Update 2012: Water Status & Demand

This project focuses on the interplay between water and nutrient management, and, among others, the question of whether or not the nutrient status of the plant can influence plant water demand, or the water status of the plant can influence nutrient demand.

Specific Objectives for 2011

1. Document the amount and timing of water applied to each study site
2. Monitor plant water potential at each of the fertilizer/nutrient study sites to determine whether irrigation and fertilization levels independently influence tree nutrient status
3. In the southern San Joaquin Valley site, use soil moisture, meteorological, and satellite-based remote sensing methods to monitor non-stressed almond evapotranspiration (ET) under both drip and microsprinkler irrigation. Assess the impact, if any, of fertility on almond ET through replicated sites in this one orchard.

Relationship of SWP to Leaf Gas Exchange & Yield

Both water and nutrient status of trees at four orchards across the state are being monitored with pressure chamber and leaf sampling methods, respectively. In these orchards, irrigation is managed by growers to address a variety of factors such as minimizing hull-rot or ensuring a dry ground for harvest, any of which may affect tree water and nutrient status as well as yield. 

There was no clear relation of current year yield to current year SWP, but an indication of a positive relation of current year yield to previous year SWP (Table 1 below). Across sites and years, there is evidence that irrigation management and SWP have the strongest influence on yield as a 1-year carryover effect, rather than a current season effect.  Stomatal opening and hence leaf transpiration appears to be primarily influenced by SWP (Figure 1 top panel)  and only secondarily influenced by leaf exposure, whereas for leaf photosynthesis the opposite is the case (Fig. 1 bottom panel).

Estimating Crop Water Use (ET) Using Crop Coefficients (Kc)

At one site in the southern San Joaquin Valley, a variety of fertilizer treatments are being applied and canopy evapotranspiration (ET) is being measured.

The data so far do not indicate a strong influence of nutrient status on ET, but do indicate that almond trees have a higher ET than previously thought (Fig. 2). These results should lead to more accurate estimates of the almond crop coefficients used to estimate irrigation needs.


For more information see the presentations and publications under Outreach.