise is the maintenance of optimal soil nutrient levels. It is necessary to know the cultivation and soil fertilization history of the field before a fertilization program can be scheduled.
Knowledge thus gleaned gives a strong base for potential projects for nutrient conservation. Management aspects of certain primary nutrients are provided below:
- Nitrogen: In vegetable processing processes, nitrogen is one of the most essential nutrients to be handled. Nitrogen is readily leached, can volatilize if not rapidly incorporated, and soil microorganisms can immobilize it. Since nitrogen can easily be measured across many mechanisms, nitrogen is not regularly tested to make crop recommendations by soil testing laboratories.
Recommendations for nitrogen instead are based on quantities of soil organic matter. Nitrogen implementation timings, application processes, and sources are equally relevant in addition to the number. Synthetic and organic fertilizers and leguminous cover crops such as hairy vetch, red clover, crimson clover, cowpea, soybean, etc., which fix atmospheric nitrogen, provide sources of nitrogen fertilizers.
Synthetic fertilizers widely used contain urea, ammonium sulfate, calcium and potassium nitrate, and ammonium nitrate urea. Compost, aged compost, rock phosphate, soybean meal, and fish meal are the organic nutrient sources.
- Phosphorus: For plant growth, adequate phosphorus is necessary. While phosphorus is needed in lower quantities than other major nutrients, it is important during the growing season in the early developmental phases of growth and in the energy transition within the plant.
Vegetable crops grown in a deficient or below ideal phosphorus level measuring soil significantly benefit from the application of phosphorus and indicate a positive response to Phosphorus fertilizer additions. Optimal soil test crops may or may not react to further additions, but Phosphorus may be used to preserve the degree of fertility in the optimum range (Phosphorus fertilizer applied at crop removal rates).
It is important to balance the need for Phosphorus in crops with the environmental risk of getting too much Phosphorus in the soil. Via soil erosion, surface runoff, or tile irrigation water, phosphorus lost from the field and dumped into surface water may cause algal blooms and kill fish.
Via yearly soil samples, it is also important to track and change phosphorus use. In order to sustain soil test Phosphorus at the optimum level, in addition to the use of soil tests, the input amount of Phosphorus fertilizer should be roughly equal to the rate of Phosphorus extracted from harvest.
- Potassium: Potassium is used by plants in concentrations nearly equal to or marginally greater than nitrogen. Potassium directly affects many essential physiological pathways, such as photosynthesis, carbohydrate transport, and water regulation.
The maintenance of optimal soil and plant potassium levels contributes to improved resistance to disease, increased tolerance to drought, and vigorous vegetative growth. As a result, potassium fertilization is also associated with increased production of crops as well as healthier properties for processing and storing.
Plants that are potassium deficient are stunted and weak root systems grow. Where the soil test shows that K is deficient or below optimum, crops are very likely to react to K fertilizer. Bad fruit quality (internal whitening, incomplete maturation, etc.) in tomatoes is also associated with potassium deficiency. Potassum nitrate, potassium sulfate and potassium chloride are natural sources of potassium.
- Calcium: In plant leaves, calcium, a structural part of plant cell walls, is most abundant. In those soils where excessive potash fertilizer has been applied and/or where crops are subject to drought stress, calcium may be deficient. Deficiency of calcium results in badly formed root systems and comparatively few poor-quality fruit.
Blossom end rot of tomatoes and pepper is one of the classic examples where fruits grow a water-soaked area on or near the blossom end of the fruit that later darkens and enlarges in a continuously widening circle before the fruit starts to mature. It is caused by a deficiency of calcium in the growing fruit, which may be attributed to a lack of soil calcium absorption or to significant water supply variability.
A soil pH above 6 is needed by most vegetable cropping systems, which is accomplished by regularly adding lime, which in turn supplies calcium. A strong source of lime is calcitic limestone or aglyme. Some sources contain sulfate of calcium (gypsum), and nitrate of calcium.
- Magnesium: Magnesium is an essential chlorophyll component and thus plays a vital role in photosynthesis. Magnesium defects in vegetable crops are observed as interveinal chlorosis on mature bottom leaves. In soils that are deficient in magnesium and where there is a need to improve soil pH, dolomitic or high-magnesium limestone is typically used. Magnesium may be added as a foliar spray (Epsom salt) to supply the crop with magnesium in critical circumstances. Magnesium is also provided by renewable sources such as soil, waste, and most organic fertilizers.
- Sulfur: Sulfur is an essential nutrient for plants, especially those of the onion and cole plant family (broccoli, cabbage, and cauliflower). In high pH soils, elemental sulfur application not only decreases soil pH, but also provides sulfur. Sulfur may also be provided by the application of nitrogen fertilizers containing sulfur, gypsum or Epsom salts. Application values for sulfur are dependent on the absorption of crop S. When soil sulfur levels are higher than 20 ppm, sulfur fertilization is typically advised.
- Micronutrients: Micronutrients are needed in very limited amounts, as the name implies, and distributed in plant tissue as parts per million (ppm). Boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc are included, respectively (Zn). Cobalt (Co), silicon (Si), sodium (Na), and vanadium are other trace elements that some but not all plants need (V). Micronutrients, while necessary in very limited quantities, have an important role to play in plant growth and production. Most of them are involved in enzymatic reactions that, including photosynthesis and respiration, are important for plant survival. It is advisable to test for micronutrients before checking the soil for the first time. Test for micronutrients every 4 to 5 years after initial concentrations are established and steps have been taken to maximize them.
In several of the Sustainable Development Goals, the consequences of soil fertility are expressed, as they cover fiscal, social and environmental aspects. The key role of fertile soil is the supply of food, which is very important given the Zero Hunger target of FAO.
Fertile soil also contains vital nutrients for plant growth, supplying all the necessary nutrients necessary for human health to produce nutritious foods. In addition, fertility has an impact on high-impact practices and is thus connected to economic prosperity and the fight against poverty.
Finally, effective soil fertility management will help mitigate soil, water and air contamination and control water resources. The innate potential of the soil to provide plant nutrients in ample quantity and adequate proportion & free from harmful pollutants is soil fertility. The ability of the soil to grow crop / unit area is soil productivity.
Therefore, based on crops, marketing status & several other considerations (excessive acidity / alkalinity, prevalence of harmful compounds, poor physical properties or water deficiency), fertile soil could or could not be active. Every viable soil, however, must be fertile. Generally, soil production depends to a large degree on soil fertility.
Types of Soil Fertility
- Intrinsic / Natural Fertility: Soil produces certain minerals in nature that are considered ‘inherent fertility’. Nitrogen, phosphorus & potassium are required among the plant nutrients for normal growth as well as crop yield. India’s soil contains 0.3 – 0.2% nitrogen, 0.03 -0.3% phosphorus & 0.4 -0.5% potassium. Natural reproduction is a limiting element but does not minimize fertility.
- Acquired Fertility: ‘Acquired fertility’ is the fertility produced through the use of manures & fertilizers, tillage, irrigation etc. There is also a limiting factor in acquired fertility. The experiment shows that the yield is not significantly improved by the application of extra fertilizer amounts. It is therefore important to add fertilizer on the basis of a soil’s nutrient content and to estimate it by soil testing.