Suitability of Carbon and Nitrogen Management Indices for the Evaluation of Soil Organic Matter under Different Soil Management Practices in a Productive Vineyard

Soil organic matter (SOM) is considered to be the most important part in the soil. C and N and their forms are most often used to evaluate SOM. In the last decades, C indices have begun to be used to assess soil quality for C changes in SOM due to the different soil management. Since C cycle is closely related to N, there is an assumption that N indices (derived in the same way as C indices) will be sensitive to N changes in SOM under the different soil management. The objective of the study was to evaluate the extent of C and N indices on C and N changes in SOM (in Rendzic Leptosol) under the different soil management practices (1. G: grass and no fertilization – as control; 2. T: tillage; 3. T+FYM: tillage + farmyard manure; 4. G+NPK3: grass + NPK 125–50–185 kg ha-1; 5. G+NPK1: grass + NPK 100–30–120 kg ha-1) in a productive vineyard (Nitra-Dražovce; Slovakia) during the period of 13 years. The results showed that the soil organic carbon (SOC) was reduced by 26% compared to G because of intensive cultivation on one hand, but on the other hand, in T + FYM treatment no significant changes in SOC over the 13 years of the experiment were observed. A higher labile carbon (CL) content was in G+NPK3 then follows: G+NPK1 > G > T+FYM > T for topsoil (0-30 cm). In topsoil, carbon lability increased after a higher level of mineral fertilization, while in subsoil (30-60 cm) after intensive cultivation. The values of CPI for topsoil decreased in the following order: G+NPK1 > T+FYM > G+NPK3 > T. Based on CMI values, intensive C changes in the SOM due to the soil management practices were observed in T treatment. The highest accumulation of carbon and decomposable organic matter occurred in G+NPK3. Incorporation of FYM, and both rates of NPK increased values of NMI by 45, 47 and 36% respectively compared to intensive tilled treatment for topsoil. The highest values of the NPI were detected because of farmyard manure application and mineral fertilization at a higher rate (NPK3) for topsoil and because of intensive cultivation between vine rows as well as plowing of FYM for subsoil.