A key issue of applying remotely sensed data to estimate evapotranspiration (ET) for water management is extrapolating instantaneous latent heat flux (LE) at satellite over-passing time to daily ET total. At present, the most commonly used extrapolation methods have the same assumption that evaporative fraction (EF) can be treated as constant during daytime (so-called EF self-preservation). However, large errors are reported by many documents over various ecosystems with the same approach, which indicates that further analysis of the diurnal pattern of EF is still necessary. The aim of this study is to examine the diurnal pattern of EF under fair weather conditions, then to analyze the dependencies of EF to meteorological and plant factors. Long-term flux observations at four sites over semi-arid and semi-humid climate regions in the northern China are used to analyze the EF diurnal pattern. Results show that the EF self-preservation assumption no longer holds over growing seasons of crops. However, the ratio of reference ET to available energy is almost constant during the daytime, which implies the climate factors do not have much effect on the variability of EF. The analysis of diurnal pattern of air temperature, vapor pressure deficiency (VPD), and relative humidity (RH) confirms the assumption that ET diurnal pattern is mainly influenced by stomatal regulation.

As the most important cultural practices for ramie (Boehmeria nivea) production, the single effects of plant density and nitrogen (N), phosphorus (P), potassium (K) fertilization on yield are well documented. To achieve the high yield and quality of ramie fiber, it is principal to quantify the fertilizer dosage for ramie sustainable production. A central composite design (CCD) was adopted with three replications, for a two-year field experiment (2008-2009) in the Yangtze River Valley of China. The aim was to evaluate both the individual and combined effects of plant density and N, P, and K fertilization on yield and fiber quality. The effects of the four factors on yield and quality of ramie cultivar Huazhu 4 were tested. Then mathematical models of the relationship among the four factors affecting ramie production and quality were established and analyzed to optimize the four factors, and used to establish optimum cultivation methods for the elite cultivar suitable to this area of the Yangtze River Valley. Supplements of N (X2), P (X3) and K (X4), and the density (X1) with N (X2) interaction significantly influenced strength in tests of mature ramie. The influence on fiber yield in the two year tests by the four factors ranked as follows: X3>X4>X1>X2. We established the optimization technique attaining yield of 2600 kg ha-1 in the tests as following: density of 28 350-31 650 plants ha-1, and supplements of N, P and K of 363-387, 98.58-105.48 and 280.20- 319.8 kg ha-1, respectively. It was concluded that nitrogen mostly improved plant growth and fiber yield while potassium had discernible effects on fiber quality.