Nyttan av stenmjöl, benmjöl och kompost som fosfor- och kaliumgödsel i ekologiskt lantbruk har undersökts i två fältförsök

Seuri, P.

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Organic Eprints

21FORSKNINGSNYTT • Nr 2 • 2002duction balances than crop farms. Iwould be pleased to hear about farms(systems) with high primary nutrientbalances (N > 1,0). Please report if found!Numeric example to count new balances:crop farmP = 100, Y = 80, M = 0=> S = 80/(100+0) = 0,8 (S = Y/(P+M)N = 80/100 = 0,8 (N = Y/P )N = 0,8 * 1,0 = 0,8 (N = S * e,e = (P+M)/P)cattle farmP = 100, Y = 140, M = 120=> S = 140/(100+120) = 0,63(S=Y (P+M)N = 140/100 = 1,4 (N = Y/P )N = 0,63 * 2,2 = 1,4 (N = S * e,e = (P+M)/P => e = (100+120)/100 = 2,2)It is obvious that surface balance (0,63vs 0,8) and farm gate balance (approx.0,2 vs 0,8) is worse on cattle farm thanon crop farm, despite of higher crop pro-duction with same amount of externalnutrients on cattle farm. New methodsindicates the higher production (N = 1,4vs 0,8) due to high circulation rate (e =2,2). Without circulation the potentialmaximum yield is 100, on the cattle farm140 is not the upper limit, yet.Pentti SeuriE-mail: pentti.seuri@mtt.fiTel: +358 15 321 2362M.Sc.Agr Pentti Seuri is researcher at MTTAgrifood Research Finland, EcologicalProduction, Partala.Farmgate balances, cattlebalances, surface balances – howcome we still need one more?Contemporary nutrient balances are verysensitive for production type (crop vs.animal). That is why it is very difficultto compare different types of farms (Myr-beck 1999). A new balance, calledprimary production balance (N), is in-dependent of production type. Primaryproduction balance is formed of twocomponents: surface balance (S) ismultiplied by a circulation factor (e).Thus, we can write: N = S * eWhat is surface balance?Surface balance is widely used in littera-ture and most often it is defined: nu-trients in harvested crop/total nutrientinput. On the crop farm the only nutrientinputs are purchased fertilizers andpossible biological nitrogen fixation.These inputs are called primary nutrients(P), i.e. they come into the farm fromoutside of the farm. On the cattle farm,besides primary nutrients, there aresecondary nutrients, (M) manure, whichmeans that nutrients are recycled on thefarm. With help of these two componentsof nutrients we can define surfacebalance: S = Y/(P + M), where Y isharvested yield.…but never heard aboutcirculation factor before!Right, circulation factor is somethingnew, which is part of this new method!Circulation factor indicates how muchrecycled nutrients (=secondary nu-trients) are utilized in primary produc-tion (= crop production) in proportionA new method to understand nutrient balancesSimple tools to understand information about nutrient balance calculations areintroduced. The primary production balance shows how much crop production isproduced per kilogram purchased nutrients – it doesn’t matter if your farm is acrop farm or a cattle farm, results are comparable between any farms.LitteraturMyrbeck, Å. 1999. Växtnäringsflöden och-balanser på gårdar med olikadriftsinriktningar – En studie av 1300svenska gårdar. Meddelanden frånjordbearbetningsavdelningen, nr 30.SLU.to primary nutrients, thus: e = (P + M)/P. We can note that the circulation factoris 1 if there is no manure on the farm (M= 0). This means that on the crop farmcirculation factor is always 1. On theother hand circulation factor is alwayshigher than 1 if any manure is producedand used on the farm. Note: if manure isproduced outside the farm it is a primarynutrient like any other purchasednutrient.Finally, what do we have?■ We have primary production balance:N = S * e■ On the other hand we have surfacebalance : S = Y/(P+M)■ …and circulation factor:e = (P+M)/P■ If we put them all together we got: N = Y/(P+M)  * (P+M)/P => N = Y/PIf we are only interested in nutrient uti-lization, we can calculate how much nu-trients in yield we can harvest per kilo-gram purchased nutrient (N = Y/P). Butif we are interested to know the compo-nents, like surface balance and circula-tion factor, we use the equation N =S*e. Theoretically a surface balance can'tbe higher than 1 (without changes insoil N). In practice the crop farm canreach values as high as 0,7 – 0,80 (Myr-beck 1999), but cattle farms get mosttypically values below 0,5. However,since there is no circulation at all on thecrop farm, total utilization rate is 0,7 -0,8 (i.e. to harvest a yield of 0,7 kg nitro-gen 1,0 kg nitrogen is needed fromoutside the system). Potentially, cattlefarms can reach higher primary pro-■

A new method to understand nutrient balances

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