Effect Of Fertigation On Soil Environment And Cucumber Growth In Protected Cultivation

The solar greenhouse is one of the major horticultural facilities in the Northern China. However, excessive irrigation and fertilization are commonly practiced in the solar-greenhouse production systems. Moreover, conventional interval fertigation is still common in intensive vegetable production systems in China, Consequently, the nutrient concentration in the root-zone soil may be in excess of plant requirement for growth on the first day after fertigation, and then decreases gradually to reach deficit levels before the day preceding the next fertigation event, and eventually inhibit crop growth and development and soil quality. Therefore, there is a need for ensuring water and nutrient in root-zone soil appropriate and stable to reduce adverse effects caused by their fluctuation on crop growth under intensive vegetable management practices. Firstly, a greenhouse study for two years was therefore conducted to investigate the effect of different fertigation methodes on root growth, fruit yield of cucumber (Cucumis sativus L.). The treatments included conventional interval fertigation, optimal interval fertigation and optimal daily fertigation. In additon, it was reasearched that effect of different fertigation methodes on soil nutrients and microbial properties to evaluate soil quality. Lastly, a hydroponics experiment was therefore conducted on cucumber seedlings under four treatments included maintaining appropriate and stable nutrient concentration (CK), maintaining high and stable nutrient concentration (HH), decreasing gradually nutrient concentration from high level to low level (HL) and increasing gradually nutrient concentration from low level to high level (LH), in order to demonstrate effect of stable or fluctuant application of nutrients under high salt concentration on root occurrence, growth and development of hydroponic cucumber during vegetative period. The main results were listed as follows:1. Generally, although soil under the treatment optimal interval fertigation received much lower fertilizers than soil under conventional interval fertigation, the treatment optimal interval fertigation did not statistically decrease the economic yield and fruit nutrition quality of cucumber when compare to conventional interval fertigation. In addition, the treatment optimal interval fertigation effectively avoided inorganic nitrogen accumulation in soil and significantly (P<0.05) increased the partial factor productivity of applied nitrogen by88%,209%75%and146%in four cropping seasons, respectively, when compared to conventional interval fertigation. Although soils under the treatments optimal interval fertigation and optimal daily fertigation received the same amount of fertilizers, the treatment optimal daily fertigation maintained the relatively stable water, electrical conductivity and mineral nitrogen levels in surface soils, promoted fine root (<1.5mm diameter) growth of cucumber, and eventually increased cucumber economic yield by8.1%,7.6%,0%and34.6%in four cropping seasons, with accordingly increasing partial factor productivity of applied nitrogen and irrigation water use efficiency, when compared to the treatment optimal interval fertigation. These results suggested that optimal daily fertigation is a beneficial practice for improving crop yield and the water and fertilizers use efficiency in solar greenhouse.2. Based on data from cropping seasons, although the treatment optimal interval fertigation can effectively avoid soil acidification and excessive accumulation of sality and nutrients, there was a lower soil organic mater content, which was possibly unfavorable to enhance soil fertility for a long time, when compare to conventional interval fertigation. There was no significant difference in soil contents of organic matter and nutrients betweenm optimal fertigation treatments. In additon, there were no significant difference in soil microbial carbon and microbial community genetic and functional diversities among three fertigation methodes treatments, based on data acquired by using DGGE and Bilog technologies, respectively. These resluts sugggestted that all three fertigation methodes can prevent soil quality from decline in the short time, but it needed to be further demonstrated whether there was significant difference under three fertigation methodes for a long time.3. Analysis of variance showed that compared with the treatment CK, the treatment HH strongly repressed root length but promoted leaf nitrogen content due to high nutrients concentration and higher root NRT2gene transcription expression, and further rised leaf contents of chlorophyll-a. However, it simultaneously reduced leaf intercellular CO2concentration, ultimately leading to no significant leaf dry weight but decline of leaf water content, with displaying very low nutrient use efficiency and little death of leaf edge cell. In addition, the fluctuation treatments (i.e. HL and LH) regulated contradictory relations between leaf intercellular CO2concentration and leaf contents of chlorophyll-a by increasing root hair density and length as well as rising root NRT1.1and NRT2gene transcription expression when nutrients concentration is low, to guarantee leaf normal photosynthesis and growth, compared to the treatment CK, vice versa. These results indicated that plant root had some adaptability to the changes of salt concentration in the enviroment.