Scientific Team

Management of Soil and Water in Date Palm Orchards of Coachella Valley, California

Aref A. Abdul-Baki and Sam Aslan

Plant Physiologist, Sustainable Agricultural Systems Laboratory, Beltsville Agricultural Research ,Center, U.S. Department of Agriculture, Beltsville, Maryland 20705, USA

Soil Conservationist, Natural Resources Conservation Service. U.S. Department of Agriculture, Indio, California, USA

Abstract

The Date palm (Pheonix dactyliphera) in the U.S. occupies an area of approximately 2428 hectares of land in Coachella Valley, southeast California, and 364 hectares in Bard, near Yuma, Arizona.  The date palm tree was introduced into North America in the early part of the 20^th Century.  During the early years, over 100 varieties were evaluated in Texas, Arizona, and California for adaptability and performance.  Major varieties include Deglet Noor, Mejhool, Khadrawi and Zahidi.  Annual rainfall in the date production area averages about 75 mm.  Consequently, all orchards depend on irrigation from the Colorado River.  The two commonly used methods for water delivery are basin irrigation and drip irrigation.  The former is used for bearing-age orchards; the latter for date nurseries and newly planted orchards up to five years.  Water management is governed by many important factors including orchard age, availability of water and soil properties which include texture, compaction, stratification, low fertility and high salinity.  Soil management operations are designed to overcome major problems that limit tree growth and yield.  These include slip plowing prior to planting the orchard, reducing the use of heavy machinery in field operations, maintaining adequate levels of soil fertility, controlling weeds, and leaching excessive salts.  All these operations impact tree vigor, yield and fruit quality. 

Introduction

The date palm is an old native of the arid Middle East and North Africa.  It has been grown there for thousands of years providing food, feed, fiber and shelter for the natives.  Date palms were introduced to the North America during the early 20th century through the efforts of the United States Department of Agriculture (USDA), the University of California, and private citizens.  Over one hundred varieties of date palm offshoots were imported to the U.S.  They were evaluated for performance in the southwestern states of Texas, Arizona and California.  The arid southern interior low desert of California and Arizona (Coachella Valley and Bard) proved to be most suitable for tree growth.  Some plantings in the Phoenix area thrived more than 60 years.  At present, the 6,000 acres (2,428 hectares) of the Coachella Valley date orchards represent 87% of the total date palm acreage in the U.S.  The remaining 900 acres (364 hectares) are located in Bard near Yuma, Arizona.  Together these 6,900 acres (2,792 hectares) compromise the date producing area of North America.  Major varieties include Deglet Noor, Mejhool, Khadrawi and Zahidi.

Climate

 The Coachella Valley – the main date palm growing area in the U.S., has an area of 75,000 acres (30,000 hectares) and extends from the city of Palm Springs in the north to the Salton Sea in the south.  Climate is a major determinant in successful date production.  A long, hot and arid growing season is required for date palm growth and for fruit development and maturation.  Early maturing varieties, such as Deglet Noor and Mejhool, require about 6500 degree-days of heat units from flowering to fruit ripening (Cook, 1956).  Late varieties, such as Helali and Kasab, require over 7,000 degree-days.  Table 1 shows the average monthly maximum air temperatures during the growing season for the Coachella Valley (Indio, CA) and Bard, AZ,  and compares them with two major date production locations – Basra, Iraq, and Touggourt, Algeria.  Maximum air temperatures among all these production locations compare favorably.

Rain and high humidity adversely affect date production.  Rain at the last stage of pollen maturation reduces viability and storability.  At the Khalal stage, rain induces long and deep cracks in the fruit.  If the fruits absorb moisture during the Rutab stage, they turn sticky and become subject to fermentation and souring.  Rain and high humidity are the main limitations to extending date growing to tropical areas of the U.S., such as Florida, although the degree-day requirements are met.

The sensitivity of the date fruit to damage by rain is illustrated in Table 2.  Just a few days of rain, especially between August and October, can inflict serious crop losses.  In general, damaging rains in Coachella Valley occur about once every ten to fifteen years.  Likewise, high relative humidity causes severe damage to fruits.  The relative humidity in Coachella Valley is stable all year round and ranges between 33 and 41 percent.

Soil Management

Soil management is a critical and costly operation in the arid, desert areas of date production.  It begins as early as planning the orchard and continues throughout its life.  Successful management of the Coachella Valley soils has to deal with several major soil problems that limit productivity such as soil compaction, stratification, low fertility, high salinity, competition by weeds, and severe soil erosion by wind.  These problems are likely to be unique to the Coachella Valley.  Because of their importance, I will describe the soil types and present a brief account of the most common management practices to overcome these problems.

Soil type

 In 1980, soils of the Coachella Valley date orchards were surveyed and mapped by the USDA Soil Conservation Service (Knecht et al., 1980).  The survey classified the soils where date palms grow into five major series.  The name and water holding capacity of each series appear in Table 3.  Best yields and fruit quality are produced on Gilman and Indio soils which have high water holding capacity and moderate permeability.  Gilman and Indio types are the most common soils in Coachella Valley date orchards.

Soil compaction

 Soil compaction is man made.  It is induced by heavy farm machinery and is usually limited to the uppermost 12 to 18 inches (30-45 cm) of the soil profile.  Man-made soil compaction may be reduced or even totally eliminated by eliminating field operations that use heavy machinery.

Soil Stratification

 Soil stratification in Coachella Valley originated during the Valley’s soil formation.  It was caused by water and wind forces that eroded soil from San Jacinto Mountain in the east and Indio hills in the west mountain ranges and deposited it in the Valley.  Stratification can be observed at all soil depths.  Both man-made compaction and stratification result in poor permeation of water through the soil profile into deeper zones.  Lack of adequate permeation leaves the lower zones dry such that the date roots do not grow deep.  Rather, they remain restricted to the shallow zones of the soil profile.  This situation further reduces the number of roots per tree (Table 4).  Together with the shallow root system and fewer roots, the trees become subject to damage by strong winds. It is not uncommon to have 60 to 70 mile per-hour (90-110 km) wind in the Valley.  Fallen or bent trees, especially at bearing age, are evident indicators of a shallow root system inflicted by soil compaction (Fig. 1).  The impact of soil compaction (expressed as pounds per square inch and mega Pascals) on the number of roots per tree, and the frequency of compaction in date orchards, appear in Table 4.

Stratified layers that inhibit water permeation can be of varying thicknesses.  Breaking up the strata and mixing the soil to a depth of several feet in small orchards can be achieved with a backhoe.  Larger operations can best be accomplished by using a slip plow.  The plow is about 20 inches (50 cm) wide and capable of shattering soil layers to a width of 5 feet (1.5 m) on each side and to a depth of 6 feet (1.8 m) (Fig. 2).  Slip plowing costs about $250 per acre.  The slip-plowed area usually gets recompacted after several years such that this operation may have to be repeated every three to five years.  Slip-plowing is best done before planting the orchard.  If done at fruit-bearing age it can cause significant damage to the roots of the date trees.

Soil compaction and stratification interfere with the uniform lateral and vertical movements of water and fertilizers through the soil profile and ultimately with root growth and distribution in the soil.  When permeation is severely reduced, water stays on the surface for five to twelve days.  The basin becomes a swamp and provides an ideal breeding ground for mosquitoes which, in turn, become a health hazard.

Poorly drained basins accumulate salt which is normally leached down by excessive water and improved permeation.  Furthermore, poorly drained soils do not allow adequate gas exchange.  Root growth becomes restricted due to lack of oxygen and buildup of carbon dioxide.  Under these conditions, root growth slows down or even stops and uptake of nutrients and water are greatly reduced.  In hot weather, the trees look wilted, even in the presence of soil moisture, due to poor water uptake by the roots.

The impacts of soil compaction and stratification are not limited to date palm root growth. Rather, they also adversely affect soil microbial activity including nitrogen fixing bacteria and mycorrhizae. 

Finally, when irrigation water remains on the surface of the basin for several days, water use efficiency reaches its lowest level especially in the hot summer months during which evaporation of water from the soil surface is high

Improving Soil Fertilit

 Soils of Coachella Valley are typical of desert soils.  They are sandy with low water holding capacity (Table 3).  Consequently, leaching of nutrients from well-drained fields is very high, especially when using flood-basin irrigation.  Because of its high solubility and high demand by the date palm, nitrogen is the most needed nutrient.  It is usually supplied as a commercial fertilizer in one application per year.  Furr (1951) reported that about 5 to 6 pounds (2.3-3.0 kg) of nitrogen per year are needed by a full-bearing Deglet Noor tree.  Animal manures are often used to supplement commercial fertilizers and add organic matter to the soil.  However, the high temperatures during most of the year “burn” the organic matter and reduce its concentration in the soil to less than one percent.  Use of cover crops and composted shredded leaves can improve organic matter content and nutrient recycling.  On the other hand, cover crops consume additional water thus raising production cost, and may interfere with field operations such as pruning, pollinating, thinning and harvesting.  They may also serve as hosts to pests.  Thus, the use of cover crops should be evaluated carefully taking into consideration additional cost and availability of water.     

Competition by Weeds

Weeds compete with the date palm trees for water and nutrients.  Most date growers do a lot of cultivation to control weeds (Fig. 3), while others use cover crops in a no-till system (Fig. 4)

Water Management

Water Requirements

The consumptive water used by the mature, full-bearing ‘Khadrawi’ date tree was estimated (Furr and Armstrong, 1956; Pillsbury 1937, 1941) to be 51.1 acre-inches (129 ha-cm) per year (Table 5).  It should be noted that ‘Khadrawi’ trees have a relatively small size compared to other varieties and thus use less water.  The highest average annual use of water occurs within the soil profile between 1 and 5 ft (30-150 cm) depth.  These findings coincide with our findings which showed that the highest root density for both fibrous and feeder roots were located between 2 and 5 ft (24-150 cm) of the soil profile (unpublished data).  An additional 4 to 5 acre-feet (120-150 ha-cm) per year was further estimated to account for direct evaporation of water from the soil surface, use by weeds, irrigation inefficiencies, and leaching.  Hence, the overall water

requirement for the ‘Khadrawi’ full-bearing tree in Coachella Valley is about 9 to 10 acre-ft per acre (270-300 ha-cm/ha) per year.  ‘Mejhool’ trees are larger than ‘Khadrawi’ and may require more water.

Water source and deliver

All agriculture in Coachella Valley depends on water from the Colorado River.  Date orchards are planted in rows allowing 30 feet (9 m) between rows and 30 feet (9 m) between palms within the row.  This standard planting geometry allows planting about 48 palm trees per acre (123 trees/ha).  Permanent basins with 2 feet (24 cm) are established along the tree rows.  Hence, the standard dimensions of the basin are 30 ft (9 m) wide and 300 ft (90 m) long.

Except for date nurseries and newly planted orchards where drip irrigation is commonly used (Fig, 5), the standard irrigation methods for mature trees is border-basin irrigation (Fig. 6).  An average of 5 to 6 in (12-15 cm) of water is applied at 12 to 14-day intervals during the growing season.  Irrigation is reduced about two weeks before harvest.  Deviation from this general rule depends on the variety, age of the trees, and the type of soil in the orchard.

Future Prospects of Date Production in Southeast California

 It is unlikely that the future years will witness any significant increase in date acreage in southeast California for the following reasons

1.       The Coachella Valley, which encompasses the most favorable date production area in southeast California, is limited to 75,000 acres (30,000 ha) of agricultural land.  This acreage is presently farmed with four major crops with 6,000 acres (2,800 ha) in date palm, 12,000 acres (5,600 ha) in table grape vineyards, 8,000 acres (4,370 ha) in citrus, and about 30,000 (12,000 ha) in vegetables.  This leaves only a very small amount of acreage available for agricultural expansion.

2.       The area extending from Palm Springs in the north to Indio in the south is becoming a very popular tourist attraction.  Population growth in the area is so rapid and investments are so attractive that land is no longer justifiable for agricultural enterprise.  Instead, golf courses are annually on the increase.  At present, there are about 140 golf courses occupying an area of 40,000 acres (16,000 ha) bordering Coachella Valley from the north, and comprising a major component to the area’s economic stability.

3.       The whole southeast part of California depends on water from the Colorado River.  With the rapidly growing urban population in the area, there will be a greater demand for drinking and industrial water at the expense of water for agricultural use.

4.       There has been a rapid growth in the population of Coachella Valley itself in the last two decades which resulted in utilization of some farm land for housing developments.  The new housing developments have raised the value of farm land, increased taxes on land and reduced net returns from agriculture.

Conclusion

In spite of several limitations that will certainly reduce agricultural growth and expansion in the Coachella Valley and Bard areas, date palms will probably be grown longer in these areas than any other crop even as land becomes scarcer.  Factors that support this conclusion include the unique suitability of the soils and the climate to date production, the dedication of the Valley’s growers, and the Coachella Valley Conservation District Authorities to protect this unique and nutritious crop.

References

1.Cook, R.E.  1956.  A study of the relationship of heat units to ripening time of dates.  Date Growers’ Institute.  Report 3313-14.

2.Furr, J.R.  1951.  Irrigation and fertilization experiment with Deglet Noor dates.  Date Growers’ Institute.  Report 2817-20.

3.Furr, J.R. and W.W. Armstrong.  1956.  The seasonal use of water by Khadrawi date palm.  Date Grower’s Institute. Report 335-7.

4.Knecht, A.A., C.R. Simonson, and E. Spencer.  1980.  Soil Survey of Riverside County, California, Coachella Valley Area.  USDA Soil Conservation Service and University of California Experiment Station.                      

5.Pillsbury, A.F.  1937.  How much water does a date palm use?  Date Growers’ Institute.  Report 1413-16.

6.Pillsbury, A.F.  1941.  Observations on use of irrigation water in Coachella Valley, California.  University of California Agricultural Research Experiment Station.  Bulletin No. 644.    

FIGURES

Fig. 1      Date palm trees in compacted soil are bent by wind.

Fig. 2      A DC-9 tractor weighing over 50 Mt pulls a slip plow which shatters compacted soil strata to a 1.8 m depth.

  Fig. 3      A well-managed date orchard kept weed-free by cultivation.

Date Palm Head Management Practices

Abdel – Azim M. El - Hammady

Prof. of Pomology, Dean, Institute of Environmental Studies & Research

Ain Shams Univ., Cairo, Egypt

aelhammady@ hotmail.com

Abstract

Management of date palm head is of great importance since it affect quantity and quality of the produced fruits. These practices include the following

1.       Pruning This practice is carried out to prune old leaves with reduced photosynthesis capacity, dry or diseased leaves, thrones on leaf bases, and removal of old, dry leaf bases that were left after pruning.

2.       Pollination This practice is carried out either, manually or mechanically. The preparation of pollen, storage, pollination practice, importance of pollen source and factors affecting pollination efficiency are discussed.

3.       Fruit Thinning This is usually practiced in the high valued cultivars. Different methods of fruit thinning, either, manually or  by using growth regulators, effect of fruit thinning on yield quantity & quality as well as timing of carrying out this practice are discussed.

4.       Spath Positioning The importance timing and different methods of carrying out this practice is discussed.

5.       Spath Covering This is done, either to protect the fruits from unsuitable environmental conditions, or facilitate harvest, or protection from insects or bird damage. The different materials used for each purpose are discussed with the implementation of the benefits that are achieved.

6.       Harvesting Methods Different stages of fruit growth are discussed, along with how to determine the right stage to harvest for different kinds of dates (soft, semi dry or dry types).

عمليات خدمة رأس النخلة

تبر خدمة رأس النخلة من العمليات الزراعية الهامة والمؤثرة في إنتاجية نخيل التمور ومدي جودة الثمار الناتجة حيث تشمل عمليات خدمة رأس النخلة ما يلي 

1.      التقليم والتكريب .

2.      تقنيات التلقيح   .

3.      تقنيات خف الثمار  .