Long-term management impacts on soil C, N and physical fertility

For many centuries manure application to the soil has been common practice. Organic amendments and fertiliser applications can increase crop yields and soil organic matter (SOM). However, the long-term impacts on soil physical fertility are often neglected. This study was carried out on the Broadbalk Wheat Experiment at Rothamsted, UK, established in 1843 on an Aquic/Typic Paleudalf soil. Application of farmyard manure (FYM), N fertiliser and wheat straw on total organic C (CT), labile C (CL) and non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) were studied on wheat (Triticum aestivum) and adjacent woodland and pasture areas. Manure additions, N fertiliser and straw incorporation increased all C fractions, particularly the CL fraction. The addition of 35 t ha−1 year−1 of FYM increased CT to 2.5 times that of the control (no fertiliser) treatment and CL to 5 times that of the control. With highest N application and straw returned, CT increased by 1.3 times and CL by 1.5 times that of the control treatment. There were linear relationships between rate of N fertiliser applied and all C fractions, with the rate of increase almost double with straw than straw removed. Manure application improved MWD, as did high N fertiliser additions with straw returned. Application of N fertiliser only increased MWD and Kunsat (at 10 mm tension) if straw was returned, while the addition of manure resulted in decreased Kunsat. The highest Kunsat rate was on the high N fertiliser, straw returned treatments. The uncropped areas all had high soil structural stability. Similar relationships occurred between all C fractions and NT and MWD for the high C soils, but relationships were much stronger with CL than the other C fractions in the low C soils. These results showed that soils with low C concentration are more reliant on CL for structural stability.