Effects of alternative tillage systems on soil quality and yield of spring cereals on silty clay loam and sandy loam soils in the cool, wet climate of central Norway

Tillage trials were established on a poorly drained silty loam overlying silty clay loam and on a freely drained sandy loam overlying medium sand, in 1988 and 1989, respectively. Autumn and spring ploughing and two ploughless systems were compared for 12-13 years, with three replications at each site. The ploughless treatments comprised deep versus shallow spring harrowing until 1999, and thereafter autumn plus spring harrowing versus spring harrowing only. In 6 years, treatments with and without fungal spraying of the cereal crops were included. In other years, fungicides were not used. Perennial weeds were controlled by herbicides as necessary, on nine occasions up until 2001. Average spring barley (Hordeum vulgare L.) and spring oat (Avena sativa L.) yields were similar with spring ploughing as with autumn ploughing at both sites. In treatments without ploughing, average yields on the silty loam over clay were 93% of those obtained with ploughing, and on the sandy loam over sand they were 81%. Smaller and non-significant yield differences were found between spring harrowing versus deep spring harrowing, and between autumn plus spring harrowing versus spring harrowing only. Fungal spraying increased yields markedly at both sites (25%), but there was no significant interaction between this treatment and tillage system. Oat was compared with barley in 2 years, with oat performing better under ploughless tillage. At both sites increases in penetrometer resistance occurred in the topsoil of unploughed treatments. These were considered particularly limiting on the sandy loam. On the silty loam there was an increase in surface horizon porosity in the absence of ploughing, which was associated with an increase in topsoil organic matter content. On this soil there was also a tendency toward lower penetrometer resistance at >30 cm depth on autumn plus spring harrowed soil than on ploughed soil, indicating that the plough pan may have diminished. This was supported by observations of greater earthworm activity on unploughed soil. Soil chemical analyses revealed that mineral N and plant-available P and K accumulated in the upper horizon under ploughless tillage. The percentage yields obtained in individual years with autumn as opposed to spring ploughing, were positively correlated with air temperature during 0-4 weeks after planting on the silty loam, and with precipitation during 0-12 weeks after planting on the sandy loam. In the case of yields obtained with spring harrowing only, relative to spring ploughing, positive correlations were found with 0-4 week temperature on both soil types, suggesting that low early season temperatures may limit yields under ploughless tillage.