Maize/oats forage rotation under 3 cultivation systems, 1978–83

Abstract

Abstract Soil conditions in the tillage zone (0– 300 mm) of a Tokomaru silt loam were monitored for 3 seasons of a long‐term continuous maize/oats forage cropping trial using different methods of crop establishment — plough/disc/harrow cultivation, minimum cultivation (disc/harrow), and non‐cultivation. Non‐cultivation resulted in higher soil bulk densities, larger structural units (aggregates), and lower porosities — particularly in the larger ‘aeration’ pore sizes (macropores) — compared to more conventional cultivation methods. Infiltration rates were significantly retarded by the non‐cultivation treatment but water retention in the plant‐available range was improved slightly. Ministry of Agriculture and Fisheries Quicktests showed an accumulation of phosphorus (P) and potassium (K) in the uppermost soil layer (0–50 mm) on direct‐drilled plots, whereas the cultivated soil had a more homogeneous fertility status throughout the 0–300 mm zone. The soil physical and fertility conditions for minimum cultivation tended to be intermediate between non‐cultivation and conventional cultivation treatments. Soil aggregate stability, pH, organic carbon, and Quicktest calcium (Ca) and magnesium (Mg) levels were not significantly affected by the method of tillage. Crop establishment and early plant growth were influenced by soil structural conditions in the seed zone. However, the effects of soil conditions resulting from the different tillage treatments on final crop yields were complicated by other factors. The continuous cropping regime used in this trial caused only a slight deterioration of soil structural conditions New Zealand Soil Bureau publication 970. Received 17 September 1984; revision 11 January 1985 compared to an adjacent grazed pasture. Topsoil pH and Mg showed declining trends and there was a significant drop in MAF Quicktest Ca levels in the uppermost 100 mm, with a simultaneous buildup of Ca below this depth. Fertiliser applications maintained or improved the levels of MAF Quicktest K and P. The results of these changes in soil conditions with continuous cropping on crop yields were inconclusive, but may be linked with the declining oat yields. Maize yields appeared to be more related to climatic and other factors.