Effect of land management without farmyard manure application on the amount and the ectivity of soil microbial biomass

Four kinds of cereal crops were grown without farmyard manure application. The effect of farmyard manure was supposed to be replaced by post-harvest residues (PH treatment) or by ploughing the total by-product, i.e. straw (PZ treatment) into soil. After seven years of application, this soil farming system did not influence the contents of Cox and Nt in soil. The amount of organic carbon had declined after the first year, but in the following years it remained at the same level (1.2%). The total nitrogen content increased from 0.143 to 0.166% without any considerable difference between the treatments. The amount of microbial biomass (Cmic) in PH treatment had been varying and in 2000 it decreased approximately by a half (from 215.96 to 132.00 mg C/kg of soil dry matter). The input of organic matter due to ploughing the whole by-product (PZ treatment) into soil acted favourably and the value of Cmic in 2000 was quite comparable with the average values of the individual years of 1994-1997. This land management and cereal growing caused a reduction of the ratio of microbial biomass carbon to soil organic carbon (Cmic/Corg). In the year 2000, the values decreased from 2.59 to 1.09% and from 2.88 to 1.82% in PH and PZ treatments, respectively. The amount of the biologically releasable nitrogen (Nbiol) and the intensity of nitrification were the highest in the year 2000. There was a moderate negative correlation (r = -0.474) between the Nbiol values and biomass amount values in PZ treatment, and a very close negative one (r = -0.972) in PH treatment. This relation became strong in both treatments when the values Cmic/Corg and Nbiol were compared, i.e. rPH = -0.863 and rPZ = -0.921. The results confirmed that the amount and the quality of organic matter influence microbial biomass and its activity which is responsible for the nutrient release.