Effects of organic amendments on soil carbon content and microbial biomass – results of the long-term box plot experiment in Grossbeeren

Abstract

The Box Plot Experiment in Grossbeeren was set up in 1972 to investigate diverse fertilization strategies within an irrigated vegetable crop rotation system for three different soils. Here we report on the long-term effects of applying different organic amendments and mineral N fertilizer levels to soils on the content of: (1) microbially decomposable carbon (Cdec); and (2) microbial biomass carbon (Cmic). We determined the Cdec content of soils that were covered with a vegetable crop rotation, and established that the differences between treatments with and without organic amendments corresponded very well to those found under arable crop rotations. Under the given experimental conditions, leaving the crop residues on the field generated an optimum level of soil organic matter content. When we compared the Cdec content of the soils after applying different organic amendments as based on the C input, we found them to be similar. 10 t ha − 1 yr − 1 farmyard manure (FYM) has been reported to be sufficient to generate an optimum level of organic matter in arable soils. Here we show that this effect can also be transferable to other organic amendments if the C input is used as the reference base. Regarding Cmic content, we obtained a linear relationship for the differences of Cdec between treated plots which were influenced by different C input and the controls. This relationship did not differ with soil type. Therefore, we assumed that Cdec may be regarded as a permanently present substrate for the nutrition of microorganisms regardless of soil type.