The Box Plot Experiment in Grossbeeren after eight rotations: nitrogen,carbon and energy balances

The Box Plot Experiment in Grossbeeren was set up in 1972 to investigate the efficiency of diverse fertilization strategies within an irrigated vegetable crop rotation system for three different soils. Here, we report on the long-term effects on nitrogen, carbon and energy balances of applying various organic amendments and different amounts of mineral N fertilizer to soils. Fertile soils (sandy loam and clayey silt) were characterized by higher yield and N removal potential by plants, higher acceptable N input amounts, and a higher proportion of total N input recovered by soil N storage and N uptake by plants. After 40 years, organic carbon equilibrium in the soil has not been reached. Rates of change of organic carbon stocks are still affected by the different organic matter levels at the beginning of the experiment. An increasing net N supply increased and organic C input decreased net C gains. Because of the manifold possibilities of producing energy from current or former agricultural land, energetic evaluation of land use needs to become more complex if direct comparisons are to be made. Including the energy contents of organic amendments and soil organic matter in the energy balances would be a first step in this direction.