Sensitivity of Plant and Soil Indices in Evaluating the Long-Term Consequences of Soil Mining from Reserves of Phosphorus, Potassium, and Magnesium

Abstract

Mineral fertilizer production and distribution in Poland prior to 1991 were subsidized by the state. Demand for low-cost products exceeded substantially their production. During the transformation to market-oriented economy, the subsidy on fertilizers was removed and the demand from agriculture dropped dramatically. In 2008/2009 mineral fertilizer consumption reached only 122 kg nitrogen–phosphorus–potassium (N–P–K) per 1 ha and the N/P/K ratio remained 1:0.3:0.4. This tendency is disturbing because the soils in Poland are commonly acidic and poor in available K and Mg. Nitrogen fertilization and high-yielding crops compound the process of soil depletion. The objective of this article was an evaluation of soil and plant index sensitivity for soil exhaustion from P, K, and Mg. Two factorial experiments were carried on in 2003–2009 in a four-crop rotation: winter rape–winter wheat–maize–spring barley. The first factor was treatment without P, K, or Mg and a control treatment fertilized with all the macronutrients and the second one had five levels of N. For determination of plant fertilizer recommendations, official methods have been used (Egner DL, Schachtschabel). The nutrient requirements of crops were evaluated by determining the concentrations of N, P, K, and Mg in plant dry matter and N status of cereals with the nitrogen nutrition index (NNI) and Soil Plant Analysis Development (SPAD) tests. The soil was depleted for a 7-year period from analyzed macronutrients that led to a decrease of available forms of P, K, and Mg, but only a slight crop reduction. Only maize and rape crops, with high nutritional requirements, responded with a decreased yield pursuant to the lack of long-term fertilization with P, K, and Mg. There was a close correlation between K₂O exhaustion and N rates. Soil indices have been more sensitive than plant indices.

Keywords:

• Phosphorus
• plant tests
• potassium
• magnesium
• soil fertility
• soil tests