Best practice in fertilizer use

The amount of plant nutrients to be applied to the soil in the form of fertilizers has to be determined each year to ensure that it matches the nutrient requirements of the crop. Manures are by-products in agriculture and have to be used if available. To obtain maximum profit a farmer has to apply the optimum fertilizer rate, which usually changes from field to field and from year to year. A mineral fertilizer recommendation to establish the optimum fertilizer rate can be calculated according to the following principle:

Nutrient demand of the crop
-  Nutrient supply of the soil
-   Nutrient supply from farm manure and crop residues
= Mineral fertilizer demand

• The nutrient demand of a crop can be estimated by recommendations obtained from field experiments considering the variety, expected yield, nutrient content and local soil and weather conditions. Crop yield multiplied by the nutrient content of a crop gives the nutrient uptake.
  
  
• The nutrient supply from the soil consists of two components:
  • Mineral nutrient content at the beginning of the cropping period, which can either be measured or estimated based on knowledge of soil type, previous crop and local weather conditions.
  • Nutrients released from the decomposition of soil organic matter during crop growth. Fertilizer recommendations should estimate the nutrient supply from different soil types during crop growth. However, the weather during the growing season will create substantial annual variation in the mineralization rate.
    
• Farm manures, if available, should be combined with mineral fertilizers. However, the nutrient content of manures usually varies with collection and storage methods, feed composition and type of animal. It should also be considered that part of the nitrogen in farm manure is not available to the crop during growing season.
  

Decision support tools from Yara
Correct timing of fertilizer application is important for optimum plant nutrition. The right time to fertilize is close to the time of nutrient uptake by the crop. A NPK fertilizer application in spring ensures a good start of crop growth. Later in the season split dressings allow growers to adjust the fertilizer application to the physiological development in the different growth stages of the crop.

Yara has developed a range of tools that assist farmers in their decision about the right fertilizer product and the optimum fertilizer rate and timing:

• Fertilizer recommendation software, which gives guidance on correct application rates and timing of fertilizers (YaraPlan, Nplan, ExtranPlan).
  
  

The Yara N-Tester measures the nutritional status of crops during growth by analysing the chlorophyll content of the leaves, which is closely related to the nitrogen nutrition status of a crop.

Precision farming, also known as site-specific fertilization, is a management strategy that addresses within-field variability. The Yara N-Sensor optimizes fertilizer inputs on a point-by-point basis within a field. By reducing over-application and under-application of nitrogen, this strategy improves profitability for the farmer and also reduces the threat to groundwater pollution from fertilizers

Many growers from all over the world confirm that decision support tools from Yara have proven to be effective and of high value. Recommendation from Yara ensures that they use a high quality fertilizer at the right time and the right rate. Thus the crop will grow to a high yield in a good quality.