Test PB Collection: FTE

We have several year's experience with a dormant season procedure for sampling shoots. There are still many details to work out, but it appears to show promise for some nutrients.

Phosphorus is an important nutrient in all plants as it is required for membranes, energy molecules and nucleic acids. However, it is seldom deficient in stone fruit trees in California.

Sulfur deficiency has never been documented in California stone fruit orchards. This is probably because S is found in many fertilizers and is abundant in most soils. In addition, it is found in the atmosphere and is carried into the soil by rain.

Copper deficiency is rare in California stone fruit orchards but has been observed in plums growing on Nemaguard rootstock. Symptoms include shoot dieback and formation of small, chlorotic and malformed young leaves. Rough bark accompanied by gumming also occurs.

Both these nutrients are needed in very small amounts in fruit trees. Deficiencies have never been documented in the field, so leaf threshold levels have not been established. When we have analyzed leaves for Mo, values have generally been between 0.04 and 0.30 ppm.

Chlorine is needed in very small amounts in fruit trees, but is seldom deficient. The more serious problem with this element is when it is in excess, leading to salt toxicity. Peach, plum and nectarine are particularly sensitive to this disorder. Leaf levels need to be kept below 0.

Having peach trees in the lysimeter for nearly 20 years has allowed us to determine precise crop coefficients for orchards under different conditions. The graph on the right and chart below show average crop coefficients for mature peach trees.

These are yearly crop coefficient plots for each year of the two peach plantings in the lysimeter. Both varieties were planted at a 6'x16' spacing and trained to a Kearney "V" system (Kearney Perpendicular "V" Training System - 1994).

The lysimeter at Kearney has been used to measure peach water use. It is essentially a large planter box on top of a sensitive truck scale. It can accurately measure the hourly loss of water by soil evaportation and tree transpiration (evapotranspiration or ETc).

After conducting several experiments, we have developed deficit irrigation strategies that can save substantial amounts of water.