published april 19, 2013 dry beans · 2017. 3. 21. · 0.33, 0.67, 1.00, and 1.33 of estimated...

Dry Beans

Dry Bean Yield Response to Different Irrigation Rates in Southwestern Colorado Mahdi M. Al-Kaisi, Abdel E Berrada, Mark FK Stack

Research Question

Literature Summary

Study Description

Applied Questions

Concerns about irrigation efficiency, water quality, and yield have prompted this study. Over-irrigation is a key factor that contributes to deep percolation and nutrient leaching to the groundwater. The objective of this study was to determine the effect of five different irrigation rates on dry bean yield response and water use efficiency.

The dry bean is very sensitive to irrigation management. Studies indicate that dry bean yields can vary significantly as irrigation rates go from dryland to optimal rates. However, the increase in yield may not be significant with the increase of the irrigation rate beyond optimum water need. It was reported that dry bean can extract water from the soil profile much deeper under dry and’limited-irrigation conditions than over-irrigated conditions.

The field study was conducted to investigate the impact of five irrigation rates on dry bean growth response. The irrigation rates used in this study were 0.00, 0.33, 0.67, 1.00, and 1.33 of estimated evapotranspiration (ET). The soil on the site is Wetherill silty clay loam. The experiment was a randomized block design with four replications. A surface drip irrigation system was used to achieve the complete designed irrigation rates. An irrigation scheduling program was used to manage irrigation. Weather data from a local weather station on the site was used to estimate ET by using the Penman Equation. The water balance approach was used to determine the 1 .OOET irrigation rate based on estimated ET, precipitation (total seasonal precipitation was 7.6 and 5.0 in. from June to September of 1992 and 1994, respectively), change in soil moisture, runoff, and drainage terms in the 1992 and 1994 seasons.

How does dry bean respond to different irrigation rates?

Seed yield and dry matter increased significantly as the irrigation rates were increased up to the optimal water use (1 .OOET) in 1994. However, maximum seed yield was obtained at 0.67ET in the cooler year (1992), while 1.00ET or greater was required to achieve maximum biomass yield in both years. Improvement in the yield was related to the water and irrigation use efficiencies, where yield production (seed or dry matter) per 1 in. of applied or used water was greater when the irrigation rate was kept at or below 1.00ET. Therefore, exceeding plant water requirements not only leads to waste of water, but also can affect plant performance and soil environment.

What is the impact of the irrigation rate on soil water use or root moisture extraction pattern?

Over-irrigation encouraged a shallow root system. The effective root depth under an irrigation rate greater than 1 .OOET was 12 in. Conversely, limited irri-

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Full scientific article from which this summary was written begins on page 422 of this issue.

J. Prod. Agric., Vol. 12, no. 3,1999 347

Published April 19, 2013

Recommendation

gation treatments encouraged the development of a deeper root system and water uptake down to 3-ft. Also, the soil moisture profile under over-imgated and 1 .OOET was close to field capacity during the growing season, which may lead to potential deep percolation and nutrient loss to the groundwater.

Dry bean production in semi-arid climate areas like southwestem Colorado can be improved significantly by using proper imgation scheduling. Irrigation scheduling can improve irrigation and water use efficiencies, especially in areas such as southwestern Colorado, where water management is critical to crop yield and water quality. The dry bean root system can use soil moisture more efficiently from lower depths (24 in. or deeper) when optimum imgation was applied (equal to or less than 1 .OOET). However, the irrigation scheduling program (SCHED) may have overestimated water requirements in the cooler year to achieve maximum seed yield, while predicting the water requirements need- ed for maximum biomass yield at 1 .OOET or greater in both years.

1

348 J. Prod. Agrie., Vol. 12, no. 3,1999

Dry BeansDry Bean Yield Response to Different Irrigation Rates

in Southwestern ColoradoMahdi M. Al-Kaisi,* Abdel F. Berrada, Mark W. Stack

The dry bean (Phaseolus vulgaris L.) crop is sensitive to irri-gation management. Irrigation efficiency, water quality, andyield production are concerns in southwestern Colorado. Thisfield study was conducted in 1992 and 1994 at theSouthwestern Colorado Research Center to study the effects offive irrigation rates on dry bean seed yield and dry matter. Thesoil on the site is Wetherill silty clay loam (fine-silty, mixed,superactive, mesic, aridic haplustalf). A surface drip irrigationsystem was used to achieve the irrigation rates of 0.00, 0.33,0.67, 1.00, and 1.33 of the estimated evapotranspiration (ET).The experiment was set up using a randomized complete blockdesign with four replications. Optimum conditions during the1992 season led to higher dry matter and seed yields than in1994. Irrigation rates had a significant effect on total above-ground dry matter (TDM) and seed yield in both years. Therewas no significant increase in seed yield and TDM beyond0.67ET and l.OOET, respectively, in 1992. However, maximumseed yield was obtained at a 0.67ET irrigation rate in the cool-er year (1992), while l.OOET or greater was required to achievemaximum biomass yield in both years. Total DM and seed yield

M.M. AI-Kaisi, Colorado State Univ. Coop. Ext., U.S. Central Great PlainsRes. Stn., 40335 County Road GG, Akron, CO, 80720; A.F. Berrada andM.W. Stack, Southwestern Colorado Res. Cent, Yellow Jacket, CO 81335.Received 13 Dec. 1998. "Corresponding author (970/345-2259, fax -0502,[email protected]).

Published in J. Prod. Agric. 12:422^127 (1999).

422 J. Prod. Agric., Vol. 12, no. 3, 1999

continued to increase up to 1.33ET in 1994, reaching a similarlevel as in 1992. Irrigation use efficiency declined as the irriga-tion rate increased in both years. The pattern of biomass accu-mulation was similar in 1992 and 1994, as more growthoccurred with the greater irrigation rates. Visual observationsrevealed a shallower root system under the higher irrigationrates than under the nonirrigated (O.OOET) and the limited-irrigation (0.33ET) treatments. This was confirmed by the soilmoisture profile at harvest in 1992 and 1994. Dry bean canextract soil water from the 0 to 24 in. soil profile under drylandconditions, and from the 0 to 12 in. soil profile under well-irri-gated conditions (l.OOET). Soil moisture content below 12 in.was at or near field capacity under the over-irrigation treat-ment (1.33ET), which suggests the potential for deep percola-tion and leaching of nitrates and other soluble salts. Over-irri-gation appears to encourage a shallow root system, less than 2ft. (field plant root inspection), which may reduce the use of soilmoisture at lower depths and encourage deep percolation tothe groundwater.

I!RRIGATION PROVIDES the means to optimize plant water useand to increase crop production in many areas.

Abbreviations: ET, evapotranspiration; ETWUE, water use efficiency; HI,harvest index; IWUE, irrigation water use efficiency; SYd .̂, nonirrigateddry bean seed yield; SY(, irrigated dry bean seed yield; TDM, total above-ground dry matter; TOM,̂ , nonirrigated total dry matter; TDMj, irrigatedtotal dry matter.

Implementing sound irrigation water management practices is necessary to overcome excessive irrigation and eliminate many associated problems, such as nutrient leaching and surface runoff. This concept is critically important in areas such as southwestern Colorado, where deep percolation associated with over-irrigation combines with a saline geo- logical formation (Mancos Shale), which contributes heavi- ly to the salinity problem in the Colorado River. Therefore, irrigation scheduling becomes a crucial element in reducing deep percolation and improving water quality downstream. Another consideration is the efficiency of the water delivery system of the Dolores River Project, which was estimated at 87% compared with the actual water delivery efficiency of the McPhee Reservoir (97%), due to water losses as seepage and evaporation.

Many researchers have investigated the relationship between yield and crop water use. The dry bean has been found to be sensitive to water stress. Singh (1995) reported that water stress during flowering and grain filling reduced seed yield and seed weight, and advanced the maturity of the dry bean. Irrigation efficiency is an issue in southwestern Colorado due to the salinity problems associated with irrigated agriculture and their impact on crop production. The dry bean is sensitive to salinity and water availability. Several studies have examined the impact of soil moisture status on dry bean production. In a study conducted by Howe and Rhoades (1961), yields of dry bean varied by 1269 lb/acre when the number of fbrrow irrigations ranged from one to four. The water requirement for the dry bean is approximately 17 in. of water per season in southwestern Colorado (Schwartz et al., 1996). The low water use by the dry bean provides an opportunity to reduce over-irrigation, compared with other crops grown in southwestern Colorado. Therefore, increasing the acreage in dry bean and small grain production, and decreasing the acreage in alfal- fa (Medicago sativa L.), would help avoid water shortages in dry years in the area. However, the production costs, mar- ket availability, and price dictate what crop farmers grow.

Soil moisture affects nutrient availability to crops and their yield response. In studies by Miller and Burke (1983), it was found that dry bean yield increased linearly with the increase in water application rates. Also, Stegman and Olson (1976) on pinto bean found a linear relationship between yield and estimated water use. There have been numerous studies on bean response to soil moisture. Miller and Burke (1983), Pandey et al. (1984), and Turk et al. (1980) used the line source irrigation system developed by Hanks et al. (1976) to study the yield response of crops such as dry bean and cowpea [Kgna unguiculata (L.) Walp. subsp. unguiculata]. It was found that different grain legumes respond differently to irrigation variability. Also, it was found that yield increased with water applied up to 1 .OOET. Nielsen and Nelson (1998) reported that black bean yields were most sensitive to water stress during the repro- ductive growth stage, and plant height and leaf area were most sensitive to water stress during the vegetative growth stage.

The top five counties in dry bean production in Colorado are Yuma, Weld, Kit Carson, Montrose, and Dolores. In 1997, 135 000 acres were planted with dry bean in Colorado under dry and imgated conditions. A total of 100 000 acres

are harvested under irrigation, with total production of 2 120 000 lb, and an average of 2 120 lb/acre. In contrast, the total harvested nonirrigated acreage in dry bean production was 20 000 acres, with an average yield of 800 lblacre (Colorado Department of Agriculture, 1998). However, this left 15 000 acres of the total planted acreage not harvested due to weather and other related conditions according to Colorado Agricultural Statistics Service (1 999, personal conversation). In southwest Colorado, which includes several counties including Montrose and Dolores Counties, the total acreage in dry bean is 44 500 acres, where 22 700 acres are under irrigation with an average yield of 2000 Ib/acre (Colorado Department of Agriculture, 1998). The very large dry bean acreage in irrigation in this area of Colorado, in particular, would benefit from the optimization of irrigation rates. This should improve yield, and most importantly, reduces over-irrigation that contributes to deep-water percolation and its impact on dissolving the natural salt formation (Mancos Shale) into the Colorado River.

The objective of this study was to determine the effect of five different irrigation rates on dry bean yield response and water use efficiency (ETWUE).

MATERIALS AND METHODS

The study was conducted during the growing seasons of 1992 and 1994 at the Southwestern Colorado Research Center at Yellow Jacket. The soil on the site is Wetherill silty clay loam. The experiment consisted of five irrigation rates, which were replicated four times in a randomized complete block design. The treatments were 0.00, 0.33, 0.67, 1.00, and 1.33 of estimated ET. Individual plot size was 15 by 20 ft. Plots of different treatments in each repli- cation were separated by a buffer zone 10-ft. wide and diked to contain the irrigation water and eliminate water runoff. Also, the same buffer zone (10 ft.) was established between replications for the same purpose. Soil moisture content was measured twice a week in the center of each plot by using a neutron probe (CPN model No. 503') at depths of 6, 12,24, 36, and 48 in.

Irrigation water was applied by using a drip system. The irrigation system consisted of a 2 in. internal diameter poly- ethylene tube connected to the main irrigation line. A filter was installed in the main line to prevent sediment from blocking the emitters. Five 0.5 in. internal diameter, 120-ft. long, lateral tubes were connected perpendicular to the poly- ethylene tube at 30 in. spacing on the top of the furrow beds. The drip irrigation system was designed to deliver four different rates of water: 0.13, 0.26, 0.38, and 0.51 in.h at 15 PSI with a 20 in. space between the emitters. Irrigation scheduling was done with the SCHED program (Buchleiter et al., 1988) using data collected from the local weather station to estimate daily crop water use. The SCHED program estimates crop water use by using the modified Penman Equation (Jensen et al., 1971), along with polynomial functions to generate crop coefficients based on the fraction of time from planting to full cover and days after full cover (Duke, 1987). Irrigation was applied using the manageable

*

Trade name is included for the benefit of the reader and does not imply any endorsement or preferential treatment of the product by the authors or csu.


Table 1. Combined analysis of variance of total dry matter and seed yield of the 1992 and 1994 dry bean growing seasons.

Table 2. Dry bean dry matter and seed yield as influenced by irrigation amount in the 1992 and 1994 growing seasons.

Source

F-value Pr>F

DF TDMt Seed TDM Seed ~~

Year 1 6.37 6.14 0.045 0.048 Error a: Rep (year) 6 1.79 1.28 0.150 0.308 Treatment 4 124.35 46.22 0.000 0.001 Error b Year X Treatment 4 0.80 1.28 0.536 0.309 Pooled error 24

t TDM =total above-ground dry matter.

allowable depletion, which refers to the acceptable soil moisture depletion (40-50% of available soil moisture) at different growth stages for the 1.00ET treatment by using the water balance approach, which includes estimated ET, soil moisture change, precipitation, and drainage to determine irrigation amount. The following water balance relationship was used in determining the irrigation amount:

I + P - R = ET + D + SW

where the terms on the left-hand side of the above equation represent the applied imgation water (I), precipitation (P), and surface runoff (R). The sum of these three terms represents the net addition of water to the soil profile over a time period of interest. On the right hand side of the equation are estimated ET, drainage or deep percolation (D), and the water storage change (SW) of the soil profile. Each of the terms in the above equation represents water flows or storage changes over some arbitrary time intervals. All of the terms in the equation are positive except for D and SW, which may be either positive or negative depending on the direction of the water flow (upward or downward flow) (Jury et al., 1991). Surface runoff (R) was negligible due to control of the water application on each plot. Deep percolation (D) did not occur, based on soil moisture monitoring at 4 to 5 ft depths, where no increase in soil moisture was found.

The dry bean (cv. Bill Z) was planted at 84 000 seeddacre on 7 June 1992 and 3 June 1994 with row spacing of 30 in. No N was applied in 1992, and 40 lb N/acre was applied in 1994 based on soil test results. Three pounds per acre of Eptam (S-ethyl dipropylthiocarbamate) and 0.25 lb ai/acre of Treflan (trifluralin) were incorporated into the soil before planting. Plant samples for dry matter were taken at different growth stages by cutting plant shoots at the ground level (two rows by 5 ft.). Half of each plot was harvested for dry matter yield determination. An area of 5 by 20 ft (two rows by 20 ft) from each plot was harvested for seed yield and final biomass yield assessment.

RESULTS AND DISCUSSION

Seed yield and dry matter were affected by different rates of irrigation. Combined analysis of variance revealed a significant difference in yield between the 1992 and 1994 growing seasons (Table .1). The seed yield and dry matter means for 1992 were 2802 lb/acre and 4582 lb/acre, respectively, compared with 2356 lb/acre and 3970 lb/acre, respectively, in 1994. This may be attributed to the weather differences between the 2 yr (temperature and precipitation). The

424 J. Prod. Agric., Vol. 12, no. 3,1999

Treatment Year

1992 0.00 ET 0.33 ET 0.67 ET 1 .OO ET 1.33 ET

1994 0.00 ET 0.33 ET 0.67 ET 1.00 ET 1.33 ET

Irrigation ET

in.-

0.0 3.0 4.5 7.0 9. I 11.3

13.1 15.3 18.6 20.6

0.0 2.8 5.3 6.0

10.6 11.6 16.1 17.3 21.4 23.0

-.

_____

TDMt Seed7

- Iblacre-

2087 a 1 1 1 1 a 3542b 1959b 4769c 3360c 6126d 3618c 6388d 3963c

11OOa 540 a 2698 b 1564 b 4115c 2270c 5633d 3517d 6302e 3891 e

t Means within columns within year followed by the same letter are not significantly different at alpha = 0.05 as tested by Duncan multiple range test.

amount of precipitation in 1992 (7 June to 14 Sept.) was 7.6 in., and total growing degree days were 1617, compared with 5.0 in. and 1899 total growing degree days in 1994 (3 June to 29 Aug.). In 1994, there were 13 d from planting to harvest during which the maximum temperature was greater than or equal to 90°F., and none in 1992. Higher tempera- tures and high evaporative demands during the growing season may lower the bean seed yields (Nielsen and Nelson, 1998).

Effect of Irrigation Rates on Yield and Dry Matter

In 1992, the yield of dry bean was much greater than in 1994, especially for O.OOET, 0.33ET, and 0.67ET treatments, where irrigation was limited. It seems that the cooler 1992 growing season contributed to higher yields compared with 1994 under limited irrigation (Nielsen and Nelson, 1998). Maximum seed yield was obtained in the cooler year (1992) at an irrigation rate equal to 0.67ET, while maximum biomass yield was obtained at irrigation rates 1.00ET and 1.33ET. This may suggest that the irrigation scheduling program SCHED that has been used is overestimating crop water requirements for obtaining maximum seed yield in the cooler year, while it meets water requirements for maximum biomass yield in both years. In 1992, TDM, which included seeds and plant weight at the above-ground level, increased significantly as the irrigation rate increased up to 1.00ET. There was no significant response when the irrigation rate exceeded 1.00ET (or 1.33ET). The seed yield was significantly increased as the irrigation rate increased to 0.67ET. Total water applied during the 1992 season, which included rainfall, was 9.1 in. at 0.67ET treatment (Table 2). There- fore, an increase in irrigation plus precipitation of over 0.67ET did not produce a significant increase in seed yield. It did, however, increase TDM significantly and delay maturity. In contrast, seed yield results from the 1994 season showed significant differences in yield response among all irrigation treatments (Table 2). Dry matter and seed yields were generally lower in 1994 than in 1992. .

Effect of Irrigation Rates on Water Use EZficiency

Water use efficiency, imgation water use efficiency (IWUE), and harvest index (HI) are summarized in Table 3. The relationships used to describe these functions are:

Table 3. Dry bean water use efiiciency and harvest index as influenced by irrigation amount in the 1992 and 1994 growing seasons.

IWUE ETWUE Harvest*

Year Treatment TDM Seed TDM Seed Index

1992 0.00ET 0.33 ET 0.67 ET 1.00 ET 1.33 ET

1994 0.00 ET 0.33 ET 0.67 ET 1.00 ET 1.33 ET

-- 323 295 308 23 I _-

302 284 282 243

- lblacre per in. - _ _ 696

188 208 247 237 191 264 153 209

_ _ 393 193 266 163 260 185 262 157 226

370 0.53 a 121 0.55 a 199 0.70 b 164 0.59 a 138 0.62 a

193 0.49 a 171 0.58 b 149 0.55 ab 172 0.62 b 146 0.62 b

* Means within columns within year followed by the same letter are not significantly different at alpha = 0.05 as tested by Duncan multiple range test.

ETWUE = (SYi or TDM, - SYd, or TDMd,) f ET

IWUE = (SYi or TDMi - SY* or TDMd,) f Irrig

[ 13

[2]

HI = SY + TDM [31

Where: SYi = irrigated seed yield

TDMi = total irrigated above-ground dry matter SYd, = nonirrigated seed yield

TDMd, = total nonirrigated above-ground dry matter

Irrigation water use efficiency for TDM declined as the irrigation rate increased in 1992, whereas seed yield showed an increase in ETWUE up to 1.00ET. On the other hand, both TDM and seed yield water use efficiencies declined as the irrigation rate increased in 1994 (Table 3). Irrigation use efficiency for TDM was greater than that for seeds at all irrigation rates. In contrast, crop ETWUE decreased considerably for TDM and seeds during both years beyond the 1 .OOET irrigation rate. This may be related to the small yield increase at 1.33ET, compared with lower application rates, and the possibility of deep-water percolation below the root zone. The impact of different irrigation treatments can be expressed in terms of HI. The ratio of seed yield to TDM did not show any significant difference between all treatments for either year, except for the 0.67ET treatment in 1992 and

7

5 6l 1994 yc -.-. i

,:' , * - -* i' ,

i' , ',.

I , /* .'

"10 20 30 40 50 60 70 80 90 100

Days After Emergence

Fig. 1. Dry bean dry matter during 1992 and 1994 growing seasons under different irrigation rates.

J. Prod. Agric., Vol. 12, no. 3, 1999 425

the 0.OOET treatment in 1994. In general, the HI reflects that seed production was higher in 1992 than in 1994. Also, the HI shows that the irrigation treatment has significant impact on the seed:* matter ratio compared with the nonirrigated treatment.

Effect of Irrigation Treatments on Growth Response

In general, irrigation treatments had a significant impact on seed yield and total dry matter in both 1992 and 1994 (Table 2). Plants under limited irrigation (0.33ET), even below the water requirement (16-19 in.; Schwartz et al., 1996), showed a significant increase in dry matter and seed yield, when compared with the nonirrigated treatment (0.OOET) (Table 2). In general, seed yield and dry matter increased as the irrigation rate increased. However, an irrigation rate over 0.67ET did not contribute significantly to the increase of seed yield, where it did for TDM in 1992. The increase in TDM under higher rates of irrigation was consistent during 1992 and 1994 compared with seed yield, where a significant increase was observed only in the 1994 season (Table 2). Treatments O.OOET, 0.33ET, and 0.67ET were harvested 7 d earlier than 1 .OOET, and 10 d earlier than 1.33ET. Therefore, greater irrigation rates may contribute to late maturity and considerable delay in harvest, and hence is a concern, where the possibility of early frost and rainfall exist.

Dry matter response during the growing season as a func- tion of time for different irrigation treatments showed a non- linear relationship (Fig. 1). Total dry matter significantly increased with increasing irrigation amounts (40-90 d after emergence). The impact of the 1.33ET irrigation rate on dry matter production during different times of the growing sea-

son showed a slight improvement in dry matter over l .OOET, especially in the 1994 season. However, dry matter for all treatments showed no significant difference until 40 d after emergence. Furthermore, field observations and plant inspections, where plant root samples from different irrigation treatments were dug out and inspected, revealed a shallower root system under greater irrigation rates, compared with limited or no irrigation.

Effect of Irrigation Rates on Soil Moisture Extraction

The depth of soil moisture extraction by the plant root system is directly related to the water availability in the soil profile. The soil moisture profile showed considerable differences among the irrigation treatments in both years (Fig. 2). Dryland and limited irrigation treatments (0.OOET and 0.33ET) showed deeper soil moisture depletion at harvest than the other treatments down to 24 in., compared with the high rates of irrigation. This may be attributed to a deeper root system that developed under dryland and limited irrigation treatments. Figure 2 shows no soil moisture change below 12 in. for the soil profile under the 1.00ET and 1.33ET treatments compared with lower irrigation rates. In contrast, soil moisture content showed little change below 24 in. for the 0.33ET and 0.67ET treatments. Therefore, under dryland conditions, dry bean has the potential to extract moisture from the soil profile as deep as 24 in. as indicated by Schwartz et al. (1996), that the active rooting depth for the dry bean is between 24 to 36 in., where the majority of moisture is extracted from the top 18 in. It was also reported that roots developed to 30 to 36 in. extract water late in the season when the bean plant is nearly mature (Schwartz et al., 1996). Nielsen and Nelson (1998) found

Soil water content (inchfi)

I

SD(0.05

0.50

0.40

0.20

0.20

0.20

2 3 4 I I I

0 1 2 3 4 I I I I

LSD(0.05)

0.50

0.54

0.1 1

0.06

0.10

1994

Fig. 2. Soil water content characteristic profde under different irrigation treatments at harvest of dry bean in 1992,and 1994 growing seasons.

426 J. Prod. Agric., Vol. 12, no. 3,1999

much deeper water extraction with black bean (6 ft) whenevaporative demand was high and water supply was limited.The soil moisture profile under the over-irrigation treatmentwas almost at field capacity (4.5 in./ft) for 24 to 48 in. soildepths. This means any extra water, such as irrigation orprecipitation, after the crop season, will have the potentialfor deep percolation, and consequently, could lead to. nitrateand other soluble salts leaching to the groundwater.

CONCLUSIONS

Water use by dry bean under variable irrigation rates wasaffected by the water application rate. Optimum irrigationrates and weather conditions during 1992 led to higher seedyield and dry matter. Irrigation rates in both years had a sig-nificant impact on seed yield and TDM. Maximum seedyield was achieved at an irrigation rate equal to 0.67ET inthe cooler year, while 1 .OOET or greater rate was required toobtain maximum biomass yield in both years. Crop ETWUEand IWUE decreased considerably for TDM and seed yieldduring both years beyond the l.OOET irrigation rate.However, both IWUE and ETWUE for dry matter wasgreater than those for seed yield for all irrigation rates.Variable irrigation rates showed a significant effect on theHI (seed:dry matter ratio) compared with dryland treat-ments. Observations of the plant roots confirmed that a shal-lower root system was developed under high irrigation rates,compared with dry and limited irrigation treatments. Thesoil moisture extraction by the roots appeared to be primar-ily at the top 12 in. of the soil profile for high irrigation ratetreatments, compared with 24 in. under dry and limited irri-gation treatments, especially in 1992. The soil moisture pro-file was at or near field capacity under the over-irrigatedtreatments (1.33ET) after harvest, which could lead to thepotential of deep water percolation and leaching of nitrateand other soluble salts.

ACKNOWLEDGMENTS

The authors would like to thank Brian Leib and DavidSanford for their help during the course of the study.


published april 19, 2013 dry beans · 2017. 3. 21. · 0.33, 0.67, 1.00, and 1.33 of estimated...

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