Interactions between soil organic matter level and soil tillage in a growing crop: N mineralization and yield response

Summary

Effects of organic matter management and soil loosening on the synchrony between soil N mineralization and crop N demand were studied in a field experiment. Four different levels of organic matter (OM) were applied to a crop rotation during 12 years by various applications of animal manure, straw incorporation and catch crop growing. A spring barley crop was grown to test the influence of the previous OM applications. Soil loosening with a row cultivator was carried out one, two or three times in the first part of the growth season to examine the potential for adjusting soil N mineralization by soil tillage in cropping systems with different OM input. Immediately before each of the soil loosenings and again after one, two and three weeks, plant biomass and soil were sampled from subplots.
Soil receiving only mineral fertilizer without extra input of organic matter generally contained less nitrate than soil with annual supply of animal slurry, straw and catch crop material. Soil loosening raised the nitrate content compared with undisturbed soil. The maximum increase in soil nitrate after soil loosening was estimated to 27 kg NO3-N ha-1 14 days after soil loosening. The soil loosening only had a minor influence on N and dry matter (DM) in the barley harvested at the same time as the soil sampling.
The temporal pattern of both DM production and N uptake were more influenced by OM levels than by soil loosening. Barley grown on soil without extra OM input and with all N supplied with mineral fertilizer developed faster in the first part of the growth season than barley receiving part of its N input with slurry. However, the N uptake in dry matter was less affected causing higher N concentrations in DM on soil with extra annual OM inputs. At maturity, both grain DM yield and N uptake were highest at soil with the highest OM input. The soil loosening did not significantly influence barley dry matter yield but the total N uptake was slightly higher (5 kg N ha-1) with only one soil loosening. It appears that application of OM as slurry, straw and catch crop had a pronounced influence on crop development and N availability but soil loosening did not significantly improve the synchrony between soil N mineralization and crop N demand.