Evaluation of different harvesting methods in field experiments with cereals and consequence for the calculation of fertilizer N uptake

Exact determination of N uptake by crops is necessary for comet estimations of recovery of fertilizer N in field trials, especially if the fate of app lied N is under consideration. In 1995 (2 sites winter barley, 1 site winte r wheat) and 1996 (3 sites winter wheat) it was examined in field trials wh ether the results for total dry matter, N uptake and N fertilizer uptake di ffer between mechanically (plot harvester; PH) and manually (cut by hand; C H) harvested cereals on the same site. The effect of harvesting methods on the parameters was analyzed in different N treatments. In each field trial total dry matter and N uptake thereof were higher for t he treatment CH in comparison to PH. Both parameters differed most substant ial between harvesting methods in 1995 when straw was collected from the gr ound after harvest. In particular dry matter and N uptake in straw and resi dues were significantly lower for PH. At highest N supply treatments (265 k g N/ha) the difference was 11-52 kg N/ha. In 1996 a box was mounted at the harvester to collect straw directly. However, N uptake was found to be up t o 35 kg N/ha lower for treatment PH. Highest differences between harvesting methods occurred generally when crops were layered which is often the case in N trials with high N rates. Fertilizer N uptake (= N uptake in fertiliz ed minus N uptake unfertilized plots) was up to 56 kg N/ha higher in 1995 a nd up to 23 kg N/ha higher in 1996 for CH compared to PH. Recovery of ferti lizer N (= fertilizer N uptake x 100/N application) was 4-22 % (1995) and 4 -14 % (1996) higher for CH. From the results of this investigation it is concluded that for studies wit h a main focus on N fertilizer recovery han est of cereals should be done m anually in particular when lodging of crops occurs. However even without lo dgings there is a high preference for manual harvesting if complete dry mat ter determination of straw and residues is important for the conclusions.