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<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008The measurements of the nitrogen contents accumulated in the biomass of individual cropssuggest that in 2001 the highest nitrogen content was in the red clover underground and overgroundbiomass, which was 4.1 and 2.7 time higher compared with oil radish. The N 2 fixation rate of redclover was 128 kg ha -1 . Of the non-legume crops, the highest nitrogen content was found incocksfoot roots and residues. The highest nitrogen content in the overground mass were found inthe non-legume crop white mustard, 33.1 % higher compared with oil radish. The ability of catchcrops to absorb nitrogen from the soil profile is affected by the rate and depth of the colonization ofthe soil by roots (Kavdir and Smucker, 2005).The data from the second experiment (2003) indicates that the nitrogen content in plantunderground mass was 28.9 % higher compared with those of the first experiment. However, thecontent of the nitrogen in the catch crops overground mass was 36.4 % higher (compared with thatof the first experiment) and the higher contents of nitrogen were accumulated by red clover Thelowest nitrogen content in the plant overground mass was identified in the overground mass ofItalian ryegrasses. According to the averaged data, the ranking among the different catch cropsaccording to nitrogen content in the biomass was: red clover > white mustard > oil radish =cocksfoot > Italian ryegrass.The processes of soil-incorporated organic matter transformation are determined by thecarbon to nitrogen ratio, which is narrower in the plant overground mass compared with theunderground mass (Maiksteniene and Arlauskiene, 2004) In the first experiment (2001) havingincorporated the plant biomass at a more advanced growth stage: of oil radish, white mustard andred clover at the flowering stage, of cocksfoot and Italian ryegrass at the heading stage, the carbonto nitrogen ratio in their biomass was close to the formation of soil humic compounds (Table 3).Table 3. Characteristics of the overground biomass of catch crops (Jonišk÷lis, 2001, 2003)C:N Crude fibre, g kg -1Catch cropExperimentI, 2001 II, 2003 average I, 2001 II, 2003 averageOil radish 18.2 7.9 13.1 215 225 220White mustard 21.6 8.5 15.1 354 203 279Red clover 17.0 11.8 14.4 236 222 229Cocksfoot 24.8 17.7 21.3 306 233 270Italian ryegrass 25.7 19.3 22.5 323 265 294Average 21.5 13.0 17.3 287 229 258LSD 05 3.04 50.5High nitrogen concentration determined that this ratio was the narrowest for oil radish andred clover, whereas in the second experiment (2003) the high concentration of nitrogen in theyoung biomass of Brassicaceae and Leguminosae caused a narrow C to N ratio, in to soilincorporatedorganic matter mineralization. Averaged data suggest that a significantly highercarbon to nitrogen ratio was in the overground mass of undersown grasses compared with that of apostcrop of oil radish.The degree and intensity of soil-incorporated organic matter decomposition is related to itschemical composition: the content of readily decomposable components and lignin in the biomass(Magid et al., 2004). When the biomass of more mature plants was incorporated into the soil,(2001), the content of fibre in it was 25.3 % higher compared with younger plants (2003).Significantly more fibre was accumulated by undersown grasses in the overground part. Theaveraged data of the experiments indicate that with increasing root and overground plant mass theC to N ratio widened (r=0.66, r=0.68; P≤0.05, respectively) and the fibre content increased (r=0.59, r= 0.69; P≤0.05).When barley was grown under the effect of catch crops and their biomass incorporation,the soil nitrogen status varied insignificantly. In the first experiment having incorporated thebiomass of catch crops, the soil total nitrogen did not increase, whereas in the soil with a higher80
<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008total nitrogen status (the second experiment) having incorporated plant biomass with a narrow C:N,an inappreciable nitrogen reduction trend was determined (Table 4).Table 4. The effect of catch crops on the contents of total nitrogen and organic carbon and theirratio in the soil (Jonišk÷lis, 2002, 2004)Total N, g kg -1 Organic C, g kg -1 C:NExperimentCatch cropII,I, 2002 II, 2004 average I, 2002average I, 2002 II, 2004 average2004Without catch crop 1.49 1.64 1.56 12.6 14.3 13.4 8.5 8.7 8.6Oil radish 1.49 1.61 1.55 13.2 14.4 13.8 8.9 8.9 9.0White mustard 1.50 1.61 1.55 13.3 14.3 13.8 8.9 8.9 8.9Red clover 1.50 1.62 1.56 13.1 14.5 13.8 8.7 9.0 8.9Cocksfoot 1.48 1.62 1.55 13.1 14.5 13.7 8.9 9.0 8.9Italian ryegrass 1.53 1.61 1.57 1.33 1.43 1.38 8.7 8.9 8.8Average 1.50 1.62 1.56 1.31 1.44 1.37 8.7 8.9 8.8LSD 05 0.84 0.69 0.54 0.27 0.36This is also corroborated by the statistical analysis of this experiment, which suggests thatwith increasing nitrogen status in the incorporated plant biomass, the total soil nitrogen tended todecline (r= -0.826; P≤0.01). Organic carbon content has a marked effect on heavy textured soilphysical properties, especially its structure and water stability. A more pronounced positive effectof catch crops on the variation of organic C was identified in the first experiment, where a plantbiomass with a more favourable C: N ratio was incorporated. The amount of organic C in the soilincreased after all catch crops, and after white mustard and Italian ryegrass the increase in Ccontent in the soil was significant (5.6 %), compared with the soil without catch crops. The datafrom the second experiment suggest that soil organic carbon varied inappreciably. Averaged dataover the two experiments indicate that catch crops significantly increased soil organic carboncontent (2.2-3.0%), however, the ratio of C to N increased only minutely.Spring barley grain yield depended on the amount of nutrients applied with catch cropresidues and organic manure in the soil (Fig. 1).765432104,245,65Without catchcrop4,025,824,535,714,716,034,145,61 5,474,36Oil radish White mustard Red clover Cocksfoot Italian ryegrassI experimentII experimentFigure 1. Effect of catch crop biomass as green manure on spring barley grain yield (Jonišk÷lis,2002, 2004, t ha -1 )Cereals produced the highest grain yield (5.37 t ha -1 ) in all experiment after red clover; asignificant grain yield increase made up 0.42 t ha -1 , or 8.5 % more than after treatment withoutcatch crop. Overground mass of oil radish and white mustard ploughed in as green manure tendedto increase the spring barley yield 1.6 % and 3.4 % respectively.81
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