Tree Fruit Leader, Vol. 3(1) Jan. 1994

Getting Trees to Grow

by Tim Watson, Horticulturist BCMAFF, Oliver

Good growth is essential if high density plantings are to succeed. Many growers rate lack of growth in new plantings as their number one concern.

BCMAFF horticulturists, with funding from the OVTFA, initiated the 1993 replant project to study and assess factors affecting growth of the 1993 fruit tree plantings and to determine optimum management techniques. During the year project leaders had an opportunity to see the new plantings and discuss management practices with the orchardists.

Background

Detailed information was obtained on 1993 plantings established in 171 orchards throughout the Okanagan and Similkameen Valleys. Planning, preparation and planting procedures were documented. Highlights of the survey are given in Figure 1 and in point form below.

• 18 percent of orchardists had a replant analysis carried out 
• 43 percent did a soil chemical analysis 
• 11 percent fumigated the replant site before planting 
• 64 percent added soil amendments before planting 
• 76 percent of the plantings were trained to spindle 
• there were 10 super spindle plantings 
• Gala, Fuji, Braeburn, Spartan, and Sunrise were the main new varieties planted 
• 60 percent of the plantings were on M.9 rootstock 
• 79 percent of the orchardists rated tree condition as excellent or good when the trees were received 
• the range of planting dates varied, with some too late (early May) 
• use of phosphate fertilizer at planting is common 
• there were some unacceptable delays in management practices -- for example tying trees to the support 
• 52 percent of the orchardists fertigated new plantings by flooding or irrigation system injection

Growth Measurements

Tree development was determined by monitoring tree caliper and extension growth. Tree calipers varied widely. The area of trunk cross section (TCSA) was calculated from caliper measurements. Some area measurements were unacceptably small (a TCSA of less than 80 mm² is likely inadequate). These trees may never achieve their full production potential, or production may be delayed.

A second caliper measurement made at the end of the growing season also showed that there had been a wide range of increases in growth in the first growing season. The increases in TCSA ranged from about 30 mm² to 300 mm². This tenfold difference is much greater than desirable and indicates a lack of uniformity in the development of new plantings.

Extension growth was measured in a number of orchards in late August and September.

Total extension growth averaged from as low as 150 cm to more than 670 cm per tree in different replant blocks.

Taking caliper and extension growth into consideration, about 33 percent of the plantings had optimum growth in the first year, 46 percent were adequate and 21 percent of the trees did not achieve adequate extension growth.

Soil Solution Measurements

Soil solution measurements of nitrate, conductivity, and pH were taken in 52 orchards. The first two measures were found to be valuable for monitoring fertility levels during the season and for identifying levels that were so high as to possibly injure trees. Soil solution pH does not appear to be a useful measurement for monitoring tree development.

Figure 4 illustrates the average soil solution nitrate levels for the season in the 52 blocks measured. The variation in levels is significant.

With the increase in fertigation use, careful monitoring and management of soil nutrient levels will be a critical factor in the success of new plantings.

This year's results do not indicate a high correlation between the averaged values for soil solution and growth measurements. This relationship should be monitored in the subsequent development of these plantings for growth and yield.

Soil Analysis

Soil samples were taken in most new plantings. Soil pH values were generally satisfactory, however in a significant number of drip-irrigated plantings, low pH levels were found under the dripper area. This is surprising considering the short period of fertilizer application. Boron levels were low in an exceptionally high number of soils. Both the pH changes and low boron levels require attention, especially in new plantings.

Leaf Analysis

Leaf analyses were also carried out in most 1993 replant blocks. In most instances, levels were optimal for the major nutrients (nitrogen, phosphorous, and potassium). Foliar levels of the minor elements (boron, magnesium, and zinc) were generally low. An increase in the use of foliar applications of minor nutrients is desirable for new plantings.

Moisture Measurements

Soil moisture was monitored in 18 orchards over five to seven weeks. Measurements were taken with an instrument that uses reflectance analysis of moisture in the soil (IRAMS).

Figure 5 shows the results obtained from one replant block. Soil moisture is shown for two depths, 0-40 cm and 40-80 cm. Less than 10 percent moisture in the 0-40 cm zone is low and could affect tree growth.

Reflective measurements gave an accurate assessment of soil moisture, however it is not easy to make use of this information in irrigation management practices. This method of soil moisture evaluation therefore has limited use in tree fruit plantings.

Summary of Project

• Some new plantings progressed very well in 1993.
• The overall performance of new plantings could improve if replant analysis, soil testing, fumigation, and fertigation were used more widely.
• The overall performance of many plantings could improve if more attention were paid to weed control and irrigation scheduling.
• Levels of the major nutrients were generally satisfactory. The levels of minor nutrients were low in a surprising number of plantings and greater use of foliar applications is desirable.
• Soil solution monitoring appears to be valuable in monitoring the status of some nutrients in the soil. Nitrate levels varied widely in new plantings.
• Soil moisture percentages were adequate in many new plantings. Some appeared over-watered and some had moisture levels low enough to affect tree development adversely.
• Tree growth was considered optimum in about 33 percent, inadequate in 21 percent, and adequate with room for improvement in the remaining 46 percent of measured plantings. Growth may have been excessive in a small number of blocks.

A detailed project report is being prepared.

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