Are Selge

Changes in agricultural land use and in plant nutrient balances of arable soils in Estonia

Abstract The aim of the present study was to assess the impact of changes in agricultural land use and in the plant nutrient balances on the degradation of soils in Estonia. The plant nutrient balances of arable soils in Estonia were calculated at the national level. After the re-establishment of the independence of Estonia, in the transition to market economy, agricultural production has undergone a drastic decline. Agricultural land use has declined most of all in the regions with low soil fertility. Decreased and low-input agricultural production has reduced pressure on the surrounding environment but owing to the inadequate use of fertilizers, the balance of the main plant nutrients is at present negative. In the 1990s, crop production has occurred largely at the expense of soil resources. Current agri-environmental policy should be supplemented with measures for preventing degradation of soils due to the depletion of plant nutrient reserves of arable soils.

The effects of pure and undersowing green manures on yields of succeeding spring cereals

Abstract A field experiment was conducted in 2004–2006 to investigate the effect of green manure treatments on the yield of oats and spring barley. In the experiment, different green manure crops with undersowing and pure sowing were compared for amounts of N, C, and organic matter driven into soil and their effect on cereal yield. The spring barley field had a total of 41.7–62.4 kg N ha−1 and 1.75–2.81 Mg C ha−1 added to the soil with straw, weed, and roots, depending on the level of fertilisation; with red clover, and both common and hybrid lucerne undersowing, with barley straw and roots, the values were 3.45–3.96 Mg C ha−1 and 139.9–184.9 kg N ha−1. Pure sowings of these three leguminous green manure crops had total applications of 3.37–4.14 Mg C ha−1 and 219.7–236.8 kg N ha−1. The mixed and pure sowing of birds-foot trefoil provided considerably less nitrogen and carbon to the soil with the biomass than with the other leguminous crops. Application of biomass with a high C/N ratio reduced the yield of the succeeding spring cereals. Of the green manures, the most effective were red clover and both common and hybrid lucerne, either as undersowing or as pure sowing. Undersowings with barley significantly increased the N supply for the succeeding crop without yield loss of the main crop compared with the unfertilised variant. Compared with ploughing-in of green manure in autumn, spring ploughing gave a 0.2–0.57 Mg ha−1 larger grain yield.

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.