2013 Evaluation of Blackeyes as a Rotational Crop under Subsurface Drip Irrigation

Transcription

1 2013 Evaluation of Blackeyes as a Rotational Crop under Subsurface Drip Irrigation Introduction C.A. Frate 1 andl.j. Schwankl 2, Katherine Wilson 1,Walter Martinez 1, and Yvonne Lopez 1 Subsurface drip irrigation () is being used on increasing numbersof acres on the west side of California s San Joaquin Valley for tomatoes andcotton. Although the economic return from blackeye cowpeas would not justify installation of subsurface drip for their own sake, growers who already have for other crops might want to plant blackeyes in the field rotation. For research purposes, the amount of water applied is easier to control with subsurface drip compared to furrow irrigation, making it easier in trials to evaluate the impacts of different timing and amount of water on blackeye production. As reported in the Progress Report for 2012, drip lines were placed directly under each 30-inch bed in that year. Applied water, not including approximately 4 inches stored in the root zone from the pre-irrigation, ranged from almost 12 inches to 22 inches representing from 67% to 125% ET. There were no differences in yield or quality among the treatments. In the 2013 trial,the drip tape was placed 10 inches below the surface in the center of a 60 inch bed. Two plant rows were planted per bed, each about inches laterally from the drip line. Drip treatments of 50%, 75%, 50% pre-bloom followed by 100% ET, and 100% ET were compared to a 100% ET280ft furrow irrigation run. Trial Design and Treatments The trial was located at the UC Kearney Research and Extension Center, Parlier, CA, in a Hesperia coarse loam soil.the trial was a randomized block design with 4 replications. For the furrow irrigated treatment, there were six 30-inch beds per plot. Each plot extended approximately 280 ft to the end of the field. Subsurface drip irrigation ()plots were three 60- in beds wide. Each bed had a row of beans on each shoulder with a drip line at a depth of 10 inches in the center of the bed. The two rows of beans were about inches laterally from the drip line and about inches apart from each other. plots were only 200 ft long to save on the cost of drip tape. The intended treatments were: A. Furrow irrigation on 30-inch beds to represent standard practices in commercial fields B. targeted to apply 50% of estimated evapotranspiration (ET) throughout the season C. targeted to apply 75% of estimated ET throughout the season D. targeted to apply 50% estimated ET until flower bud followed by 100% of estimated ET 1 C.A. Frate, K. Wilson,W. Martinez and Y. Lopez, UC Cooperative Extension, Tulare County, 4437 S. Laspina St., Tulare Ca 93274; 2 L.J. Schwankl, Dept. of Land, Air & Water Resources, UC Davis located at, Kearney Research & Extension Center; 3. cafrate@ucanr.edu, IN: University of California Dry Bean Research 2013 Progress Report published by the California Dry Bean Advisory Board, 531-D North Alta Avenue, Dinuba CA and online at: 53

2 E. targeted to apply 100% estimated ET throughout the season Field preparation and stand establishmentthe field was fallow during a relatively dry winter and soil was quite dry in April. After a soil test indicated that the field was low in phosphorus and potassium,300 lbs/a of and 500 lbs/a of potassium sulfatewere applied and incorporated. Then 30-inch beds were formed throughout the field. For the furrow irrigated treatment with the standard one row of beans per 30 inch bed, a preirrigation occurred on May 7 in addition to 1 inch of rain on the same pt/aand Prowl H2O@1.5 pt/a were applied and incorporated on May 15. On May 17, CB 46 seed was planted into very good moisture. For the subsurface drip irrigated treatments, the next step after forming 30-in beds was tocombine two 30-in beds into one 60-in bed. Bowsmith BigFoot drip tape, 5/8 ID, 8 mil with 12 emitter spacing and a flow rate of 0.45 gpm/100 ft, at 8 psi was placed in the center of the wide bed 10 inches below the top of the bed. On May 7 it rained an inch but the soil had been so dry that the herbicides pt/a and Prowl H2O@1.5 pt/a) could be applied by ground the following day. Beds were then sprinkler irrigated to set the herbicides and to supply water for planting into moisture. Two replications were sprinkled with 3/8 in. on the next day and the remaining replications two days later on May 10. The goal was to plant both furrow and drip treatments the same day. Cool weather delayed drying of the furrow irrigated beds and planter problems delayed planting until May 17. By that time, a firm crust had developed on the 60-in beds and moisture was variable. Seeds of CB 46 were placed as deep as possible (about inches) with the available planter. Soil temperatures for both furrow and drip treatments were in the 80 s o F in the afternoon. By May 24 the stand was excellent in all the furrow irrigated beds but very spotty on the 60-in drip irrigated beds. It was unknown if running the subsurface drip tape could wet the bed shoulders so to improve seedling emergence the drip beds were furrow irrigated, hoping that water could sub to the seed rows on the edges of the beds, reduce the crust, and provide moisture to seed that might have been placed in dry soil. This irrigation wet the soil profile, Table 1. Estimated plant populations by treatment, 2013 Blackeye Trial, UC Kearney Agricultural Research and Extension Center, CA Treatment A. Furrow irrigation Plant Population per Acre 45,563 a B. 50% ET 29,082 b C. 75% ET 32,148 b D. Drip 50% ET then 100% ET 27,496 b E. 100% ET 27,767 b P-Value LSD (0.05) CV (%) , Means are the average of 4 replications. Values within a column followed by a common letter do not differ at the 5% level of probability. 54

3 increasing the water available to plants and eliminating our ability to induce early season stress in the 50% stress pre- flower bud treatment. It also delayed the imposition of 75% ET treatment. Stands were only partially improved. After stands were as good as they were going to get, plant populations were evaluated by counting seedlings in four 8.7 ft lengths in each of the 6 rows/treatment and calculating plants per acre (Table 1). Insects A population of cowpea aphids developed in mid-june requiring a spray application of Warrior II (1.92 fl.oz./a) on June 26. Pressure from lygus bugs was very high in July and early August. Spray applications were made on July 16 (Lannate 1 lb/a), July 25 (Lannate 1 lb/a), August 8 (Macho 2,8 oz/a), August 28 (Lannate 1 lb/a), and Sept. 6 (Macho 2.8 oz/a). Despite numerous sprays, lygus bugs counts were above recommended threshold levels in late July and early August (Table 2 ). Evidence of aborted flowers on the pedicels was observed in all plots. Table 2. Lygus bug counts, 2013 blackeye trial, UC Kearney Agricultural Research and Extension Center, Parlier, CA. Number of lygus bugs per 10 sweeps Treatment 7/29 8/1 8/7 8/12 8/19 8/22 9/13 9/16 9/23 Furrow irrigation a % ET a % ET a Drip 50% ET then 100% ET b % ET a P-Value LSD (0.05) NS NS NS NS 2.86 NS NS NS NS CV (%) Means are the average of 4 replications. Values within a column followed by a common letter do not differ at the 5% level of probability. Applied water, soil moisture monitoring and ET The blackeye ET used as the standard was that detailed by W.R. DeTar in his publication Crop coefficients and water use for cowpea in the San Joaquin Valley of California. 2 The DeTar crop coefficients (Kc) were used with the reference ET (ETo) values from the CIMIS (California Irrigation Management Information System) station located on the Kearney Research and Extension Center. Crop ET was determined as: ETcrop = ETo x Kc The applied water, by treatment, is shown in Table 3 along with the estimated blackeye evapotranspiration. 2 DeTar, W.R Crop coefficients and water use for cowpea in the San Joaquin Valley of California. Agricultural Water Management 96 (2009)

4 Table 3. Summary of the seasonal estimated crop ET and the irrigation amounts for each of the treatments, 2013 blackeye trial, UC Kearney Agricultural Research and Extension Center, Parlier, CA Estimated Blackeye ET (in) 50% ET 75% ET 100% ET 50% ET 75% ET Applied Water (in) 50/100% ET 100% ET Furrow It is difficult to exactly match the selected irrigation treatments, especially with furrow irrigation, but we were relatively successful. The amount of water applied to the 50% ET treatment was 51% ET, to the 75% ET treatment turned out to be 80% ET, to the 50% / 100% was 53% / 101% ET and to the 100% ET treatment was 104% ET. To account for any change in soil moisture from the beginning to the end of the season, we collected soil samples at multiple locations in the field to a depth of 5 feet. At all sampling sites, the end-of-season, stored soil moisture was less than it was pre-season. Examining the soil moisture sensor information would lead to the same conclusion. The decrease in soil moisture across the season indicates that the soil is providing some of the water to meet crop ET. The seasonal irrigation applications and soil water contributions are summarized in Table 4. Table 4. Summary of the seasonal estimated crop ET, irrigation amounts and soil water contribution for each of the irrigation treatments, 2013 blackeye trial, UC Kearney Agricultural Research and Extension Center, Parlier, CA Estimated Blackeye ET (in) 50% ET 75% ET 100% ET Applied Water (in) + Soil Water Contribution (in) 50% ET 75% ET 50/100% ET 100% ET Furrow Accounting for the contribution of the stored soil moisture, the final ET for each treatment was: 59% ET, 88% ET, 53% / 103% ET, 108% ET, and 118% ET Furrow. To help understand the water status in the root zone during the season, Irrometer Watermark soil moisture blocks were installed in the plantrowat 6, 18, 30, 42, and 54 inch depths in each treatment in the third replication. However, in the 75% ET treatment, due to a hardpan, only the 6, 18 and 30 inch depths could be installed and in the 75% ET treatment, moisture blocks could only be installed to 42 inches. Soil moisture blocks were connected to a Watermark data logger that collected readings every 8 hours. Graphs of the soil moisture for each treatment are shown in figures at the end of this report. 56

5 50% ET (Figure 1)The early-season soil moisture in the first foot of soil depth decreased from the beginning of the season to the beginning of July, at which point the soil moisture stabilized. At the beginning of August, the first foot soil moisture block indicates that the soil moisture in the first foot increased. Examination of the irrigation events do not indicate a reason for this change although there was a larger than usual irrigation at the end of July which may have been the cause. The soil moisture blocks at the second, third, and fourth foot all indicate a slight drying trend from the beginning of the season to the first part of August. During the first 3 weeks of August, the 6-inch and 18-inch blocks indicated that the soil moisture stayed constant or increase slightly. The third and fourth foot blocks indicate constant soil moisture at these depths. Starting the last week of August, the soil moisture block in the first foot indicated that the soil was drying significantly. Likewise, the blocks in the second, third, and fourth foot showed a constant drying trend. Part of this is explained by noting that the last irrigation was on 9/16/13 and the last furrow irrigation was 9/18/13. Irrigation was cut off at those times to allow the soil to dry down prior to cutting on 10/2/13. 75% ET (Figure 2)Soil moisture blocks were only installed in the top 3 feet due to a hardpan layer that could not be penetrated. While there were some soil moisture fluctuations, blocks at all 3 depths showed a gradual drying trend across the season with the rate of soil drying increasing after irrigation was terminated on September 16. This season-long soil moisture depletion is as expected since only supplying a portion (actual applications were 80% of ET) of the plant's water needs (ET) would result in the blackeyes mining some of the stored soil moisture. 50% ET / 100% ET (Figure 3)This soil moisture plot is reflective of the irrigation practices. Until bloom (7/2/13), irrigations were 50% of estimated ET. This resulted in a drying of the first foot of soil and a slight drying of the second foot. After bloom irrigations were 100% of ET and the first foot of soil moisture recovered and stayed near field capacity for the rest of the irrigation period. The first foot again started to dry after irrigation was cut off on September 16. The second, third, fourth, and fifth foot of soil all remained near field capacity for the entire season, only drying after irrigations were cut off. Irrigation satisfied crop water demands, without the need for the plant to utilize stored soil moisture, until the end of the season when irrigation was stopped. 100% ET (Figure 4)This is a difficult plot to explain, particularly after examining the 50% ET/100% ET treatment area. After July 1, these two treatments (50% / 100% ET and 100% ET ) received the same amount of water. While the 50% ET/100% ET treatment's moisture block plots show the soil staying near field capacity throughout the season, the 100% ET treatment shows a significant first foot drying until the beginning of August. Following that, the soil moisture in the first foot stayed near field capacity until irrigations were cut off on September 16. A possible explanation is that the water from the drip tape, at a 10 inch depth and in the center of the bed, was not reaching the moisture block located at a 6 inch depth on the 57

6 shoulder of the bed. A larger irrigation and at the end of July finally pushed the water to the block. The second foot soil moisture block shows some of the same pattern as the first foot block, although not to as great an extent. The third, fourth, and fifth foot soil moisture blocks show little change across the season until irrigations were cut off on September 16, after which they show a slow drying trend. 100% ET Furrow (Figure 5)The blocks at the first and second foot of soil depth exhibit the typical drying and rewetting pattern associated with furrow irrigation. Because of the shorter field length and difficulty in getting more than about 2 inches of water in any irrigation to penetrate due to a prevalent soil sealing problem common to the Kearney Ag Center soils, irrigations were done weekly. At the third, fourth, and fifth foot soil depths, there was a very slight drying across the season. It is evident that the irrigation amounts satisfied crop ET and except for the end of the season after irrigation was cut off (September 18), there was little mining of stored soil moisture. Yield and Quality Beans were cut on October 2 with a commercial type cutter. Care was needed to avoid slicing the connecting hose from the main line to the drip tape as the blades cut into the 60-in beds. Yield data was collected from a 100 ft section from the center two rows of each plot.in the case of the treatments, this meant the data was from both rows on the center bed. Beans were threshed on October 25. Yield data were based on the weight of seed per plot after sifting twice to remove large debris. A seed splitter was used to obtain 2-2.5lbsub-samples that were then passed through several smaller screens. All seeds passed through the 22/64 screen; all but a very few went through the 20/64. Most of the seed did not pass through the 11/64 x ¾ oblong screen but dirt and peewees fell through. A 100 gram subsample of the seed caught on the 11/64 x ¾ oblong screen was evaluated for lygus damage, splits, and trash. Each blackeye seed in the 100 gram sample was evaluated and sorted into one of six categories: no damage, 1 lygus sting, 2 or more lygus stings, worm damage, stained or split, or trash. After seeds were sorted, each category was weighed and beans were counted. Yield results need to be considered very cautiously. Lygus bugs exceeded the thresholds on several occasions so total yield was most likely reduced, although the data would suggest there was not a strong influence of treatment on lygus bug counts. It is really unjustified to compare the furrow irrigation to the drip treatments for two reasons. The furrow irrigation in this trial was unusually efficient and timely compared to commercial fields. In order not to stress the furrow treatment and thereby put it at a disadvantage relative to drip treatments, water was run on a weekly basis. Thelength of the run was only 300 ft and the amount of water applied closely matched ET. In commercial fields, water cannot always be applied on such a timely basis and the amount appliedin order to get water from one end of the field to another is usually larger than needed to replace ET. The result is that water in the furrow treatment was applied about as efficiently as drip irrigation. The second reason to avoid comparing the furrow to drip treatments is the significantly better stand in the furrow treatments. 58

7 When comparing the yield response of the drip treatments (Table 5) it is important to recall that a furrow irrigation was run shortly after planting to improve the stand. This irrigation filled the soil profile providing a reservoir of water for all of the treatments and eliminating the pre-bloom stress in the 50%/100% ET treatment. Among the drip treatments, the only difference among treatments was that the 50% ET treatment produced significantly more than the 100% ET treatment. Table 5. Yield results, 2013 blackeye trial, UC Kearney Agricultural Research and Extension Center, Parlier, CA Yield (lbs/a) 50% ET Clean Weight 2,445 75% ET 2,323 abc 50% ET followed by 100% ET 2, % ET 1,953 c P-Value LSD (0.05) CV (%) Furrow treatment produced 2546 lbs/a, significantly higher than the 50%/100% and the 100% ET treatments, but is not included in the table as it had a significantly better plant stand than all treatments. Means are the average of 4 replications. Values within a column followed by a common letter do not differ at the 5% level of probability. Quality data is summarized in Table 6.Seed damage due to lygus bugs or worms did not differ among the treatments. Splits also were not significantly different among the treatments. Seed size tended to weigh less with the 75% ET and 100% ET treatments compared to the 50% ET and the furrow treatments. 59

8 Table 6. Seed weight and insect damage, 2013 blackeye trial, UC Kearney Agricultural Research and Extension Center, Parlier, CA No Damage 1 Lygus Sting % by Total Weight 2 or More Lygus Stings Worm Damage Stained or Split Treatment Grams per bean Furrow irrigation 0.22 a % ET 0.23 a % ET 0.22 ab % ET followed by 100% ET 0.21 b % ET 0.21 b P-Value LSD (0.05) 0.01 NS NS NS NS NS CV (%) Means are the average of 4 replications. Values within a column followed by a common letter do not differ at the 5% level of probablity. Summary and Discussion There were two issues with the trial this year that compromised our objectives. First was the early furrow irrigation that was conducted to try to improve the plant stand in the treatments. This irrigation provided sufficient soil moisture to eliminate early season stress in plots irrigated at less than 100% ET. Secondly, even with the furrow irrigation, the stands in all the treatments were variable and less than optimum. With early season furrow irrigation and a less than optimum stand, the 50% ET irrigation regime produced 2445 lbs per acre using a total of 14 inches of water. Based on this trial and last year s, there is reason to further investigate blackeye production using subsurface drip. In particular, it would be good to do so without the benefit of a pre or early season furrow irrigation. At this point, there is not enough confidence to recommend a 50-75% ET irrigation regime with in blackeyes or to depend on reaching maximum yields with a 50 or 75% ET regime. But it seems that this crop has potential to produce well with inches of water. Further trials are desirable to evaluate the impact of these regimes without furrow irrigation either prior to planting (2012) or after planting to help establish a stand (2013). Because of the problems incurred with establishing the stand in this trial, we conducted a small test in some adjoining 60-inch beds to determine if a stand could be established using just water from the subsurface drip system. Results are reported in the next article. Weed control in this trial appeared to be very good with the Dual + Prowl application followed by sprinkler irrigation but there was no area left untreated to evaluate weed pressure. No phytotoxicity was observed on the blackeyes. One of the challenges of with blackeye cowpeas is that there are no broadleaf herbicides registered for post emergence weed control. Currently, there are post emergence herbicides for grass control but for broadleaves the herbicides are generally pre-plant mechanically incorporated, usually after pre-irrigation. ************* 60

9 We gratefully acknowledge and thank the field staff at the UC Kearney Research and Extension Center without whose assistance we could not have conducted this trial. We also thank Cal-Bean & Grain, Pixley CA, who provided seed and Rhizobia inoculum. 61

10 Figure season soil moisture levels in the 50% ET irrigation treatment. The soil moisture was monitored using Watermark soil blocks connected to a Watermark data logger. Figure season soil moisture levels in the 75% ET irrigation treatment. The soil moisture was monitored using Watermark soil blocks connected to a Watermark data logger. 62

11 Figure season soil moisture levels in the 50% pre flower bud and then 100% ET irrigation treatment. The soil moisture was monitored using Watermark soil blocks connected to a Watermark data logger. Figure season soil moisture levels in the 100% ET irrigation treatment. The soil moisture was monitored using Watermark soil blocks connected to a Watermark data logger. 63

12 Figure season soil moisture levels in the furrow irrigation treatment. The soil moisture was monitored using Watermark soil blocks connected to a Watermark data logger. 64