Season-long supply of plant-available nutrients from compost and fertiliser in a long term organic vs. conventional snap bean rotations experiment

Summary

In Canada, stockless organic vegetable cropping systems may use compost for fertility. However, information to guide growers about when nutrients become available in the soil over the growing season is lacking. Detailed analysis of plant nutrient supply was conducted over three years in a multi-site rotations experiment using two cropping sequences. The experiment compared conventional fertility treatment (synthetic fertiliser (1x N)) with organic treatments (annual compost amendment at a low (1x N) and a high rate (3x N)). Plant-available soil nutrients were captured using sequential two-week burials of ion exchange membranes. Ions were eluted and quantified. Variation in nutrient supply over time, and effects attributable to crop rotation and fertility regime were evaluated with analysis of variance and of principal components. Results showed season-long supply of plant nutrients was more affected by year than fertility regime or rotation, even in composted plots where large residual effects were expected. Synthetic fertiliser and 1x compost resulted in very similar seasonal plant nutrient supplies. While 3x compost caused some significant changes, the gains in plant nutrient supply was modest enough to suggest little or no advantage in this one respect to warrant the cost of amending at greater than the 1x rate.