Relation between Apple Root Distribution and Soil. Water Extraction in Different Irrigation Regimes. I. LEVIN, B. BRA VDO, and R. ASSAF. The distribution of ...
7 Relation between Apple Root Distribution and Soil Water Extraction in Different Irrigation Regimes I. LEVIN, B. BRA VDO, and R. ASSAF
The distribution of roots in soil is a dynamic process controlled by factors such as aeration, moisture content and availability of nutrients (KRAMER, 1969). Apple trees, which are characterized by a large crown and are expected to support heavy crops, require an adequate, well-distributed root system, in order to supply water and nutrients for growth and yields (GARDNER et at., 1952). The main factor determining distributing of apple-tree roots under orchard conditions is the relation between soil water-content and aeration. The common practice of nontillage prevents the development of high temperatures and root damage (KRAMER, 1969). In pears (French rootstock) grown in heavy soil, 35% of the roots in the 0-120 cm profile were concentrated in the 0-30 cm layer, while only 11% were found in the 90-120 layers (ALDRICH, 1935). In oaks and pines in heavy soils, 90% of rootlets (smaller than 2.5 mm in diameter) were concentrated in the upper 12.5 cm layer (COILE, 1937). A similar situation prevailed in the same species grown in light soils due probably to frequent wetting of the upper layer by rain. Excess of soil water was found to cause lack of aeration and reduce root development (KRAMER, 1969). When moisture content was 81% of field capacity, the number of rootlets was 10-11 times less, in comparison to optimal moisture content at 55-60% of field capacity (EREMEEV, 1960). Low soil water content caused apple roots to have one-sixteenth of the number found in the controls, which received a "normal" irrigation regime (GORIN, 1963). Unirrigated apple trees developed half the amount of roots that irrigated trees did (GOODE and HYRYCZ, 1964). The effect on apple root distribution of controlled water regimes at different depths has not yet to our knowledge been investigated. Herewith are results of the effect of five irrigation treatments applied during the past four years on root distribution and water uptake from different depths of the 0 -180 cm profile.
Materials and Methods Five sprinkle treatments were applied to an apple orchard-Grand variety (Calville de St. Sauveur), on Malus rootstock (seedling) planted in 1958 4.0 X 5.5 m apart at Kibbutz Hulata in the southern Hula Valley in Israel. The experimental site is located 70 meters above sea level. Average annual precipitation (limited to the winter) is 400 mm. Average daily temperature is 24 0 C in summer and 11.5 0 C in winter. Summer season is from May to September. The soil is brown clay grumusol, uniform throughout the 200 cm profile with 48% clay and 39% silt. The groundwater table was below 4 m throughout the summer. The field capacity (determined gravimetrically) (Pw) was 27%
A. Hadas et al. (eds.), Physical Aspects of Soil Water and Salts in Ecosystems © Springer-Verlag Berlin · Heidelberg 1973
352
1. LEVIN, B.
BRAVDO,
and R.AssAF:
in the 0-30 cm layer and 25% in the rest of the profile, wilting point 17% (Pw), bulk density 1.42 and pH 7.6. Each treatment was applied to a plot of four trees with two border trees on each side, replicated six times in randomized block design. Na'an sprinklers No. 213 with 2.2 mm nozzles supplying 250 lIhr were placed 5.5 X 6 m apart. This spacing was adapted after a preliminary test in which cans were used to collect the water at different distances from the sprinklers, when it was found that the variation coefficient of water collected was 33% in the open field, and 28.4% in the orchard. Access tubes 2.4 m long were driven into the soil at 1.75 m from each tree for determination of soil water content by the neutron scattering method (Troxler U.S.A.). This was followed in five replicates for each treatment, while the sixth served as a guide plot, and contained 25 tubes located 1 X 1 m apart inside the square created by the experimental trees. This plot provided more detailed soil moisture readings. Soil water was determined before and after each irrigation, and, in most cases, between irrigations also. Evapotranspiration was determined by extrapolating the lines connecting soil moisture values. The treatments consisted of replenishing the moisture deficit to field capacity in the 0-60 cm or 0-120 cm soil layer profile after moisture content had reached a predetermined level, selected according to soil moisture determinations carried out during the two years prior to the beginning of the experiment. The orchard was sod, cultivated prior to and during the experimental period as is common practive in local commercial orchards. Sixty kg/dunam! (NH4hS04 were applied yearly and 80 kg/dunam KCI biyearly. The irrigation treatment plan is given in Table 1. Table 1. Plan oftreatment Treatment
Available soil water before irrigation (%) 0-60cm
W.P. + 10 daysa 20 T3 Medium T4 Combined like T6 from 10. VI -10. VIII and 0% of 0-60 cm, 50% of 60-120 cm for the rest of the season. TSb Commercial 50% of 0-120 cm profile 40 T6 Wet
Tl Dry
60-120cm
40 60
80
a 10 days after wilting point (W.P. was reached). b Common commercial irrigation practice in the Hula Valley.
Annual growth was measured for fifty shoots on each of the twenty-four trees of each treatment at the end of the season. In November, 1970, a typical tree was selected from every treatment for the specific purpose of root survey. A ditch was dug parallel to the rows and at 1 m distance from the trunks to a 2.50 m depth. Roots were exposed by rinsing the walls of the ditch with water. Mapping of roots was done in successive 20 X 20 cm squares along a line 1.4 meters from each side of the trunks and to 1.8 meter depth. Each root was marked on the map
1 dun am = 1000 m2
353
Relation between Apple Root Distribution and Soil Water Extraction
according to size. The sizes were then divided into five ranges: the smallest measuring 1 mm or less, and the biggest 10 mm or more.
Results Table 2 shows data related to yield, fruit size and growth under various irrigation treatments in 1970, The dry treatment (T 1) differed considerably from the rest of the treatments in all respects. Table 2. Irrigations regimes, yields and shoot growth in 1970 Treatment
Total no. of irrigations
4 Ttdry T3medium 10 T 4 combined 12 Ts commercial 11 T 6 wet 20
Irrigations to 120 em
4 0 2 11 0
Water applied (mm)
Yield kg/dunam
660 835 890 1,065 1,205
7,500 9,940 11,400 9,570 10,170 SE472
Large fruits (%)a
13 43 64 37 36
Young Kg fruits shoot permm average water length (cm) 7.8 16.1 19.7 17.9 19.3 SEO.268
11.36 11.30 12.80 8.90 8.44
a Diameter of 6.5 em and over.
Soil 10,., (em)
T1
T3
0- 30 30- 60 60- 90
T4
90- 120 120 - 150 150- 180
0- 30 30- 60 60- 90 90- 120 120-150 ISO-I80
Fig. 1. Relative evapotranspiration from different soil layers ('Yo)
Treatments 3, 4, 5, 6 differed mainly in the percentage of large fruits, while growth and yields differed less between treatments. The combined treatment (T 4) excelled in yield, growth, fruit size and yield produced per unit of water consumption. Fig. 1 shows the relative water extraction from the different layers in the five treatments. Most was extracted from the two upper layers (0-30 and 30-60 cm) in all treatments. In treatment 1, however, 45% of the water was extracted from layers deeper than 60 cm, as compared with 25% in treatment 6.
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