Effects of catch crops cultivated for green manure and mineral nitrogen fertilization on soil enzyme activities and chemical properties

Abstract

Use of catch crops as a green manure may increase soil fertility due to improved soil organic matter content as well as soil biological activities. We conducted a 3-year field experiment to evaluate the impact of catch crops [oilseed radish (OR) (Raphanus sativus L.) and field pea (FP) (Pisum sativum L.)] and inorganic N fertilization at 0, 40, 80, 120, 160kgNha−1year−1 on the activities of soil enzymes (β-glucosidase — GLU, nitrate reductase — NR, urease — UR, arginine deaminase — ADA, acid and alkaline phosphatase — PAC and PAL) and chemical properties of typical Alfisol. Each year, catch crops were sown at the beginning of August and ploughed three months later in 2005, 2006 and 2007. Then the main crop – spring wheat (Triticum aestivum L.) – was grown in 2006, 2007 and 2008. Soil samples were taken twice a year, in spring before spring wheat sowing (March or April) and in summer, immediately after the harvest. In March (April 2006) organic carbon (CORG) and available potassium (KAVAIL) did not show significant changes as influenced by catch crops. Total nitrogen (NTOT) content was significantly lower in control soil than in catch crop treatments, while the concentration of available P (PAVAIL) behaved in the opposite way. N fertilization rates did not significantly affect the chemical properties of soil without catch crops (C) (with the exception of MgAVAIL concentration). In contrast, the chemical properties did not show clear tendencies depending on N fertilization in soil with field pea or oilseed radish. Significantly higher soil enzymatic activities were observed in the catch crops treatment than in the control (C). The studied enzymes also showed a significantly higher activity in the FP than in the OR when both catch crops were compared (with the exception of ADA and PAL activities in August and GLU activity in March (April 2006)). Both PAC and PAL as well as GLU, ADA and NR activities were always higher in August than in March (April 2006), while UR (with the exception of 2007) behaved in a reverse manner. The enzyme activities were 10–26% lower at a rate of 160kgNha−1year−1 compared to the highest activity noted in the case of a rate of 40 and/or 80kgNha−1year−1 with the exception of UR activity, which was unaffected by N fertilization rates. Cultivation of catch crops for so-called green manure can be useful management practice for enhancing soil biological activity as evaluated by enzymatic activity. Enzyme activities were more sensitive to the presence of catch crop green biomass and N fertilization rates than chemical properties. Therefore, they might be useful as an early indicator in the evaluation of the alteration of soils caused by different agricultural activities.