Numerous models have been developed for calculating optimum decision rules for nitrogen fertilization based on remote sensing techniques. New technologies related to digital image analysis may provide an alternative method to estimate nutrient status faster and more efficiently than current techniques. A series of field studies was conducted to determine the applicability of digital image analysis for nitrogen demand estimates in broccoli plants. Digital images were taken under constant light conditions in various wavelength ranges (380–1300 nm) using a digital imager. Images were processed for the parameters and in the color system. The image analysis showed a close correlation between the nitrogen status of broccoli plants and the parameter of the color system especially in the wavelength ranges and nm. The relationship between nutrient concentration in leaf dry matter and the parameters was used to determine the N fertilizer demand within the cultivation period. Estimated N amounts were applied as top dressing four weeks after setting and were 100 kg lower than the standard fertilizer rate. Calculated N balances indicated a total uptake of applied N amounts in the image-based N treatments without considerable yield loss. Thus, digital image analysis proved to be an effective means of determining nitrogen status and adjusting fertilizer applications to preserve or enhance crop quality and yield considering sustainability.
The expansion of intensive vegetable production systems exacerbates ongoing resource degradation in China's Hebei province. There is an urgent need to develop and disseminate more sustainable vegetable production systems. Intercropping, the simultaneous cultivation of two or more crops on the same field, is widely practiced in the region. Intercropping can use environmental resources more efficiently and is therefore considered to generate high and stable yields with lower inputs. Until now, scientific literature on vegetable intercropping in China is non-existent. To identify prevailing vegetable intercropping systems, a qualitative inquiry was conducted in southern Hebei province. Researchers, extensionists and farmers were interviewed on the occurrence, methods, potentials and constraints of vegetable intercropping. Furthermore, semi-structured in-depth interviews were conducted to examine the farmers' underlying motives and concepts and to determine the origin and distribution of the systems. The investigations revealed a huge variety of sophisticated systems being practiced in southern Hebei. Apart from pure vegetable intercropping systems such as spinach–garlic, especially maize–vegetable and cotton–vegetable systems are widespread. The systems are developed by the farmers themselves and disseminated by the state extension service. Apart from the benefits of plant health, the optimal use of limited land resources is the main reason for farmers to exercise intercropping. However, with the ongoing mechanization and labor force reduction in the agricultural sector, a great part of the intercropping systems, which demand a high input of manual labor, are prone to extinction in the long run. Recent research in China focused purely on agronomic advantages of intercropping, neglecting the linkages between the socio-economic developments and farmers' decisions in the field. To overcome this dilemma and to maintain the traditional and sustainable intercropping systems, we conclude that only an integrative research approach that involves various stakeholders from the beginning is able to adjust the intercropping systems to future demands.
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