Maximum Daily Trunk Shrinkage Research Articles

Can almond trees directly dictate their irrigation needs?

Many of California's fruit and nut growers have already embraced more efficient irrigation systems (drip and microsprinkler) and adopted scientific irrigation-scheduling methods that closely match net applied water to evapotranspiration (ETc). Further improvements in irrigation efficiency may be possible by using regulated deficit irrigation (RDI) to purposely stress trees at specific times of the season. Tree-based RDI triggers for irrigation scheduling, such as stem water potential (SWP) and maximum daily trunk shrinkage (MDS), as opposed to soil and atmospheric measurements, have the major advantage of being directly linked to crop productivity. The current state of the art in plant-based scheduling is SWP and MDS, but adoption is hampered by the lack of field studies validating its effectiveness. We conducted an experiment in a commercial almond orchard to evaluate the suitability of MDS measurements as indicators for RDI management. Small, electronic sensors affixed to the tree trunks continuously recorded diameters from which MDS values were gleaned and used to schedule two RDI treatments. We found that with the less severe RDI regime, less water was applied relative to the cooperator's nearly fully irrigated trees with no significant reduction in kernel size or other important almond parameters. In fact, the RDI regimes accelerated hull-split, decreased kernel water content and increased the nut-kernel percentage at harvest — all desirable almond results. We have demonstrated, for the first time in California, that RDI can be successfully scheduled based entirely on continuously recorded, tree-based electronic data. We believe that MDS measurements have some operational advantages over SWP, including lower labor costs and the ability to be directly incorporated into remotely operated, electronic controllers.

Sensitivity and Variability of Maximum Trunk Shrinkage, Midday Stem Water Potential, and Transpiration Rate in Response to Withholding Irrigation from Field-grown Apple Trees

The sensitivity of water stress indicators to changing moisture availability, and their variability, determine the number of measurements that should be taken in order to represent properly plant water status in a certain orchard. In the present study we examined the sensitivity and variability of maximum daily trunk shrinkage, midday stem water potential, and daily transpiration rate in their responses to withholding irrigation from field-grown drip-irrigated `Golden delicious' apple trees in a commercial orchard. Irrigation was withheld from the stressed trees for 17 days starting in mid-July, and the control trees were irrigated daily at 100% of the “Class A” pan evaporation rate. The courses of daily transpiration rate, maximum trunk shrinkage, and midday stem water potential before and 10 days after the drying period were similar in the control and the stressed trees. Highly significant differences between the stressed and the control trees in their midday stem water potentials were apparent from the early stages of the stress period. Daily transpiration rate and maximum daily shrinkage were more variable than midday stem water potential, and differences between treatments became significant only after measurements were expressed relative to the initial values before irrigation was witheld. Differences between treatments (as percentages of the values obtained for the control trees) increased after irrigation stopped where these differences were greatest for maximum daily shrinkage, which reached 90%; moderate for stem water potential (60%); and least for daily transpiration rate, for which the differences remained below 20%. Our data show that the choice of a certain water stress indicator should be based on both the sensitivity to changing moisture availability and the degree of variability. Possible reasons for the different sensitivity to moisture availability and the different variability between the water stress indicators under study are discussed.

Irrigation scheduling protocols using continuously recorded trunk diameter measurements

Theoretical and experimental aspects of developing irrigation scheduling strategies using continuous measurements of trunk diameter are presented. The behavior of parameters derived from trunk diameter measurements (TDM), including maximum daily trunk shrinkage (MDS), maximum daily trunk diameter (MXTD), and minimum daily trunk diameter (MNTD) is evaluated for both rapidly growing peach [Prunus persica (L.) Batsch, cv. September Snow] and mature almond [Prunus dulcis (Mill.) Webb cv. Price] trees subjected to mild deficit irrigation. Stem water potential (SWP) and MDS were highly correlated in the mature almond trees but a poor relationship was found in the rapidly growing peach trees. Conversely, daily changes in MXTD and MNTD correlated well with SWP in the fast growing trees. While there was relatively high variability ("noise") in the MDS measurements (CV 15.8%), the greater changes in the magnitude of the MDS ("signal") resulted in a significantly higher signal:noise ratio than found with the SWP measurements. In addition to soil water and trunk growth rate, MDS patterns were influenced by irrigation frequency and evaporative demand. Based on the experimental results, protocols for utilizing the trunk diameter-derived indicators for scheduling irrigations are presented for three cases: (1) mature trees under low frequency irrigation, (2) mature trees under high frequency irrigation, and (3) young trees under high frequency irrigation. The scheduling protocols provide guidelines that address both under- and over-irrigation and are predicated on the sensitivity of TDM to very mild plant water deficits. The necessity for and approaches to developing reference (baseline) and threshold values derived from TDM are emphasized. We conclude that protocols using TDM for precise irrigation scheduling hold promise as an additional tool for progressive growers who want to link irrigation management to an automated, electronic, plant-based stress indicator.

Assessment of peach tree responses to irrigation water ficits by continuous monitoring of trunk diameter changes

SummaryContinuous monitoring of trunk diameter and of sap flow were investigated to evaluate and characterize tree responses to irrigation water deficits in peach trees (Prunus persica (L.) Batsch ‘O’ Henry’). A gradual reduction of irrigation during a three-week period followed by a 17 d recovery was applied to field-grown (SF) and lysimeter-grown (SL) trees. Trunk-diameter change (TDC) measurements and maximum daily trunk shrinkage (MDS) were compared with predawn leaf water potential (PLWP) and midday stem water potential (SWP). TDC was also compared with sap flow calibrated in a weighing lysimeter. The experimental calibration of sap flow (r = 0.95) in a lysimeter showed a 45% underestimation of tree transpiration with a coefficient of 0.55, similar to values found in other tree species. The reductions of water supply were reflected clearly by MDS which showed differences among treatments after only 4 d of 75% ET application. MDS was closely related to PLWP and to midday SWP in both deficit irrigation treatments, and some hysteresis between TDC and SWP was detected. There was a strong relationship between the relative sap flow (sap flow of stress treatment relative to control values) and the relative maximum daily shrinkage. Both parameters were sensitive to water stress, as their values declined by 60% with the development of stress. The relationship between sap flow and TDC shows a hysteresis loop whose shape depended on the stress level. As stress developed, the divergence between MinTD (time of day at which minimum TD was reached) and MaxET (time of day when maximum lysimeter evapotranspiration, ET, was attained) increased. It appears that automated trunk diameter measurements provide a precise irrigation management method for the improvement of irrigation scheduling of peach trees.

Sensitivity of Continuous and Discrete Plant and Soil Water Status Monitoring in Peach Trees Subjected to Deficit Irrigation

To characterize tree responses to water deficits in shallow and deep rooted conditions, parameters developed using daily oscillations from continuously measured soil water content and trunk diameter were compared with traditional discrete monitoring of soil and plant water status in lysimeter and field-grown peach trees [Prunus persica (L.) Batsch `O'Henry']. Evaluation occurred during the imposition of deficit irrigation for 21 days followed by full irrigation for 17 days. The maximum daily available soil water content fluctuations (MXAWCF) taken at any of the four monitored root zone depths responded most rapidly to the deficit irrigation. The depth of the MXAWCF increased with time during the deficit irrigation. Differences relative to a fully irrigated control were greater in the lysimeter than the field-grown trees. Minimum daily trunk diameter (MNTD) and maximum daily trunk shrinkage (MDS) responded sooner than midday stem water potential (stem Ψ), predawn or midday leaf water potential (predawn leaf Ψ and leaf Ψ), or photosynthesis (A). Parameters based on trunk diameter monitoring, including maximum daily trunk diameter (MXTD), correlated well with established physiological parameters of tree water status. Statistical analysis of the differences in the measured parameters relative to fully irrigated trees during the first 10 days of deficit irrigation ranked the sensitivity of the parameters in the lysimeter as MXAWCF > MNTD > MDS > MXTD > stem Ψ = A = predawn leaf Ψ = leaf Ψ. Equivalent analysis with the field-grown trees ranked the sensitivity of the parameters as MXAWCF > MNTD > MDS > stem Ψ = leaf Ψ = MXTD = predawn leaf Ψ > A. Following a return to full irrigation in the lysimeter, MDS and all the discrete measurements except A quickly returned to predeficit irrigation levels. Tree recovery in the field-grown trees was slower and incomplete due to inadequate filling of the root zone. Fruit size was significantly reduced in the lysimeter while being minimally affected in the field-grown trees. Parameters only available from continuous monitoring hold promise for improving the precision of irrigation decision-making over the use of discrete measurements.