Use of a partial-width tillage system maintains benefits of no-tillage in increasing total soil nitrogen

Tillage treatments had impact on total soil nitrogen (N) storage and consequently on soil carbon (C) sequestration. The objective of this study was to assess effects of long-term (1992–2010) tillage practices, including a partial-width tillage system (paraplow) on N concentration and stratification. The tillage treatments were: no-tillage (NT), minimum tillage (18–22 cm depth) with chisel plow (MT), conventional tillage (25–30 cm depth) with mouldboard plow (CT) and zone-tillage subsoiling (25–30 cm) with a paraplow (ZT) applied in alternate years in rotation with NT. The soil was a Calcic Haploxeralf from Central Spain. The crop rotation was chick pea (Cicer arietinun L.) cv. Inmaculada/barley (Hordeum vulgare L.) cv. Volley. The equivalent mass approach was used to compare N stocks in the various tillage methods. Tillage treatments had significant effects on soil bulk density and no-till increased soil bulk density of the top layer. At the end of 19 years, the stocks of N had increased under NT compared with MT and CT. Most changes occurred within the 0–5 cm layer, where plots under NT had 0.48 Mg N ha−1 and 0.53 Mg N ha−1 greater than in MT and CT, respectively. Zone tillage maintained most of the long-term benefit of NT in increasing N stocks in the top layer (0–5 cm). At the end of the experiment, total N concentration in the 0–5 cm depth under ZT was 42% and 53% higher that under MT and CT, respectively. Stratification ratios of N from 1992 to 2000 showed no significant differences between NT, MT and CT. In contrast, from 2001 onwards, all stratification ratios were significantly higher in NT than in the other two tillage systems. In addition, in 2010 the stratification ratio of N in NT was >2 and more than 2-fold those obtained in MT and CT. Values of stratification ratios under ZT followed the same trend than under NT and were significantly greater than under MT or CT. These greater stratification ratios of N observed under NT and ZT confirm, in the soil studied, not only the benefits associated with the long-term application of no-till in increasing total N in the top layer, but also the positive impact of the use of a paraplow as a rotational tillage system.

► Long-term changes in tillage methods affect soil bulk density.
► Stocks of N increased under no-till compared with minimum and conventional tillage.
► No-till increased the stratification ratios of N.
► Paraplow applied in alternate years maintains the benefits of no-till in increasing stocks of N and N stratification ratios.