Long-term soil tests to evaluate soil fertility management methods

The importantroleof soil fertility in food production warrants long-term monitoring to track changes in soil properties. Long-term soil tests are field trials conducted onpermanent plots that are regularly sampled to quantify soil changes over time scales of decades. This article intends to introducelong-term soil fertility testsusing permanent plots aimed atcollecting information on the effects of long-term soil fertility management practices on soil properties. Efforts are also made to develop a general methodologyfor future research. Mosttests on permanent plots in the past mainly focused on soil carbon concentrations over long-term periods to find that continuous applicationof organic matter toarable land led not only to improved soil physical and chemical properties but also toits enhanced biological activity.This is while organic modifiers, especially when improperly applied,may reportedly contributeto environmental pollution. So far few long-term soil tests have been conducted in Iran,most of which havemainly determinedthe residual effects of fertilizers containing single nutrient elements such asphosphorus, zinc, orpotassium. This lack of consistent tests and the scant information thus far obtained necessitate planningfor drastic and targetedtestson Iranian soils.Evaluation of long-term experiments revealed that it will be necessary to employsuch variedland management practicesof livestock manuring, proper crop rotation, and avoidance of severe tillage to enhancecarbon sequestration in soils. Finally, it was observed that the use of chemical fertilizers combined with organic and biological agentsis favorable to increased agricultural production and enhanced sustainable soil fertility.