de Bie, Kees 
  
  
300 
     
  
[3 Sunshine duration in Chiang Mai 
250 - (h/month; 1954-80) 
Sunshine duration 
200 4 = Precipitation in Phrao 
(mm/month; 1952-85) 
150 4 
= _ET-pan in Chiang Mai 
100 - (mm/month; 1965-80) 
  
  
ies Humid period 
50 4 
  
  
  
  
  
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 
Figure 2. P - ETpan diagram for Phrao. 
3. Study method 
In 1993, "old" (present in 1977), “young” (present in 1984), and “recently 
established” orchards (since 1984) were sampled, i.e.: hills 16x, footslopes 20x, 
and terraces 28x (total of 64). This number represents about 50% of the total 
number of orchards present in 1984 (Figure 1). The availability of farmers strongly 
influenced the selection of sites; the intention was was to sample an equal number 
of orchards on each terrain unit, with a minimum of 5 orchards in each age 
category. Collected data covered every aspect of operation sequences followed 
and a set of easy to measure land properties. All data were entered in the Land 
Use Database. In a spreadsheet, for applicable parameters, the query results 
were generalized to achieve a reduced number of nominal classes. Next, site- 
specific soil data were added and categorical data normalized. The data were then 
screened with descriptive statistics and used for model estimation. Next, the 
contribution of individual constraints to the overall yield gap was estimated. 
4 Descriptive statistics 
Most orchards surveyed consisted of a mix of mango (Magnifera indica L6 
lychee (Litchi chinensis Sonn.), and longan (Dimocarpus longan Loureiro) trees. 
Mango was found in 49 of the 64 orchards surveyed, i.e. in all orchards on hills 
and footslopes and in 13 of the 28 orchards sampled on terraces. Footslopes had 
relatively more pure mango stands and terraces had relatively fewer mango trees 
(Table 1). Tree counts revealed that mango trees make up 34, 42 and 23% of 
orchards on hills, footslopes and terraces respectively. Orchard sizes were 
inferred from aerial photographs flown in 1984 and from step counting in the field 
and a Spot-Pan image of February, 1993. They varied from 0.12 to 8.0 ha 
(average of 1.6 ha). 
  
5 
6 Systat v.7.0.1 software (© 1997 SPSS Inc.). 
There are more than one hundred local mango varieties in Thaïland; prominent ones are Ok-Rong, 
Nangklangwan, Rad, Pimenmun, Kwiewsawoey, Namdokmai, Fahlan, Petchbanlad, Chackhuntip, 
and Salaya (Subhadrabandhu 1986). 
  
  
324 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.