Soil fertility and crop productivity: medium-term effect of organic inputs and simplified cultivation techniques

The combined effects of the nature of fertilizers (NPK, manure + NPK and liquid manure + NPK), fractionation of the manure inputs (every year or every three years) and tillage (plowing and reduced-tillage) associated with two nitrogen rates (100 or 60 % of the optimal dose) on soil fertility and dry matter production of different crops have been studied from 1997 to 2009 in Changins. After twelve years of trial, different soil analyses show that nitrogen fertilization had no effect on soil fertility, only the soil organic matter and total nitrogen contents differed significantly between treatments. In terms of non-limiting nitrogen fertilization, crops treated with manure produced significantly more dry matter than those treated with only inorganic fertilizer. A sub-fertilization with only 60 % of the nitrogen fertilizer needs causes a decrease in production of 7-13 % according to the treatments. In the absence of the manure input, reducing tillage keeps the stock of soil organic matter, but should be accompanied by a strengthening of nitrogen fertilization. Split manure in annually low inputs doesn’t increase the manure efficiency.