Effects of soil tillage and fertilization on resource efficiency and greenhouse gas emissions in a long-term field experiment in Southern Germany

Two factorial long-term field experiments were carried out at the experimental site of Scheyern, located in southern Germany, 40. km north of Munich (48°30'0' N, 11°26'60' E). Here three soil tillage systems were investigated: CT (conventional tillage with moldboard plough, 25. cm plowing depth), RT1 (reduced tillage with chisel plow, 18. cm working depth), and RT2 (reduced tillage with chisel plow, 8. cm working depth). At the same time, three fertilization systems were analyzed (high (N3), medium (N2) and low (N1) mineral N input) with a crop rotation of winter wheat (Triticum aestivum L.) - potatoes (Solanum tuberosum L.) - winter wheat-corn (Zea mays L.). The long-term effects of tillage and fertilization on yields, soil properties, nitrogen and energy efficiency, as well as greenhouse gas emissions (GGE) were investigated for the period of 1994-2005.On average conventional tillage (CT) produced yields of 8.03 (N1), 8.82 (N2) and 8.88 (N3) GE (grain equivalents) ha^-1yr^-1; reduced tillage (RT1) yields of 7.82 (N1), 8.54 (N2) and 9.10 (N3) GE ha^-1yr^-1 and RT2 yields of 6.9 (N1), 7.82 (N2) and 8.6 (N3) GE ha^-1yr^-1.The benefit of reduced soil tillage over CT is a lower consumption of diesel fuel (reduced by 35%) and fossil energy (by 10%), C sequestration and N accumulation in soil. We recorded the highest soil organic carbon (SOC) in the RT2 treatments with the lowest tillage intensity (52.5Mgha^-1) and the lowest SOC reserves in the CT plowed treatments (41.1Mgha^-1). During the reported period, SOC reserves in the plowed treatments decreased by about 300kgCha^-1yr^-1, whereas they increased by 150-500kgCha^-1yr^-1 in the chiseled treatments. Similar results were achieved with the soil organic nitrogen (SON) reserves based on the type of tillage. This amounted to around 4000kgha^-1 (CT), 4500kgha^-1 (RT1) and more than 5000kgNha^-1 (RT2).The RT1 treatments were marked by high nutrient and energy efficiency. The disadvantage of reduced tillage lies in higher pesticide consumption and stronger soil compaction. The influence of reduced tillage was more pronounced in RT2 than in RT1 (higher SOC and SON content, higher soil dry bulk density, lower consumption of diesel fuel, higher pesticide input). The significant decreases in yield in the RT2 treatments reduced the nitrogen and energy efficiency and raised yield-related greenhouse gas emissions (GGE) in comparison to the RT1 treatments. In the case of reduced tillage combined with high N doses (RT1/N3, RT2/N2, RT2/N3), high N₂O emissions of 10 to 12kgha^-1yr^-1 were measured using closed chambers. It was found that as input of mineral N increased, GGE for tillage treatments, both area and yield related also increased. In RT1/N1, negative net GGE were recorded due to high C sequestration combined with moderate N₂O and CO₂ emissions (-220kg CO_{2 eq} ha^-1yr^-1, -28kg CO_{2 eq} GE^-1), whereas CT/N3 produced the highest net GGE (3587kg CO_{2 eq} ha^-1yr^-1, 404kg CO_{2 eq} GE^-1).