Effect of tillage, lime sludge and cover crop on soil physical state and growth of spring oilseed rape

Research was carried out during 2008-2010 at the Joniškėlis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry on a clay loam Endocalcary-Endohypogleyic Cambisol (CMg-n-w-can).The aim of the present study was to determine effects of deep (20-23 cm) and shallow (15-17 cm) ploughing, ploughless tillage (10-12 cm), combinations of ploughless tillage (10-12 cm) with incorporation of lime sludge and cover crop (mixture of field pea, common vetch and blue lupine) for green manure and application of the same cover crop for mulch without autumn tillage on soil physical properties and growth of spring oilseed rape (Brasica napus L.) crop.After shallow ploughing the soil water content in seedbed (0-5 cm) for spring oilseed rape right after its sowing was significantly lower in droughty years (with duration of post-sowing period without rainfall for 18 and 20 days in 2008 and 2009, respectively) and crop emergence was worse compared to deep ploughing.Due to ploughless tillage, the soil water content in seedbed was significantly lower in droughty years and seedbed structure was worse in sufficiently wet year compared to deep ploughing.Incorporation of lime sludge by ploughless tillage resulted in significantly higher soil water content at 5-15 cm depth, better seedbed structure and greater crop germination rate compared to ploughless tillage alone.Incorporation of lime sludge also increased oilseed rape yield by 11.1% in droughty year.Having incorporated the cover crop for green manure late in autumn by ploughless tillage the oilseed rape in droughty years germinated significantly worse, the soil water content remaining in the seedbed after emergence was lower and the yield decreased by 19.8% compared to ploughless tillage.Having left the cover crop mulch over winter without autumn tillage demonstrated significantly higher soil water content at 5-15 cm depth after oilseed rape sowing; however, in droughty years the seedbed became drier, its structure deteriorated, the crop germinated worse and yield decreased by 12.1-17.3%compared to ploughless tillage.Spring oilseed rape germination rate in droughty years was influenced by the soil water content in the seedbed after sowing (r = 0.56, P < 0.01), content of 2-5 mm soil aggregate fraction in seedbed (r = 0.50, P < 0.05) and by the seedbed structure, expressed as an index (r = 0.50, P < 0.05), while crop yield -by the seedbed structure (r = 0.67, P < 0.01) and by the germination rate (r = 0.74, P < 0.01).