SOIL β-GLUCOSIDASE ACTIVITY UNDER WINTER WHEAT CULTIVATED IN CROP ROTATION SYSTEMS DEPLETING AND ENRICHING THE SOIL IN ORGANIC MATTER
β-glucosidase (E.C. 3.2.1.21), an enzyme involved in cellulose degradation, plays an important role in the soil organic carbon cycle. Cellulose is the most abundant organic compound in the biosphere so a product of its enzymatic hydrolysis is important as an energy source for soil microorganisms. Since β-glucosidase is very sensitive to different factors, determination of its activity might be helpful in soil quality monitoring. The objective of the study was to assess the effect of various doses of farmyard manure (FYM) and mineral nitrogen on β-glucosidase activity in soil samples taken under winter wheat cultivated in crop rotation systems depleting soil from organic matter (A) and enriching soil in organic matter (B). Soil samples were taken in 2002 from a two-factor fertilization experiment carried out as randomized sub-blocks cropped with winter wheat cultivated on lessive soil. The experiment was located at the Experimental Station of the Institute of Tillage and Soil Science in Grabowo on the Vistula River. All fertilization combinations included FYM (0, 20, 40, 60 and 80 t.ha–1) and nitrogen fertilization (0, 40, 80 and 120 kg ha–1). The activity of β-glucosidase was determined according to Eivazi, Tabatabai (1988). The enzyme activity ranged 3.604-7.041 mM pNP g–1 h–1 in soil samples taken from crop rotation A and between 4.931-7.445 mM pNP g –1 h –1 in those collected from the crop rotation enriching the soil in organic matter. These data were closely related to the applied FYM and nitrogen fertilization doses. Moreover, β-glucosidase activity depended significantly on sampling dates. Enzyme activity was closely connected with soil organic carbon and total nitrogen content, which was confirmed by highly significant correlation coefficients between these parameters (r=0.611-0.770 for C org, and r=0.844-0.912 for N og ; p<0.01 and p<0.001).
Sugarcane residue incubated in soil at different temperatures and nitrogen fertilization
The sugarcane residue deposited on the soil is an alternative source of nutrients, which can serve as a soil conditioner in soil conservation. The effects of sugarcane harvest systems, especially with the residue incorporated into, or left on the soil surface, and the resulting impact on the availability of plant nutrients are little known. The aim of this work was to study the influence of nitrogen fertilization (0 and 120 kg ha -1 of N) and the management of sugarcane residue (surface and incorporated) on the availability of nutrients in soils incubated at three temperatures (20, 25 and 30° C). It was concluded that there is an increase of 6.89 % N in the soil with the sugarcane residue incorporation, compared to the surface management. Total soil N increases were obtained with sugarcane residue, especially when incorporated and associated with nitrogen fertilization. There was no effect of the treatments on soil microbial biomass carbon content (S-MBC), labile carbon (Labile-C), calcium (Ca +2 ), magnesium (Mg +2 ) and phosphorus (P). Potassium is the nutrient that presents rapid mineralization from the residue into the soil. With the addition of the incorporated and soil surface residue there occurred increases in the final K + mineralization of 42.05 % and 11.98 %, respectively.
Temperature effects on lily development rate and morphology from the visible bud stage until anthesis.
Day (DT) and night temperatures (NT) influenced Lilium longiflorum Thunb. 'Nellie White' stem elongation and development rate from the visible bud stage (VB) until anthesis. Plant height increase after VB was a function of the difference (DIF) between DT and NT (DT-NT). Plant height increased 90% as DIF increased from - 16 to 16C. A cubic model described bud development rate as a function of temperature from 14 to 30C. A linear model adequately described bud development rate as a function of average daily temperature from 14 to 21C. Based on the linear model, bud development rate increased 0.05 per day for each 1C increase in average daily temperature. The base temperature for bud development, i.e., the temperature at which bud development rate was 0, was calculated as 3.5C. Greenhouse forcing of vernalized Easter lilies is commonly divided into three phases: I) placement of vernalized bulbs in the greenhouse to flower initiation, II) flower initiation to VB, and III) VB to anthesis (De Hertogh and Wilkins, 1971). Plant morphological development differs during each of the forcing phases (De Hertogh and Wilkins, 1971). Growth during phase I is vegetative and consists of stem elongation and leaf expan- sion. Flower initiation, leaf expansion, and stem elongation oc- cur during phase II. Inflorescence expansion and stem elongation occur during phase III. Lily responses to temperature during phase III differed from those during phases I and II (Wang and Roberts, 1983). Lily development rate, quantified as days to unfold a leaf, is a de- creasing linear function of average daily temperature between 14 and 30C during phases I and II (Karlsson et al., 1988). Lily development rate during phase III is a nonlinear function of temperature (Healy and Wilkins, 1984). The effect of temper- ature on the rate of lily development decreases as DT and/or NT increase during phase III (Rob and Wilkins, 1973; Healy and Wilkins, 1984). Easter lily morphological development is thermomorpho- genie. For instance, internode length increases as the DIF be- tween DT and NT increases (Erwin et al., 1989). In addition, leaf orientation, leaf length, and flower length are also influ- enced by diurnal changes in temperature.