Effects of nitrogen (M) and water supply on grapevine leaf transmittance and canopy reflectance were studied over 2 years (2009)(2010) in two vineyards planted with cvs. Cabernet Sauvignon and Xinomavro (Vitis vinifera L.) located in northern Greece. Three N (0, 60 and 120 kg ha -1 ) and two irrigation (irrigated at 70 % of crop evapotranspiration and non-irrigated) treatments were managed in triplicate in randomized blocks. Measurements with two transmittance-based chlorophyll meters (CM: SPAD-502 and CCM-200) and two active canopy sensors (Crop Circle ACS-210; amber band and Crop Circle ACS-430; red and red edge bands) were conducted on four and two growth stages, respectively. Fertilization increased leaf N and chlorophyll concentrations, as well as CM readings and vegetation indices. The CCM and SPAD values did not vary across growth stages and better estimated leaf N and chlorophyll concentrations in Cabernet Sauvignon than in Xinomavro. The SPAD readings provided better predictions of leaf N concentration. The vegetation indices of the ACS-430 sensor correlated with leaf N and chlorophyll concentrations and dormant wood in Cabernet Sauvignon; the red edge-based indices were generally more efficient than the red-based indices. Consistent relationships were observed for all ACS-430 indices with yield and for red edge-based indices with total phenols early in the season for both vineyards. The correlation between ACS-210 sensor indices and vine properties was low. These results showed that the two technologies examined could provide information on grapevine performance early in the season but have limitations that may restrict their use in vineyards because the acquired relationships were not consistent across vineyards and instruments.
Th e eff ects of sludge application on soil properties and cotton (Gossypium hirsutum L.) response were investigated in an Inseptisol in central Greece. Digested sludge was incorporated in the 0 to 15 cm soil depth at rates of 10, 30, and 50 Mg ha -1 , and repeated for four consecutive years. Sludge treatments were compared to an inorganic fertilizer application and an untreated control in a completely randomized design with four replications. Sludge application increased soil organic matter, associated nutrients and improved physical properties. However, soil electrical conductivity increased with increasing sludge application to levels that may aff ect growth of salt-sensitive crops and warns against long-term application that may impair essential soil functions. Th e multifold increase of Olsen P and nitrate N beyond crop needs is a reason of concern for surface runoff and nitrate leaching below the root zone at the higher sludge application rates. Sludge application of 10 Mg ha −1 was suffi cient to improve soil chemical properties with less risk of water contamination. Cotton responded to sludge application by increased nutrient uptake and yield, which indicated that sludge could replace inorganic fertilizer needs even at the lower application rate. However, fl uctuations of nutrient uptake and yield between growing seasons were of greater magnitude than those caused by sludge application. Multiple regression analysis revealed that P uptake was the major limiting factor for determining cotton yield.
Soil quality changes resulting from repeated or single injection of liquid municipal sewage sludge were evaluated in terraced cropland in eastern Nebraska, USA. Differences in soil properties among sampling locations were explained primarily by two factors, landscape position and sludge injection. Selected chemical properties (pH, EC, NO 3 ±N) did not generally differ between landscape positions, but soil organic matter (organic C and N) and microbial activity indices (soil respiration, biomass N, available N, mineralization and nitri®cation rates) were more sensitive indicators of change. Values of these indicators generally increased down-slope from the upper terrace to the grassed waterway on a west facing slope. A probable similar pattern on the east slope was obscured by repeated application of sludge. Single or repeated (long-term) sludge injection increased the readily decomposable organic matter, ammonium-and available-N in soil (0±30.5 cm depth). These changes stimulated soil microbial activity as evidenced by increased basal respiration, net mineralization and nitri®cation rates. Consequently, nitri®cation of ammonium-N was re¯ected in soil chemical properties as increased soil nitrate-N (to levels that were more than two times higher than suf®ciency levels for corn) and EC and by decreased pH. In-®eld measurements detected changes in physical properties such as a decrease of in®ltration rate caused by sludge injection and soil compaction as a result of traf®c operations. Differences between the sites of single and repeated sludge injection were found in soil pH, ammonium-N, organic matter and microbial activity. Recent sludge injection resulted in higher ammonium-N concentration and higher microbial activity in soil, and repeated sludge injection resulted in lower pH and in greater organic matter content. Regardless of these differences in soil properties between the sites of single and repeated sludge application, the overall changes that were caused by sludge injection had both positive and negative effects on soil quality and the sustainability of this management practice. Increase of organic matter content and biological activity improved soil fertility, but excessive amounts of ammonium salts contained in liquid sludge resulted in soil nitri®cation, excessive nitrate formation and acidi®cation. These processes reduce soil productivity, increase the risk of ground-and surface-water contamination and pose a threat to plant and animal health. #
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.