How to determine a reasonable fertilizer amount? A full breakdown of the scientific method
The determination of the fertilizer amount for walnut trees is based on the nutrient status of the soil and the nutrient requirements of the walnut tree. In addition, soil pH, topography, terrain, soil temperature and moisture, and soil management all affect the fertilizer amount and fertilization method. Determining a reasonable fertilizer amount means achieving both no excess and economical, effective use of fertilizer.
Pictured: walnut
To maintain the balance among the elements required by the tree, a reasonable fertilizer amount should be determined on the basis of nutrient diagnosis.
Reasonable amount of a certain element = (biological yield X average content of that nutrient in the plant - soil supply) ÷ utilization rate of the nutrient in the fertilizer
If the conditions for nutrient diagnosis are not available, the fertilizer amount can also be determined based on empirical values.
In China, based on the growth and development status of walnut trees, soil fertility, and different levels of cultivation and management, reference fertilizer amounts for early-bearing walnut and late-bearing walnut have been proposed. On soil of medium fertility, calculated by the area of the vertical projection of the tree canopy (or crown width), for late-bearing walnut from l to 5 years after planting, apply 50 grams of available nitrogen, 10 grams each of phosphorus and potassium per square meter per year; from 6 to 10 years, apply 50 grams of nitrogen and 20 grams each of phosphorus and potassium per square meter per year, and apply 5 kilograms of organic fertilizer (barnyard manure) per square meter per year; early-bearing walnut bears fruit early and consumes a large amount of nutrients, so the fertilizer amount should be greater than that of late-bearing walnut of the same age; from 1 to 10 years old, apply 50 grams of available nitrogen and 20 grams each of phosphorus and potassium per square meter per year, and 5 kilograms of organic fertilizer. For walnut trees 20 to 30 years old, the amount of organic fertilizer per tree is generally not less than 200 kilograms. If the soil conditions are poor, the tree growth is weak, and the yield is relatively high, the amount of base fertilizer should be appropriately increased. In areas with insufficient fertilizer sources, green manure can be widely planted and used.