What factors affect the sweetness and sourness of grapefruit?

(1) Climatic conditions The annual average temperature in the country of origin is 17.5℃, the extreme high temperature is 4.5℃, the extreme low temperature is -9.2℃, the frost-free period lasts for 238 days, the annual precipitation is 1725.3 mm, and the annual sunshine is 1898.6 hours. Grapefruit has stronger tolerance to low temperature than sweet orange, orange orange and satsuma orange. (2) Topography and topography Grapefruit is not strict with topography. It can be planted in plains, beaches, hills, low mountains and mountainous areas with an altitude of less than 5 meters and a slope of no more than 2 5 degrees. Grapefruit is of better quality. When planting pomelos in mountainous areas, we should take advantage of the phenomenon of "inversion layer" caused by radiation and heat dissipation in winter to avoid planting in the low valley of basin bottom where cold air is easy to accumulate, so as to prevent freezing injury. The mountainous area near the big reservoir often forms a microclimate favorable to grapefruit, which is especially suitable for development. (3) Grapefruit is not strict with the soil, and the soil pH value should be 5.5-6.5. Alluvial soil, red and yellow soil, purple sand soil and vegetable garden soil can be planted as long as the soil layer is deep and the drainage is good. Sandy loam is the best soil quality. The soil is sticky, the drainage is not smooth, and the ventilation is poor, which is extremely unfavorable to the growth of grapefruit and is easy to be damaged by freezing.