Tiina Köster

Effect of Cut Plant Residue Management and Fertilization on the Dry-Matter Yield of Swards and on Carbon Content of Soil

The goal of this research was to study the impact of cut plant residues, returned to or removed from the grassland sward, on the dry-matter yield of swards and on the organic carbon (Corg) concentration of soil. The experiment was carried out during 2004–2008. The variables of the experiment were (i) sward type: turfgrass sward (Festuca rubra rubra and Poa pratensis) and grass–clover sward (Phleum pratense, Lolium perenne, and Trifolium repens) and (ii) treatment of residues: the cut plant residues were returned (RRT) to the plots or removed (RRM) from the plots after the mowing. The fertilizer treatments were as follows: N0P0K0, N80P11K48, N160P22K96, and N400P56K240 kg ha−1 for the turfgrass sward and N0P0K0 and N80P26K50 kg ha−1 for the grass–clover sward. The Corg and Ntot concentrations in the 20-cm soil layer were measured at the beginning and at the end of the experiment at depths of 0–5 cm and 5–20 cm. Nitrogen was returned as plant residues to the grass–clover sward in treatment N0P0K0 at 190 kg ha−1 and N80P26K50 at 204 kg ha−1 and consequently the returned cut plant residues increased the yield by 31% and 22%, respectively. The amount of N returned as residues to turfgrass sward was 31–236 kg ha−1 but it had no significant influence on the sward dry-matter yield. During the 5 years of the experiment the Corg content in 0- to 5-cm soil layer of grass–clover sward in treatment RRT increased by 42.9% and in RRM by 32.0% as an average of both fertilization treatments. At the depth 5–20 cm the Corg concentration did not change in treatment RRT, but in treatment RRM with fertilization the Corg concentration decreased by 8.2%. In turfgrass soil the Corg concentration increased in RRT treatment by 21.6% and in treatment RRM by 7.2% during 5 years. In the lower soil layer the concentration of Corg decreased with removal and return of plant residues. The fertilization did not influence the changes of Corg concentration in turfgrass swards soil.

The decomposition of turfgrass clippings is fast at high air humidity and moderate temperature

Abstract In grassland areas where herbage production has no economic value, the cut grass is often left on the sward surface where its decomposition is influenced by weather conditions. Although the influence of temperature and humidity on decomposition has been investigated under controlled lab conditions, experimentation has generally been under ideal moisture conditions that have not tested the combinations of climatic limitations that might occur in the field. The decomposition of mown turfgrass clippings deposited at different times of vegetation period was studied in situ using nylon bags during the first 8 weeks after deposition to investigate the effect of weather conditions (the air temperature, relative humidity, precipitation) on decomposition. Decomposition is the highest in the case of high air humidity and temperature of 10°C. Limiting factors for decomposition at temperatures above 10°C is the air humidity and below 10°C the air temperature. The general tendency was that the rate of decomposition increased with increasing air temperature up to 10°C, but with further increases of air temperature the decomposition rate slowed down. Relative air humidity had a variable impact (at the beginning of the decomposition process (weeks 1–2) the influence was negative, during weeks 3–8 of the decomposition process the effect was positive), and hence had no generalized relationship with decomposition over the studied decomposition period (weeks 1–8). The most significant influence of weather conditions on the decomposition rate was recorded directly after cutting. If the cutting was done during hot weather conditions, the material was drying fast and therefore decomposed slowly. Our results indicate that for fast decomposition of clippings it is important to maintain the freshness of material. Lower decomposition rates occurred during conditions of hot and dry weather, and also cooler (temperature near to 0°C) weather, and can be compensated as soon as favourable weather arrives.

Erosion-affected soils in the Estonian landscape: Humus status, patterns and classification

In Estonia, areas threatened by erosion are mainly situated in the south-east, where erosion-affected soils (EAS) account for 6–37% of the total area. The main tasks of this research were: (i) To characterize the humus status of EAS by their subdivisions, (ii) to define the humus status forming peculiarities of EASs, and (iii) to analyse the distribution and association of EASs with uneroded soils. To characterize the humus status of EAS epipedon thickness (cm), humus concentration (g kg−1) and humus pool (Mg ha−1) were used. For the determination of humus status parameters via sampling points, the transect method was used. The humus status of EAS varied widely (average humus concentration varies from 12–45 g kg−1 and humus pools from 39–191 Mg ha−1). The mean humus pools in eroded (n = 174), transitional (n = 224) and deluvial/colluvial (n = 159) soils are accordingly 51 ± 18 (mean ± SD), 90 ± 23 and 138 ± 67 Mg ha−1, respectively. The mean decrease in humus pools of eroded (E) soils on arable lands is 32–53 Mg ha−1, but the mean increase in deluvial (D) soils is 14–76 Mg ha−1. The greatest humus pool relocation coefficients D/E (2.8–3.3) are characteristic of the soils of hilly end moraine areas.