Physiological Studies On Water Requirements Of Potato Plant (solanum Tuberosum):

Magdi Abd El-ghafar Ali

The present investigation was carried out at El-QanaterHorticultural Research Station, Kalubia Governorate, duringthe two successive seasons 1989/1990 and 1990/1991. The mainobjective of this work is to study the effect of water regimeand growth regulators on growth, yield, water use andchemical composition of potato plant (Solanum tuberosum). Forsuch target two field experiments were carried out. Thetreatments of the first experiment were as follows:A: Irrigated according to the local farmer practice.D: Irrigated at 0.5 bar.e; Irrigated at 1.0 bar.0: Irrigated at 1.5 bars.E: Irrigated when 50% of the available soil moisture isdepleted as estimated by modified Penman method.The treatments of the second trial were as thefollowing: A: Control.B: Sprayed with GAs at a concentration of c: Sprayed with GAs at a concentr ation of 200 ppm.OJ Sprayed with ece at a concentration of 1000 ppm.E: Sprayed with CCc at a concentration of 2000 ppm.Growth regulators were sprayed when plants aged 45 and60 days. A complete randomized block design was used for bothexperiments, in the two seasons, and in fall and summerplantations. Agricultural practices were carried outaccording to the usual methods being adopted for such crop.The variety Konder was used in the 8 experiments.The most important results induced investigtation could be summarized as folloWS:from this A. EFFECT OF WATER REGIME1. Increasing water stress resulted in decreasing plantheight significantly. 2. Potato plant directed its growth in fall plantation for producing shorter plants with higher number of branches,while in summer the plants are taller with less number of branches. Also, it can be noted that maximum values of branches/plant were produced from the wet treatment3. Leaf area/plant increased gradually from emergence ~othe last sampling date (80 days after planting) in summerplantation, while a slight decrease in leaf/area was observedat the age of 80 days. The wet treat_ent has the highestvalue of leaf area per plant.4. Maximum period of dry matter accumulation by leaves was from emergence up to 50 days in fall, while in summer it was from 50 to 65 days. In both plantations the grand period of dry matter accumulated in stems was found to be from emergence up to 50 days. The highest proportion of dry matter accumulation in tubers falls in the period from 50 up to 80 days after planting. Dry matter of the whole plant increased gradually from planting to the last sample. It was noticed that prolonged irrigation intervals decreased the accumulation of dry matter. This may prove the importance of maintaining a high level of soil moisture for better growth. 5. The highest values of eithertubers were obtained from treatments ThUS, it can be noted that maintaining level produces larger tubers.length or width of irrigated freqently.high soil moisture6. Tuber index or the ratio between length and width wasnot affected significantly by water deficit. However, resultsindicate that low or moderate stress increased the values oftuber index. On the contrary, severe soil moisture stressresulted in decreasing such value.that potato tubers are somewhat These results indicate spherical in shape whengrown under low soil wa~er, while under high soil mois~urelevel, the tuber length was much more than its width.7. Results have shown that mainly controlled by geneticsenvironmental conditions. number of tUber/plantand to less extent is by B. Maximum tuber yield/plant was scored from the wet level (0.5 bar) followed by medium soil moisture regime (1.. 0 bar and farmer practice). However, the lowest value wasattained from dry treatments (1.5 bars and 50% modifiedPenman). It is worthy to mention that tuber yield/plant wasfound to be greater in fall plantation than that obtainedfrom summer season.9. Average tuber weight data showed that it was higherin fall compared with summer plantation. Regarding the effectof water regime, similar results were obtained as those oftuber yield/plant.10. Potato plants imposed to severe water stress, had ahighet1,-tober;dry.,lDatterpercentage cOlDpared with those plantsirrigated frequently. 1. Water deficit has no obvious effect on tuber specific weight and/or total soluble solids either in fall orsummer plantation and the values were about the same. 12. The data indicate that for maximum tuber yield of potato, irrigation water should be applied at 0.5 bar soilmoisture tension. However, more than that level, the yielddecreased significantly. It is worthy to mention that thevalues obtained from the medium soil moisture stress and thefarmer practice are about the same. This means that theEgyptian farmers irrigate their fields at moderate stresswhich affects the final tuber production.13. Fall plantation was superior in producing largertubers in size compared with those produced from summerplantation. With regard;s to the effect of water deficit ontuber size, data had shown that high and medium soil moisturelevel produced the highest percentage of larger tubers. Onthe contrary, severe water deficit did result in decreasingthe percentage of medium and larger tubers, while increasedthe percentage of smaller tubers. These results mean thatmaintaining a high soil moisture level through the growthperiod of potato improved the production of tubers byproducing larger tubers.14. Seasonal water consumptive use by potato variesbetween 300.4 mm and 419.3 mm for fall planta~ion, while forsummer ~he values ranged from 443.4 mm to 626.9 mm. Thevariations are mainly due to climatic condi~ions and to ~heirrigation treatments. The highest water use value wasattained under low water deficit. Increasing soil moisturestress by prolonged irrigation intervals resulted in decreasing water consumption. 15. Daily evapotranspiration rates reached its maximumvalue when potato plants aged 90 days in fall and 75 days insummer plantation. Such period is considered as the stage oftuberization, hence plant needs more water as the tubersincreased in size and weight.16. Crop coefficient was estimated using Penman formulaand actual evapotranspiration rates. The values were low atthe initial stage, then increased to reach its maximum valueat mid season stage. Such period is considered the peackwater demand by potato (the period of tuberization). A sharpdecrease in crop coefficient was observed at the end of theseason. Seasonal crop coefficient was found to be 0.75 and0.77 for summer and fall plantations respectively.17. Potato plant extracts about 80% of its moistureneeds from the upper foot. This may prove that potato plantis relatively sensitive to soil water deficit and has to beirrigated frequently. lB. Water use efficiency values experssed as kg. dry matter/feddan/one cubic meter of consumed water, were higherin fall plantation more than in summer one. It can bementioned that fall plantation is preferable from stand pointof either production or water use efficiency. Increasing soilmoisture stress decreased the value of water use efficiency,this was true in both seasons, and in fall and summerplantations.19. Efficiency of water use data, expressed as kg oftuber yield/feddan/m3 of water consumed, revealed that thevalues of fall plantation were higher than those of summercultivation. With regards to the effect of soil moisturestress on water use efficiency, data had shown that itdecreased as water deficit increased. The reverse trend wasfound to be true.20. It can be concluded that maintaining a high soilmoisture level not only increases tuber production but alsoallows potato plant to use water more efficiently. Theprevious results may lead to the conclusion that potato plantis more sensitive to water deficit and this is morepronounced in summer plantation than fall one.21. Nitrogen content of potato leaves and stems increasedgradually from the first sample up to 65 days, thendecreased. As for nitrogen content of tubers, results showedthat it decreased by time from the first sample to the lastone. Nitrogen was decreased by increasing soil moisturestress. As for phosphorus concentration, data showed asimilar trend to that observed with nitrogen. However,potassium concentration seemed to increase by water deficit.22. A gradual increase in total sugars was observed fromthe first period <50 days} to the second stage (65 days), inleaves and stems. However, the tUbers sugar content decreasedgradually from the first sample to the last one. The valueswere higher in fall than in summer plantation, in leaves andstems. 23. Results showed a gradual increase in totalcarbohydrate from the first sample up to 65 days, thenslightly decreased. This pattern is true in leaves and stems,while the reverse is clear in tubers. Water deficit has anegative response upon the accumulation of totalcarbohydrates. 24. Data indicate that different chloroplast pigments increased with advancing age. The rate of increase inchlorophyll exceeds the rate of carotenoides. Generally,chlorophyll (a + b) concentration is less under summerplantation compared with fall. However, carotenoides (c) ishigher in summer than fall season. The ratio between albseemed to be similar under various irrigation treatmentswhich indicates that any decrease in chlorophyll (a) by waterdeficit is accompanied by a similar decrease in chlorophyll (b). However, the ratio (a + b)/c was decreased by water deficit.