Energy balances and SOC and N stocks as affected by organic amendments and inorganic N fertilization in a semi-arid environment (IOSDV-Madrid)

Abstract

A long-term field experiment (1984–2011), was conducted on a Calcic Haploxeralf from semi-arid central Spain to evaluate the combined effect of three treatments: farmyard manure (FYM), straw and control without organic amendments (WOA) and five increasing rates of mineral N on: (1) some energetic parameters of crop production, and (2) the effect of the different treatments on soil organic carbon (SOC) and total N stocks. Crop rotation included spring barley, wheat and sorghum. The energy balance variables considered were net energy produced (energy output minus energy input), the energy output/input ratio and energy productivity (crop yield per unit energy input). Results showed small differences between treatments. Total energy inputs varied from 9.86 GJ ha−1 year−1 (WOA) to 11.14 GJ ha−1 year−1 in the FYM system. For the three crops, total energy inputs increased with increasing rates of mineral N. Energy output was slightly lower in the WOA (33.40 GJ ha−1 year−1) than in the two organic systems (37.34 and 34.96 GJ ha−1 year−1 for FYM and straw respectively). Net energy followed a similar trend. At the end of the 27-year period, the stocks of SOC and total N had increased noticeably in the soil profile (0–30 cm) as a result of application of the two organic amendments. Most important SOC changes occurred in the FYM plots, with mean increases in the 0–10 cm depth, amounting an average of 9.9 Mg C ha−1 (667 kg C ha−1 year−1). Increases in N stocks in the top layer were similar under FYM and straw and ranged from 0.94 to 1.55 Mg N ha−1. By contrast, simultaneous addition of increasing rates of mineral N showed no significant effect on SOC and total N storage.