Die Bodenkultur - Journal for Land Management, Food and Environment
L. Gruber, R. Steinwender, T. Guggenberger and G. Plakolm:
Comparison of organic and conventional farming on a grassland farm
3rd Communication: Nutrient balances on supply/withdrawal basis and import/export basis
In a grassland farm at BAL Gumpenstein, organic (BE) and conventional farming (KE) were compared in an interdisciplinary experiment lasting 11 years. The experimental groups differed in the treatment of slurry (aeration and addition of rock-meal in BE), the level of fertilization (146 kg/ha mineral N in KE in addition to slurry), in the method of weed control (only mechanical in BE) and the origin of the concentrate for the dairy cows (from organic farms in BE). In group BE and KE, 5.51 and 4.36 ha were used, respectively. Seven cows were kept in each group, which results in a stocking rate of 1.27 and 1.60 cows per ha.
In both treatment groups, nutrient balances were calculated on the basis of supply/withdrawal and import/expert (farmgate). The input and output components for the balances originated mainly from the experimental dara of the production trial. Since the cows were kept on pasture during the summer, some dara (feed intake, excretion of slurry) had to be estimated through regression equations from similar data of this station. The output of nutrients consists of the withdrawal by the plants (supply/withdrawal balance) and of the sale of milk (farmgate balance). The nutrient input results from mineral fertilizer and manure (supply/withdrawal balance) and from mineral fertilizer and purchased concentrates, respectively (farmgate balance). Regarding nitrogen, the mobilisation (60 kg/ha) and symbiontic N fixation (3 kg per % legumes) were additionally taken into account as input in the supply/withdrawal balance.
In case of nitrogen, the supply/withdrawal balance (-1 kg) and farmgate balance (4 kg) per ha agricultural area were more or less balanced in group BE. On the other hand, the N input of 146 kg by mineral fertilizer resulted in a marked surplus of the supply/withdrawal balance (116 kg) and farmgate balance (142 kg) per ha in group KE. The amount of N, additionally supplied by mineral fertilizer and manure (due to higher stocking rate) in group KE was utilized only with an efficiency of 39 % (11 kg DM/kg N)" Regardingphosphorus, input and output were well balanced (supply/withdrawal balance -2 and -3 kg in BE and KE, farmgate balance 3 and 2 kg in BE and KE, respectively). Negative balances were partly found for potassium, which was reflected in decreasing K concentrations in the soil during the experimental years (supply/withdrawal balance -13 und -34 kg in BE and KE, farmgate balance 3 and -10 kg in BE and KE, respectively).
Due to numerous literature data and the present experimental results it has been concluded that the nutrient import with mineral fertilizers is primarily responsible for nutrient surplusses in agriculture, followed by purchased concentrates. If forages as well as concentrates are exclusively produced on the farm and purchased fertilizers are abandoned, a surplus in the nutrient balances cannot arise in livestock farms, since animals will not excrete more nutrients than they have consumed with feedstuffs before. Therefore, feeding livestock animals mainly with nutrients produced on one's own farm to a high extent is the key for well balanced input/output relations (production limited to one's own area). This principle of nutrient cycles is the bearing of biological farming.
Key words: Organic farming, grassland, nutrient balance, supply/withdrawal balance, farmgate balance.