Labile soil organic matter as a potential nitrogen source in golf greens

The loss of fertilizer N from golf greens can be high depending upon management (irrigation schedule, N source, rate and timing of fertilizer application) as well as soil conditions. Although soil organic matter (SOM) is acknowledged as a major source of N and other nutrients, its potential as an N source seems to be neglected in the management of golf greens. The susceptibility of SOM to degradation is one indication of how active a role SOM plays as a nutrient source. An extraction method developed by Olk et al. [Geoderma 65 (1995) 195] distinguishes humic acid fractions by their binding to dominant stabilizing soil cations and separates them into calcium-bound (CaHA) and non calcium-bound or mobile (MHA) fractions. Mobile humic acid is a relatively young, N-rich HA fraction that does not appear to form stable complexes with Ca. The MHA could therefore play a greater role in nutrient availability than CaHA. We determined C and N distributions within SOM extracted from these two HA fractions in 11 golf greens ranging in age from 4 to 28 yr. Because SOM in golf greens is recently formed, and MHA is an N-rich fraction representing an early stage of SOM evolution, we hypothesized that the MHA fraction would account for a larger proportion of soil organic N than CaHA. The amounts of both HA-C and HA-N increased significantly with green age. MHA accounted for a larger proportion (20-27%) of total soil C than CaHA-C (8-14%). MHA was also enriched in N compared to CaHA with consistently smaller C-to-N ratios. Thus, the greater abundance of MHA and its higher N concentration accounted for a larger proportion of soil organic N (24-45%). The equivalence of MHA-N ranged between 250 kg N ha⁻¹ for a 4 yr-old green and 775 kg N ha⁻¹ for a 21 yr-old green. Thus, soils of established greens contain significant quantities of labile SOM rich in N that could through mineralization supply part of the fertilizer N requirement of turf grass. A greater understanding of the dynamics of this resource is needed if we are to manage golf greens for optimal use without negative consequences to the environment.     

氮素形态和配比对麦瓶草（面条菜）产量和营养成分的影响

以麦瓶草（面条菜）为试材,采用基质培方法,研究了不同形态和配比的氮素供应水平对面条菜产量和营养成分的影响。结果表明：在氮素浓度为3.2 mmol?L-1,NO3-－N与NH4+－N的比例为75∶25和50∶50时,面条菜单株产量较高,硝酸盐含量安全,硝酸还原酶活性较强,各项营养成分含量较高,确定其为最佳配比。     

Influence of humic acid on water retention and nutrient acquisition in simulated golf putting greens

Humic substances are frequently applied to creeping bentgrass ( Agrostis palustris Huds.) on golf putting greens to improve turf health and are marketed to enhance nutrient acquisition and possibly aid in retaining water in drought prone environments, but information on the role of humic substances in increasing soil water retention is limited. Additionally, it is difficult to separate the beneficial effects of nutrients and other ingredients added to commercial humic formulations from the effects of the pure humic substance. In our study, pure humic acid, tannic and citric acids were added to simulated creeping bentgrass putting greens. The organic acids were applied at normalized carbon rates of 250 mg C per litre by watering solutions through an automated irrigation system. Volumetric water content (VWC) and irrigation frequency, shoot and root growth, and tissue nutrient concentration of the turf were measured. None of the organic acid treatments improved water retention in the simulated greens. The humic acid-treated greens required more frequent irrigation than the untreated greens indicating that they were drying out more quickly. In addition, the addition of humic acid did not result in an increased tissue concentration of nutrients in the creeping bentgrass, top growth or dry shoot mass compared with the other treatments. However, creeping bentgrass root length was greater in the greens treated with humic acid compared with the untreated control.     

Simulation of putting-green soil water dynamics: Implications for turfgrass water use

Results from a field experiment examining soil water fate within U.S. Golf Association (USGA) putting greens were used to examine the validity of a water flow simulation model. The experiment used six different sandy root zones each with depths of 300 mm overlying a 100 mm thick gravel layer. Data collected over two growing seasons consisted of measured rainfall, irrigation, drainage volume, and soil water contents; and calculated turfgrass evapotranspiration (ET). Turfgrass rooting was measured at the end of each growing season, and water retention curve and saturated hydraulic conductivity measurements were conducted at the end of the study. For each root zone treatment, HYDRUS-2D (H2D) was calibrated using a subset of the experimental data and then validated by comparing observed and predicted water contents at 76, 152 and 229 mm depth and over both growing seasons. Model efficiency (E) ranged from 0.33 to 0.78; Mean Absolute Error (MAE) ranged from 0.012 to 0.024 m³ m⁻³; and Root Mean Square Error (RMSE) ranged from 0.015 to 0.028 m³ m⁻³, for the six treatments and both years. Also, RMSE values were at best slightly larger than and at worst twice as large as the mean standard deviation values of replicate measurements. Thus, H2D simulation performed reasonably well in describing the water content results of the field study. The calibration results provide evidence of hysteresis in water retention where water retention properties from the field appear to follow the sorption or wetting curve as compared with the laboratory measurements following the desorption or drying curve. This suggests that standard laboratory measurements of water release would not precisely predict water retention behavior in the field and over estimate water storage of these capillary barrier soils. The validation results provide evidence for turfgrass use of perched water held within these profiles, even though turfgrass rooting is shallow and water storage principally occurs deep within the root zone. Thus, the perched water of USGA putting greens should serve reasonably well as a water reservoir for subsequent turfgrass use, allowing for water conserving irrigation practices that makes use of this stored water.     

小菘菜异源胞质雄性不育系CMS08-6的选育

用大白菜异源胞质雄性不育系CMS22-3为母本,不同小菘菜自交系为父本,通过连续几代回交,最终选育出小菘菜异源胞质雄性不育系CMS08-6.该不育系具有生长发育正常、抗病、农艺性状优、配合力好等特点,利用CMS08-6配制的组合CMS08-6×87-6在示范生产上表现较优良.     

Biomass yield and composition of sweetpotato grown in a nutrient film technique system

Sweetpotato cultivar TU-82-155 grown in a nutrient film technique system and separated into foliage, tips, fibrous, string and storage roots at harvest had a total dry biomass of 89.9 g per plant with 38.4% inedible portion. Tips and storage roots, the traditional edible parts, were analyzed for dry matter, protein, fat, ash, minerals (Ca, Fe, K, Mg, Na, Zn), vitamins (carotene, ascorbic acid, thiamin), oxalic and tannic acids, and trypsin and chymotrypsin inhibitors to determine their nutritional quality. Water soluble matter, minerals (Ca, Fe, K, Mg, Na, Zn), cellulose, hemicellulose and lignin concentrations in the edible and inedible parts were obtained to provide information needed for the selection of appropriate bioconversion processes of plant wastes into food or forms suitable for crop production in a controlled biological life support system.     

Changes in kale (Brassica oleracea L. var. acephala) carotenoid and chlorophyll pigment concentrations during leaf ontogeny

There has been recent market interest in “baby” salad greens. However, little information exists on the nutritional differences between immature “baby” greens and produce traditionally sold at the fully mature stage. Kale (Brassica oleracea L. var. acephala D.C.) contains high levels of lutein and β-carotene, which possess important human health properties. Kale was grown in a controlled environment and pigments were measured in young (<1 week), immature (1–2 weeks), mature (2–3 weeks), fully developed (3–4 weeks) and senescing (>4 weeks) leaves using high-performance liquid chromatography (HPLC). Significant differences were observed for all pigments during leaf development. Pigment accumulation followed a quadratic trend, with maximums occurring between the 1st and 3rd week of leaf age. The highest concentrations of lutein measured 15.1 mg/100 g fresh mass and occurred in 1–2 week old leaves. The remaining pigments reached maximum levels at 2–3 weeks (β-carotene at 11.6 mg/100 g; chlorophyll a at 251.4 mg/100 g; and chlorophyll b at 56.9 mg/100 g fresh mass). Mature fully expanded kale leaves accumulated higher carotenoid concentrations than immature or “baby” leaves, with senescent leaves having the lowest carotenoid concentrations. Harvesting kale leaves at a mature stage of development resulted in maximum carotenoid values. Cultural management practices that increase carotenoid concentrations would be expected to improve nutritional quality for fresh markets.     

Molecular identification and pathogenicity of Rhizoctonia solani and Pythium spp. associated with damping-off disease on baby leafy vegetables in Greece

In the last years, leafy vegetables cultivated as baby leaves have been established in the market and have attracted the interest of consumers throughout the world. During the growing seasons of 2019 and 2020, 97 isolates of Rhizoctonia solani and 112 isolates of Pythium spp. were obtained from baby leaf vegetables exhibited damping-off symptoms. Representative isolates of R. solani from each surveyed plant species were characterized using sequence analysis of the internal transcribed spacer (rDNA-ITS) region. Isolates were identified as belonging to four anastomosis groups (AGs): AG2-1, AG-IB, AG4-HGI and AG4-HGIII. AG4-HGI was the most prevalent group and phylogenetic analysis showed that the isolates were distinctly separated according to their AGs. Pathogenicity among the four AGs on 23 plant species varied considerably, from not susceptible to highly susceptible, while, in general, AGs did not exhibit host specificity. Furthermore, a total of 112 Pythium spp. isolates were obtained. The ITS region and the cytochrome oxidase II (coxII) gene were amplified, and three Pythium spp. were identified (P. ultimum, P. aphanidermatum and P. sylvaticum), which were used further for maximum-likelihood phylogenetic analysis. The pathogenicity of representative isolates was assessed in vitro and in vivo on 10 plant species. In general, all three tested Pythium spp. were virulent when used in vitro, while P. ultimum was the most virulent in vivo. This is the first comprehensive study aimed at determining the occurrence of specific R. solani AGs and Pythium spp. derived from baby leafy vegetables exhibiting damping-off symptoms in Greece.