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 farmi ng (KE) were compared in an interdisciplinary experiment lasting 11 years. The experimental groups differed in the treatment of slurry (aeration and a ddition 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 mechan ical in BE) and the origin of the concentrate for the dairy cows (from orga nic farms in BE). In group BE and KE, 5.51 and 4.36 ha were used, respectiv ely. Seven cows were kept in each group, which results in a stocking rare o f 1.27 and 1.60 cows per ha. In both treatment groups, nutrient balances were calculated on the basis of supply/withdrawal and import/export (farmgate). The input and output compo nents for the balances originated mainly from the experimental data of the production trial. Since the cows were kept on pasture during the summer, so me data (feed intake, excretion of slurry) had to be estimated through regr ession equations from similar data of this station. The output of nutrients consists of the withdrawal by the plants (supply/withdrawal balance) and o f the sale of milk (farmgate balance). The nutrient input results from mine ral fertilizer and manure (supply/withdrawal balance) and from mineral fert ilizer and purchased concentrates, respectively (farmgate balance). Regardi ng nitrogen, the mobilisation (60 kg/ha) and symbiontic N fixation (3 kg pe r % legumes) were additionally taken into account as input in the supply/wi thdrawal balance. In case of nitrogen, the supply/withdrawal balance (-1 kg) and farmgate bal ance (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 i n a marked surplus of the supply/withdrawal balance (116 kg) and farmgate b alance (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). Regarding pho sphorus, 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, respectiv ely). Negative balances were partly found for potassium, which was reflecte d 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 primar ily responsible for nutrient surplusses in agriculture, followed by purchas ed concentrates. If forages as well as concentrates are exclusively produce d on the farm and purchased fertilizers are abandoned, a surplus in the nut rient balances cannot arise in livestock farms, since animals will not excr ete more nutrients than they have consumed with feedstuffs before. Therefor e, feeding livestock animals mainly with nutrients produced on one's own fa rm to a high extent is the key for well balanced input/output relations (pr oduction limited to one's own area). This principle of nutrient cycles is t he beating of biological farming.