B. Bravdo

A model to simulate response of plant stomata to environmental conditions

Abstract In order to simulate plant transpiration under different field climatic conditions we have developed and verified a semi-empirical model for predicting the stomatal response to solar global radiation, leaf temperature, vapour pressure difference between the leaf and ambient air, ambient air CO2 concentration and soil water potential. The transpiration and the stomatal relative conductance of a Nicotania Tabaccum var “samsun” plant leaves were measured in a laboratory apparatus and compared to those predicted by the model: good agreement was obtained between them for the different investigated cases. The model was incorporated in a numerical greenhouse microclimate model and its effects on the canopy microclimate are discussed here.

Soil moisture and root distribution in an apple orchard irrigated by tricklers

SummaryThe soil moisture distribution at different distances from the water source in a high-yielding apple orchard planted on a 60-cm-deep heavy basalt soil underlined with gravel was studied. The soil water content was determined in three irrigation treatments which differed in discharge rates, distances between the tricklers on the lateral, and frequencyof application of an equal amount of water. The determinations were made several times during the wetting and drying processes in one irrigation cycle of each treatment. The roots of the trees perpendicular to and along the trickler line were counted in the soil profile. The results showed that the soil moisture and root system distribution covered a wider area when irrigated twice a week with 8 1/h tricklers rather than by irrigating every day or once a week with 4 1/h tricklers. Every day compared with once a week irrigation caused an appreciably narrower soil moisture distribution but a quite similar root distribution pattern. The soil-moisture-saturated level in the soil profile in all treatments, in the area under the trickler, caused water loss by drainage while irrigation continued. The loss was estimated to be 17% of the water applied. A pulsed irrigation was assumed to decrease this drainage loss by trying to supply the water in pace of the plant consumption.

The effect of irrigation and crop load on stem water potential and apple fruit size

SummaryThe effect of irrigation rate under various crop loads on the fruit size of apple (Malus domestica Borkh cv. Golden Delicious) was investigated in three field experiments in 1993–1995. Durin...

Control of root size and root environment of fruit trees for optimal fruit production

Abstract Recent development in technologies of irrigation and fertilization enable us to control root size and environment under field conditions. Low volume irrigation and fertilization affects root size and rate of rootlets production and consequently vegetative and reproductive processes of whole plants. The mechanisms involved seem to include growth regulators production at the root apexes and their translocation to the shoots. Field experiments in a few species of deciduous trees and citrus, showed that root systems are very flexible and can adjust to low volume irrigation irrespective of age or size of the trees or stage of development. Root restriction under field conditions was found to cause precocity, increase productivity and reduce the size of the trees. A greater number of trees per unit land can be grown without reducing light penetration which is the most important factor affecting physiological processes controlling fruit bud differentiation, such as assimilate translocation, photosyntheti...

Effect of irrigation regimes on trunk and fruit growth rates, quality and yield of apple trees

SummarySix irrigation treatments were applied to an apple orchard. The treatments consisted of replenishing the soil water deficit at the 0-60 and 0-120 cm layers according to predetermined available water content. The seasonal patterns of trunk and fruit growth and of fruit drop were studied. It was found that the final volume of fruit was linearly related to the number of days to which the trees were subjected to above and below 30% available water in the 0-60 cm layer. Fruit firmness and soluble solids content were reduced by frequent irrigation. These reductions were found to be due both to a direct effect and to an indirect effect through the increase in fruit size due to frequent irrigation.

Photosynthesis, transpiration and stomatal resistance to gas exchange in tomato plants under high temperatures

SummaryTemperature effects on photosynthesis, transpiration and stomatal resistance were studied in two greenhouse-grown tomato cvs under temperature regimes with maxima of 25° and 35°C. The cvs were Roma VF, which has low fruit set under high temperatures, and Saladette, with high fruit set under such conditions. Transpiration at noon under a high temperature after 48 h acclimatigation was 400% higher than under a moderate temperature, Saladette transpiring slightly less than Roma VF. Stomatal resistance reached a minimum at noon, in accordance with transpiration rate. Leaf water potential (ΨL) reached minima of –1.01 and –0.72 MPa at noon under high and moderate temperatures, respectively. There was no significant difference in Ψ between the cvs. Photosynthesis reached a maximum at 10.00 a.m., with no difference between the cvs. The physiological responses of the two cvs are discussed in relation to fruit set.

Grapevine Irrigation with Saline Water: Effect of Rootstocks on Quality and Yield of Cabernet Sauvignon

ABSTRACT The effects of three irrigation salinity levels (1.8, 3.3, and 4.8 dS/m) on ion accumulation and relative turgidity of Cabernet Sauvignon (Vitis vinifea) grapes on ‘Rugerri’ and ‘Salt Creek’ rootstocks were studied in order to introduce more saline water in the Negev Desert of Israel. Leaf samples were taken four times during the summer of 1997 and analyzed for total diffusible ions, which included sodium (Na), calcium (Ca), potassium (K), and magnesium (Mg), and for soluble ions, which included zinc (Zn) and manganese (Mn). Quality and quantity of yield were also measured. The lowest relative turgidity, 0.8, was measured at ECi (electrical conductivity of irrigation water) 4.8 dS/m, which decreased with time to 0.75 for all treatments. The Na/K ratio indicated relative sodium accumulation. It increased fast with time from about 0.1 to 1.4 under high salinity and more slowly, from 0.1 to 0.5, under the low-salinity treatment. Average yield of fresh berries under all treatments (except one) ranged between 8.0 and 8.5 kg/vine under the respective saline and fresh-water irrigation. This difference was not significant, but in view of the first-year experiment this result should be regarded as provisional. The juice quality criteria, as determined by the production of total soluble solids (TSS) pH2, improved from 321 to 288, indicating low acidity under the saline treatment and higher acidity under the non-saline treatment. The ratio of TSS/acidity, which changed slightly from 34 to 32, also indicated a moderate reduction in acidity under saline conditions, especially under the ‘Ruggeri’ rootstock. Thus, it was concluded that (a) by the use of saline water the quality of the berries may be improved, (b) ‘Ruggeri’ rootstock was less affected than ‘Salt Creek’ by salinity in both quantity and quality of yield, and (c) relative sodium (Na) content in the lamina and the petiole increased with time during the growth period while relative turgidity declined, indicating a possible accumulation of toxic ions over time.

Effects of irrigation according to water deficit in two different soil layers, on the yield and growth of apple trees

SummaryIn a 5-year experiment in the Hula Valley six irrigation treatments were given to replenish the soil water of the 0-60 or 0-120 cm layer whenever a predetermined level of available water was reached. The highest yields and greatest fruit sizes were obtained from a treatment involving irrigation to 60 cm from 10th June to 10th August whenever the 0-60 cm layer reached 40% available water, and during the rest of the season when it reached wilting point. During these two periods the moisture content of the 60-120 cm layer was kept above 80% and 60% respectively. During the final year the yield obtained from this treatment (124 tons per ha,-with an average fruit diameter of 6.22 cm) was about 30% higher than in a treatment copying commercial practice in the area. Analysis of water use efficiency showed that this former treatment produced comparatively more fruit as well as more roots and shoots per mm of water consumed. It was suggested that the smaller fruit size obtained in other treatments was a res...

Effect of drip irrigation on the yield and quality of Golden Delicious and Jonathan apples

SummarySix drip irrigation treatments were applied to a six-year-old apple orchard during 1977-1980. Four treatments received the same amount of water (1.0 class A pan evaporation coefficient from June to harvest), but differed with respect to the volume and the surface area of irrigated soil by using emitters with different discharge rates, different numbers of laterals per tree row and continuous v. pulse irrigation. Yields, growth, fruit size and crop load were not significantly affected by these irrigation treatments. Two additional treatments received less water (0.75 class A pan evaporation from June to harvest), one continuously and the other by pulse irrigation. Yields, growth and fruit size were decreased and crop load was increased compared to the other four treatments. Pulse irrigation of 30 min on and off reduced crop load under irrigation with the 0.75 pan coefficient but not with the 1.0 pan coefficient. The pulse irrigation effect was more pronounced in cv Golden Delicious, which had higher...