We study the incorporation processes of indium into group-III nitride layers under pulsed and continuous growth conditions by in-situ reflection measurements. We want to clarify which processes limit the incorporation of indium and lead to a degrading layer structure. The data are discussed in the context of the adlayer model proposed by theory [1], which is a liquid-like layer of group-III atoms on the surface. The adlayer is built-up by the incoming flux but the high vapor pressure of indium leads to a high desorption rate and therefore it is apparent in the data only for low growth temperatures. The data suggests that segregated indium on the surface and the environment also contribute to the indium incorporation process likely also via the adlayer.