Improving Pomegranate Fertigation and Nitrogen Use Efficiency with Drip Irrigation Systems

Transcription

1 Improving Pomegranate Fertigation and Nitrogen Use Efficiency with Drip Irrigation Systems Project Leaders James E. Ayars, Ph.D., Research Agricultural Engineer, USDA-ARS, SJVASC, 9611 S. Riverbend Ave., Parlier, CA 93648, ph.(559) , FAX (559) , Claude J. Phene, Ph.D. SDI+ Consultant, P.O. Box 314 Clovis, CA , ph (559) , FAX (559) , Project Cooperators Dong Wang, Ph.D., Research Leader and Soil Scientist, USDA-ARS, Water Management Research Unit, (SJVASC), 9611 S. Riverbend Ave. Parlier, CA (559) , Gary S. Banuelos, Ph.D., Plant/soil Scientist, USDA-ARS, Water Management Research Unit, (SJVASC), 9611 S. Riverbend Ave. Parlier, CA (559) FAX (559) , R. Scott Johnson, Ph.D. UC Extension Pomologist, UC KARE Center, 9249 S. Riverbend, Parlier, CA 93648, (559) , Kevin R. Day, Tree Fruit Advisor, UC Cooperative Extension, 4437 S. Laspina St., Ste B, Tulare, CA, 93274, Direct Phone (559) , FAX (559) , Rebecca Tirado-Corbala, Ph.D. Soil Scientist, USDA-ARS, Water Management Research Unit, (SJVASC), 9611 S. Riverbend Ave. Parlier, CA (559) , Suduan Gao, Ph.D., Research Soil Scientist, USDA-ARS-SJVASC, 9611 S. Riverbend Ave. Parlier, CA (559) Supporting Staffs Rick Schoneman Agricultural Engineer, USDA-ARS, coordinated installation and maintenance of the irrigation system and student support. Rebecca C Phene, Staff Research Associate II, UC Davis, coordinated UC orchard maintenance, developed computer software for the lysimeter and the irrigation control systems, developed the lysimeter KARE website and measured various crop variables. Objectives: The overall objective of this project is to optimize water-nitrogen interactions to improve fertilizer N use efficiency (FUE) of young and maturing pomegranate and to minimize leaching losses of nitrogen. Specific objectives are: 1. Determine the real time seasonal nitrogen requirements (N) of DI- and SDI-irrigated maturing pomegranate that improve FUE without yield reduction. 2. Determine the effectiveness of three nitrogen injection rates with DI and SDI on maintaining adequate N levels in maturing pomegranates. 3. Determine the effect of real time seasonal nitrogen injections (N) with DI- and SDIirrigated maturing pomegranate on N leaching losses. 4. Develop fertigation management tools to allow the growers to achieve objective 1 and present these results to interested parties at yearly held field days and seminars. 5. Determine if concentrations of macronutrients (P, K, Ca, Mg) and micronutrients (Zn, Cu, Mn, Fe, B, Se) and eventually healthy bioactive compounds in soil, peel and fruit are influenced by precise irrigation/fertigation management with DI and SDI.

2 Work Description: This project is using a 1.43 ha (3.54 ac) Pomegranate orchard (var. Wonderful) located on the Kearney Agricultural Center that contains a large weighing lysimeter. This lysimeter will be used to automatically manage the hourly irrigation scheduling on the site and determine the crop water use for the 100% SDI treatment, 100% N-sub treatment. The trees in the 50% N and 150% N sub-treatments will be irrigated at 100% of crop water measured by the lysimeter until feedback from the soil matric potential measurements indicate a need for up and/or down adjustments. The lysimeter tree will be irrigated using a SDI system with the same number of emitter per tree as the rest of the orchard. Trees were planted with rows spaced 4.9 m apart and trees in the harvest rows spaced at 3.6 m along the row. There are 2 border rows with trees spaced at 3.6 m apart. These extra trees will be dug up and harvested yearly for total nutrient uptake measurements during the last years of the project. Figure 1 is a schematic of the plot layout (complete randomized block with sub-treatments) showing main irrigation treatments and N-fertility subtreatments. The main irrigation treatments are DI and SDI (50 to 60 cm. depth) systems with dual drip irrigation laterals, each 0.9 m. from the trees. The fertility sub treatments are 3 N treatments (50% of adequate N, adequate N, based on biweekly tissue analysis and 150% of adequate N, all applied by variable injection of AN-20. Potassium (K 2 S) and phosphorus (PO 4 -P) will be supplied by variable injection of P=15 ppm and K=50 ppm to maintain adequate levels. The ph of the irrigation water will be automatically maintained at 6.5+/-0.5. Tree and fruit responses will be determined by trunk and canopy measurements, pruned plant biomass, bimonthly plant tissue analyses and fruit yield and quality. When appropriate, flowers, fruit yields and quality will be measured and statistically analyzed. Analysis of variance (ANOVA) for the Randomized Complete Block Design (RBCD) with sub-samples will be used to determine the treatment significance. Task and sub-tasks to achieve objectives for year #3 1. Determine the real time seasonal nitrogen requirements (N) of DI- and SDI-irrigated maturing pomegranate that improve FUE without yield reduction. Bi-weekly tissue analyses will be used to provide N-uptake rates from three N application levels and will be used to fertilize the 100% N level accordingly. 2.. Determine the effectiveness of three nitrogen injection rates with DI and SDI on maintaining adequate N levels in maturing pomegranates. Yearly, whole tree harvesting and analyses for total nitrogen (and other nutrients) will provide total N-uptake from three N application levels. 3. Determine the effect of real time seasonal nitrogen injections (N) with DI- and SDI-irrigated maturing pomegranate on N leaching losses. Soil samples will be collected down to two meters and analyzed for soluble N concentration and to determine the treatment effects on N-leaching losses. 4. Develop fertigation management tools that will allow the growers to achieve objective 1 and present these results to interested parties at yearly held field days and seminars. 5. Determine if concentrations of macronutrients (P, K, Ca, Mg) and micronutrients (Zn, Cu, Mn, Fe, B, Se) and eventually healthy bioactive compounds in soil, peel and fruit are influenced by precise N-fertigation management with DI and SDI. 6. Soil matric potential measurements will be used in the lysimeter to determine the direction of the hydraulic gradient and the N-leaching potential. 7. Development of fertigation management tools will be initiated for the first three years. These tools will eventually allow the growers to achieve the objectives and goals of this project. The obtained results will be presented to interested parties at field days and seminars.

3 Figure1. Plot layout of pomegranate fertilization project. 1. Soil sampling: The pre-irrigation and pre-fertigation mean soil nitrate in the plots for the three N-treatment levels are given in figure 2. There is a very consistent pattern of very low levels of nitrate-n in the soil profile to a depth of approximately 4 feet with the concentrations increasing at 6 feet and above the hard pan. This field has not been cropped for 2 years prior to planting the pomegranate and no fertilizer had been added prior to the planting of pomegranate in The larger amount of winter rainfall may have caused leaching of NO 3 -N to occur. The NO 3 -N increase with depth below 40 in. demonstrates a confining layer at a depth ranging between 5 and 6 feet. The uniform low levels of NO 3 -N in the top 3-4 ft. of the soil profile will insure that the trees will be responding to the imposed N treatments and not significantly to residual NO 3 -N in the soil. 2. Control System: Figure 3 shows the headwork s computerized-automated control system for scheduling the orchard irrigation and fertigation based on the hourly lysimeter measurements of pomegranate evapotranspiration. Hourly evapotranspiration, rainfall, soil moisture and drainage are transmitted via radio communication from the lysimeter in the orchard.

4 Figure 2. Mean soil NO 3 -N sampled in each treatment and replication in April 2011, prior to starting fertigation. 3. Plant Tissue NO 3 -N and Response to ammonium nitrate (AN-20) fertigation: Most of the N-uptake by plants is in the NO 3 -N form because of its solubility and mobility with water from the soil to the plant. We will use total N analysis to characterize the long term N response in addition to leaf NO 3 -N to measure rapid response to the N treatments. Most of the N in soil is lost as NO 3 -N leaching and denitrification as NO, N 2 O and N 2. Some NO 3 -N may also become immobilized by organic matter and thus not be available to plant uptake. Ammonium-N (NH 4 ) is also converted to NO 3 -N by nitrification bacteria. The use of high frequency drip irrigation/fertigation method minimizes soil water saturation that causes soil anaerobic conditions and leaching losses of NO 3 -N. It also attempts to match the applied mass of NO 3 -N to that required to meet plant requirements. Figure 4 shows means of tissue NO 3 -N sampled in each block of each treatment from May 4 to July 27, 2011 and the response to ten AN-20 fertigation events between June 17 and June 24, 2011 at an N concentration of 1.12 mg N/ml H 2 O. Although the applied N concentration was extremely small, tissue samples indicate a significant response to this fertigation and thus a potential for achieving the nitrogen fertigation objectives of this project. 4. Pomegranate canopy light interception measurements: Table 1 shows the plant canopy light interception obtained in August In 2012 light interception will be measured frequently throughout the growing season and related to ETc from the lysimeter to help generate crop coefficients (Kc).

5 Figure 3. The headwork s automated control system for scheduling the orchard irrigation and fertigation based on the radio transmitted hourly lysimeter measurements of pomegranate evapotranspiration.

6 Figure 4. Means of tissue NO 3 -N sampled in each block of each treatment from May 4 to July 27, Note the uniformity of the NO 3 -N tissue levels following the AN-20 injections. 5. Applied Fertilizers: Table 2 gives the total applied fertilizers in The application was uniform across all treatments to facilitate a uniform stand establishment. In 2012, differential N treatments will be initiated. 6. Cumulative ETo, ETc, Rainfall, crop water use, crop coefficients and water balance for young pomegranates: Figure 5 shows the cumulative reference ETo (CIMIS), rainfall P (CIMIS), lysimeter water loss (ET c + drainage) and adjusted crop coefficient (K c =ET c /ET s ) from April 28 to December 28, There was a total of 10.4 in. (264 mm) of rain during 2011 with only 3.2 inches (81 mm) occurring during the period from May 1 to December 28, There was a large residual stored soil water from rain early in the year that was available for early crop water use, thus irrigation began May 5. Figure 6 shows a total of 8.49 inches (216 mm) of applied irrigation water and the total crop evapotranspiration was estimated at 9.8 inches (249 mm). The difference was made up by stored soil water. In Figure 5, the lysimeter shows a total of 21.9 inches of loss. However, this number has to be modified to reflect the orchard tree spacing. The area associated with an individual tree is m² while the lysimeter area is only 8 m². The ratio of 8/ (0.4485) is necessary to adjust the lysimeter ET to reflect the actual crop ET. Thus, there is only a total of 9.8 inches of evapotranspiration and drainage allocated to the orchard trees.

7 Table 1. Pomegranate canopy light interception obtained in August 2011 (UCCE Presentation. Table 2. Fertilizer injected uniformly to the whole orchard in Figure 7 provides verification of the lysimeter weighing accuracy by exactly matching the 1.5 mm of rainfall measured by the calibrated rain gauge installed next to the lysimeter to the weight gain measured by the lysimeter at 22:00 PM when the etc was zero. The lysimeter datalogger is now connected via radio to the irrigation control system at the headworks pad. Real time hourly ETc from the lysimeter is now used to irrigate the orchard on an hourly basis, as needed. 7. Effects of poor quality water on nutritional content in pomegranates. In addition to the trees planted in the orchard (Fig. 1), pomegranate trees (v. Wonderful) were planted at the same time in large containers in a similar configuration at the SJVASC. The trees were irrigated with typical water qualities present in the Westside of the California Central Valley and effects on different nutritional parameters were evaluated from fruit harvested in Irrigation waters consisted of salinity ranging from 1 to 6 ds/m, and having boron and selenium (Se) concentrations of 4 mg/l and 0.25 mg/l, respectively. Trees were irrigated

8 individually with respective water treatment under micro-plot field conditions in Parlier, CA based in part by weather data collected from CIMIS. Results showed that vitamin C levels (Figure 8) and most total phenolic levels (Figure 9) increased in the fruit with irrigation water containing selenium, boron, or salinity. Macronutrient concentrations, e.g., Ca, Mg, K, P, S, and Se also increased in the fruit when poor quality waters were used (Tables 3 and 4). These increases in nutrient content were not observed in the seeds, except for Se. In the leaf samples collected from each treatment, the most significant increase was observed for Se concentrations. These preliminary results indicate that waters of poor quality may actually improve the nutritional content of young pomegranate fruit. This observation may be useful for growers of pomegranates on the Westside of central California. Figure 5. Cumulative ETo, ETc (including drainage), precipitation, and adjusted crop coefficient (Kc) for young pomegranates growing in the lysimeter. 8. Discussion/Conclusions: The initial results from the nitrogen sampling of plant tissues indicate that pomegranate is very responsive to nitrogen fertilizer. Additional studies with suction cup samplers have demonstrated that there is very little percolation loss resulting from either the surface or subsurface drip irrigation. The initial results from the nitrate analysis in the soils demonstrated that we have reasonably uniform nitrogen levels that will not impact the results in subsequent years of the study. The water balance studies demonstrated that the lysimeter system is working very well and will provide adequate data for characterizing the crop water use during the season. In discussions with other scientists the general conclusion is that there is very little information regarding actual crop water use from pomegranate, thus, these data will fill in a large gap in the existing literature on pomegranate crop water use and fertility requirements. A late-season study that characterized the shaded area under the crop (Table 1) demonstrated that the subsurface drip irrigated trees had

9 a larger canopy than the surface drip irrigated trees. This may be an indication of the differences in availability of water for plant development. Fruit were taken from the trees and discarded to prevent damage to the trees. Next year data will be collected on fruit numbers and size in response to the fertilizer treatments. Changes in vitamin C, phenolics and nutrient concentrations, as affected by irrigation water qualities, were observed in the seeds, flesh and the leaf samples collected from separate experimental treatments. These preliminary results indicate that waters of poor quality may actually improve the nutritional content of young pomegranate fruit. This observation may be useful for growers of pomegranates on the Westside of California Central Valley. A website was initiated to provide real time information to interested parties. The website is accessible at: ( Follow the link to Research and Extension Projects and then go to Horticulture and select Pomegranate Lysimeter Project. Figure 6. Cumulative irrigations and crop coefficient for the pomegranate in the orchard.

10 Figure 7. Lysimeter weighing accuracy is demonstrated by exactly matching the 1.5 mm of rainfall measured by the calibrated raingauge installed next to the lysimeter to the weight gain measured by the lysimeter at 22:00 PM when the ET c was zero.

11 Figure 8. Effects of water quality on Vitamin C level of pomegranate.

12 Figure 9. Effect of water quality on total phenolics levels of pomegranate

13 Table 3. Effect of 7 water qualities on flesh and seed contents of Ca, Mg, K and P. Table 4. Effect of 7 water qualities on on flesh and seed contents of S, Na, Cu, Fe, Mn, Zn and Se. 9. Acknowledgements: The following companies have contributed to this project. Paramount Farming trees Toro Microirrigation drip tubing Lakos filter set Dorot Electronic Control Valves Verdegaal Brothers - fertilizer SDI + -Consulting time and miscellaneous equipment AGQ Leaf N analysis, deep percolation N analysis