Catch crop nutrient uptake 1st crop rotation cycle

A central aspect when including catch crops into a crop rotation is the conservation of nutrients in their biomass for the subsequently grown crop. Therefore, it is important to qualify and to quantify the nutrient accumulation in the biomass of catch crop species. Since it was often described, that mixtures yield higher biomasses than pure stands of catch crops, we evaluated the nutrient scavenging potential of pure stands vs. mixtures.
Test objects were the four species mustard, phacelia, bristle oat and Egyptian clover either grown in pure stands (sowing densities: mustard - 300, phacelia - 706, bristle oat - 588, Egyptian clover - 833) or in a 4-species mixture (sowing densities: mustard - 67, phacelia - 294, bristle oat - 53, Egyptian clover - 233). Additionally, a commercial mixture of the DSV with a higher species diversity called TerraLife MaisPro was included in the experiment. Their single-species nutrient accumulation was evaluated after 2.5 months of cultivation in total shoot material (dryed for 3 d at 80 °C and ground in a mill) obtained from two sites in Germany (Asendorf - Lower Saxony and Triesdorf - Bavaria), and at two initial starting points of the respective wheat-catch crop-maize long-term rotation (2015 and 2016) - in total 4 test environments.
Generally, nutrient concentrations in the shoot biomass often followed species-specific patterns, e.g. phacelia and oat which are described to have a shallow root system with a high amount of fine roots in the upper soil layers had consistently highest P and K concentrations, S, which is prone to leaching, was most concentrated in the cruciferous species mustard, Ca concentration was highest in phacelia but very low abundant in oat as grass species or Mg was highest in clover since photosynthesis rate must be kept high because biologically fixed N has to be incorporated into carbon skeletons. Increasing interspecific competition in the mix (at higher plant survival rates or at vigorous plant development) favored higher concentrations of several nutrients in some of the species, e.g. higher P concentration in phacelia when cultivated in the 4-species mix. Non-favorable conditions like less water availability led, against this, to higher N concentrations in clover likely due to the establishment of N fixation (Triesdorf 2015 and Asendorf 2016).
However, total nutrient scavenging was largely influenced by the biomass formed by a catch crop variant. In this case, above-ground nutrient conservation capacities were mostly equally high in mustard, phacelia, partially oat and the mixed cultures. Only in one test environment (Triesdorf 2016) where quite loose pure stands established, the mixed cultivation offered a larger nutrient conservation capacity via the production of higher total biomass.