Chapter 5. Fertilizer use recommendations and balanced fertilization

Fertilizer use recommendations

Fertilizer recommendations for the major crops in selected provinces are shown in Table 15.

Some crop growers use higher levels of potassium, sulphur and micronutrients compared with the SWRI recommendations.

TABLE 15
SWRI's fertilizer recommendations of the major crops by province

Balanced fertilization

The increased mineral fertilizer consumption in Iran during the 1980s and the first half of the 1990s brought with it an unbalanced use of primary nutrients. Phosphorus application rates were in excess of crop needs, resulting in the accumulation of phosphorus in major farming areas and causing the precipitation of certain micronutrients present in the soil, especially zinc and iron. The application rates of potash plus quantities released from the soil were lower than plant uptake requirements. Micronutrients were rarely applied. An improvement in the nutrient balance since the mid-1990s is indicated in Tables 16 and 17.

TABLE 16
Trends of fertilizer use and fertilizer use ratios

The fertilizer use efficiency (FUE) is based on two assumptions a) fertilizers produced 50 percent more yield in comparison with control plots and b) yield concerns only the grain and edible parts of the products. It is also calculated based on the papers of Raun and Johnson (1999). The FUE is higher in some parts of the country than in others. It is assumed that this is mainly due to a higher soil organic matter content or the optimal use of organic fertilizers, especially manure.

TABLE 17
Relationship between rainfall, fertilizer use, nutrient ratios and agricultural production

1 FUE = fertilizer use efficiency

The figures in Table 17 indicate that rainfall has had a major impact on production. The same is probably true of improvements in other crop production practices. Crop yields have increased by more than 20 percent on average. The improvement in the nutrient balance is partly due to the implementation of fertilizer recommendations based on soil tests. Fifty soil-testing laboratories have been established.

The fertilizer use ratio of nitrogen (N), phosphorus (P₂O₅), potassium (K₂O), and micronutrients is targeted to improve to 100-50-40+4 percent micronutrients in 2010 provided that the materials are available for application and in time (Malakouti, 1996; Bybordi et al., 2000; Malakouti, et al., 2001 and 2004). A balanced application of fertilizers could improve the production levels by up to 60 percent (Malakouti; 1996; Harris, 1998; Hamdallah, 2000; Roy, 2001; Balali et al., 2003; Malakouti et al., 2004).