| Water storage pit irrigation method is a three-dimensional deep irrigation method proposed by Professor Sun Xihuan in 1998. Its soil water distribution is different from that of other irrigation methods. Affected by the distribution of soil moisture, the root growth distribution of apple trees under water storage pit irrigation also has its own characteristics, which directly affects the absorbing capacity of tree roots and the moisture migration of orchard SPAC system. This paper, by taking three section stock dwarf type red Fuji Changfu No.2 as materials, six irrigation treatments(T1, T2, T3, T5, T6 and T7) were designed to measure the water potential of apple orchard SPAC system and the yield of each treatment, surface irrigation(D) as comparison, and draws the following main conclusions:(1) Studies on the characteristics of water potential variation of apple orchards SPAC system: ①the leaf water potential of the same tree but of different heights turns out to be low part > central part > high part, decreasing gradually from low part to high part, while that of the same branch but of different heights be the highest in the central part, and lower in low and high parts; ② the daily variation of soil water potential is not obvious, with eachtreatment slightly fluctuating within the scope of a fixed value, while the variation of leaf water potential and stem water potential is characterized by decreases and then increases. The highest value appears around 7:00 in the morning, and then begin to decline afterwards and the lowest value in a day appears around 13:00, and then slowly began to rebound, but pick up less than the value at 7:00 in the morning. The atmosphere water potential is also characterized by decrease and then increase, the maximum level in a day appearing around 6 o’clock in the morning, soon falling to the lowest level of the day, and the atmospheric water potential gradually recovering after 18:00,and restoring to the level of early in the morning; ③the dawn soil water potential in the whole growing period fluctuates slightly, the leaf and stem water potential is approximately in the shape of parabola, that is, initially the water potential is low, then gradually increases, and decreases slowly after mid September, and the dawn atmospheric water potential is lower in May and October, higher in July and August with the whole variation in the whole growth period showing a "n" type; ④the daily variation of water potential gradient from soil to leaf shows the obvious trend of being low in the morning and evening and high around noon, the dawn water potential gradient in the whole growth period is characterized by decrease and then increase; the water potential gradient from leaf to atmosphere mainly depends on the atmosphere water potential, which tends to reduce gradually in the day; the dawn water potential gradient in the whole growth period is characterized by decrease and thenincrease and the energy of water within the SPAC system is mainly consumed on the blade-atmosphere link;The fruit yield of T2 treatment unit irrigation amount is 13.14g/L, which is much higher than other treatments;⑤the soil volumetric moisture threshold under the condition of ground irrigation(D)is about 14%, whose corresponding soil water potential is about-0.25 MPa, to ensure that 44.5% of apple orchard soil moisture above the field capacity in the production practice; when the soil volumetric moisture under water storage pit irrigation gets down to 15.3%, which hasn’t reached the threshold, the threshold is expected to be lower than that of ground irrigation due to its advantage of water retention.(2) Studies on the relationship between the water potential in apple orchard SPAC system and its influencing factors: ① soil water potential and soil volumetric moisture are positively correlated with each other. Their correlation can be represented by ψs = aθv + b, where a, b are empirical parameters; ②from comprehensive analysis of all the environmental factors, atmospheric temperature and atmospheric relative humidity, and solar radiation are all the main environmental factors which affect the variation of leaf water potential;path analysis shows that in May atmospheric temperature(Ta) is the biggest influential factor, with relative atmospheric humidity(RH) and solar radiation(R) following in turn; in July and September relative atmospheric humidity(RH)is the biggest influential factor with atmospheric temperature(Ta) slightly second and the net solar radiation(R) effect the weakest; the direct effect of netsolar radiation on leaf water potential is less than its indirect effect via the atmospheric temperature and relative humidity, that atmospheric temperature and relative humidity are main environmental factors which directly affect apple leaf water potential variation, and that leaf water potential variation can predicted by atmospheric temperature and relative humidity; ③ the daily variations of stem water potential and runoff rate are both characterized by an opposite trend: stem water potential decreases and then increases while runoff rate increases and then decreases, both of which possess good negative linear correlation. ④ dawn leaf water potential increases with the increase of soil water potential, the two show a quadratic parabolic relationship, which is a good correlation; leaf water potential and stem water potential show good positive linear correlation;leaf water potential and atmosphere water potential also show a positive linear correlation.( 3) Combined with the leaf water potential and stem water potential,water potential gradient change characteristics and fruit yield, T2 treatment is the optimal irrigation lower and upper limit, that,the 60% to 90% of the water holding rate of the field can be used to guide the production practice;the new shoots’ vigorous growing period is the critical period of the apple tree water requirement.water shortage in this period will cause irreversible physiological damage to the normal growth of apple trees in a certain degree,special attention should be paid to the irrigation during this period in the production practice. |
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