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Irrigation management practices for corn production in north central Kansas.

In Kansas, surface water and groundwater shortages plus increasing demands for water by urban and recreational interests have led to drastic declines in the amount of water available for irrigation. In the Bostwick Irrigation District of north-central Kansas, water allocations were reduced from the normal 38.1 ha-cm (15 acre-in) of water to 17.8 ha-cm (7 acre-in) in 1991. When producers change from a fully irrigated situation with few restrictions to a system in which water is limited either by well capacity or by allocation, they need reliable information on scheduling techniques and yield response to irrigation water inputs.

The main objective of irrigation scheduling is to manage irrigations for greatest effectiveness. Water must be applied frequently enough to avoid plant water stress and in amounts adequate to recharge the plant rooting zone. Inadequate irrigation results in crop stress and crop yield loss. With only a limited amount of irrigation water available, timing of application becomes critical.

Corn grain yields are most sensitive to water stress during the reproductive [TABULAR DATA FOR TABLE 1 OMITTED] [TABULAR DATA FOR TABLE 2 OMITTED] phase of development. Several studies (Classen and Shaw; Denmead and Shaw; Frey) have reported that greatest yield reductions from water stress occurred during a period starting just prior to silking and continuing for 1 to 2 weeks after silking. Shaw reported that the most critical period for drought stress is from 5 days before to 5 days after silking, followed by a 30-day period that is less critical. Eck found that kernel numbers were not affected by water deficits during early grain fill, unless severe deficits were imposed early in the period. Harder et al. reported that water stress occurring within 2 weeks after silking reduced the number of kernels per plant by 15%. Additional stress cycles had little effect on kernel number. In general, greatest reductions in kernel numbers result from stress during silking and very early grain fill stages.

The objectives of this research were to examine water use of corn, and develop irrigation management strategies that ensure adequate soil water conditions exist during the most critical period in crop development, thus maximizing grain yield with minimum irrigation water inputs.

Materials and methods

The study was conducted on the irrigation experiment field located in the Bostwick Irrigation District, near Scandia, Kansas.

The soil is a Crete silt loam. The Crete series consists of deep soils that have a loamy surface underlaid by a dense, slowly permeable montmorillonitic subsoil (B21t, B22t) extending from 38 to 76 cm (15 to 30 in) in depth. The subsoils are very hard when dry and very firm when moist (Atchinson and Gier). On-site determinations of permanent wilting point and field capacity showed that the soil holds about 17.3 cm (6.8 in) of available water in the top 90 cm (3 ft).

Plot description and cultural practices are given in Table 1. The experimental design was a randomized complete block, replicated four times.

In 1975-1977, treatments consisted of (1) irrigations at the 10-leaf stage, tassel emergence, 1 week after tasseling, and 2 weeks after tasseling; (2) irrigations at tassel emergence, 1 week after tasseling, and 2 weeks after tasseling; (3) irrigations 1 week after tasseling and 2 weeks after tasseling; (4) irrigation 2 weeks after tasseling; and (5 and 6) irrigation when 40% (treatment 5) or 60% (treatment 6) of the available water in the top 90 cm of the soil profile was depleted. In 1978-1980, irrigation treatments were (1) irrigation at tassel emergence; (2) irrigations at tasseling and 1 week after tasseling; (3) irrigations at tasseling, 1 week after tasseling, and 2 weeks after tasseling; and (4 and 5) irrigation when 40% (treatment 4) or 60% (treatment 5) of the available soil water in the top 90 cm of the soil profile was depleted. In 1981-1991, treatments were (1) no irrigation; (2) irrigation at tassel emergence; (3) irrigations at tasseling and 1 week after tasseling; (4) irrigations at tasseling, 1 week after tasseling, and 2 weeks after tasseling; and (5) irrigation when 50% of the available water in the top 90 cm of soil was depleted (19811983) or when 65% of the available soil water in the top 45 cm (18 in) was depleted (1984-1991). Tasseling was selected as the starting paint for irrigations because it is a good visual indicator of the critical reproductive phase of corn development. Starting irrigations at tassel emergence ensures that the soil will be moist at silking.

Neutron attenuation measurements were taken from one access tube placed in the third row of each plot. Readings were [TABULAR DATA FOR TABLE 3 OMITTED] at each 15 cm (6 in) depth increment from 15 cm through 90 cm. Neutron attenuation measurements were taken to a depth of 152 cm (5 ft) in 1991 and 1992. Readings were taken at about 1-week intervals. In 1975-1977, irrigation water was applied to plots through siphon tubes from an open ditch. Ten cm (4 in.) of water were applied per irrigation. In 1978-1991, water was metered on plots through gated pipe and 7.6 cm (3 in) of water were applied at each irrigation. Duration of irrigation was 24 hours. Growing season rainfall for the years 19751991 is given in Figure 1.

Apparent irrigation water-use efficiency (AIWUE) was calculated by the following formula:

AIWUE = (Yirr-Ydry)/Wirr

where Yirr and Ydry are the grain yields (Mg [ha.sup-1]) of irrigated and dryland treatments, respectively, and Wirr is the amount (mm) of irrigation water applied (Cassel and Edwards). The number of irrigations in the soil water depletion treatment (1981-1991) averaged three with a range of one to five.

The evapotranspiration (ET) curve was developed using measured ET values from periods when rainfall was less than 6.4 mm (0.25 in) and no irrigation was applied and plotted against fraction of thermal units as a normalized time scale. Measured ET rate was calculated as the sum of soil water depletion plus rainfall divided by the number of days in the measurement interval (mean

= 7.8 days). Fraction of thermal units (FTU) is defined as thermal units accumulated from emergence to the time in question, divided by the total thermal units accumulated from emergence to physiological maturity (Amos et al.).

Grain yields were determined by machine harvesting the center two rows of each six-row plot. Yields were adjusted to a water content of 155 g [kg.sup.-1] (15.5%) on a wet mass basis.

Results and discussion

From 1975-1977 yields in plots that were irrigated four times (10-leaf stage, tasseling, 1 week after tasseling, and 2 weeks after tasseling) were not different than those plots that were irrigated three times beginning at tasseling (Table 2). Delaying irrigation until 1 week after tasseling reduced yields by 24% compared to irrigating three times beginning at tasseling. [TABULAR DATA FOR TABLE 4 OMITTED] Delaying irrigation until 2 weeks after tasseling further reduced grain yields. Irrigating when 40% of the available water in the top 90 cm of soil was depleted did not significantly improve yield over that achieved by irrigating three times beginning at tasseling. Over the 3-year period, the 40% soil water depletion treatment required an average of five irrigations.

From 1978-1980 one irrigation at tasseling produced 91% of maximum yield (Table 3). Two irrigations (tasseling and 1 week after tasseling) produced yields that were not significantly different from those achieved by irrigating at the 40% soil-water depletion level. Waiting until 60% of the available soil water was depleted re-suited in the lowest yields in the test.

During the period 1981-1991, one irrigation at tasseling produced 82% of maximum yield (Table 4). Values ranged from 61% of maximum yield in 1983 to 96% in 1981. Greatest apparent irrigation water-use efficiency was achieved with one irrigation, and efficiency declined as the number of irrigations increased [ILLUSTRATION FOR FIGURE 2 OMITTED]. When averaged over the 11-year period, two irrigations (tasseling and 1 week after tasseling) produced 94% of maximum yield. Values ranged from 79% of maximum yield in 1983 to 99% in 1981. In 7 of the 11 years, 2 irrigations produced at least 90% of maximum yield. In only 2 years (1983 and 1987) did the three-irrigation treatment (tasseling, 1 week after tasseling, and 2 weeks after tasseling) yield significantly less than the soil-water depletion treatment. When averaged over the 11-year period, scheduling irrigation by planned soil-water depletion did not improve yields over irrigating three times beginning at tasseling. When irrigations are timed to coincide with periods of high crop water use, acceptable yields can be achieved with a limited amount of irrigation water.

The three-irrigation treatment (irrigation at tasseling, 1 week after tasseling, and 2 weeks after tasseling) was present in all years of the experiment (Tables 2, 3, and 4). Yields in this treatment increased from a mean of 8.2 Mg [ha.sup.-1] (130 bu/ac) in 1975-1978 to 10.6 Mg [ha.sup.-1] (170 bu/ac) in 1984-1991. This was not due to a change in irrigation management but to genetic improvement in corn hybrids. Data from corn hybrid performance testing done on the Irrigation Experiment Field are given in Figure 3. Test means of all entries are plotted against year of the century for the period 1968-1992. From a linear regression analysis, yields have increased at an annual rate of about 0.19 Mg [ha.sup.-1] (3 bu/ac).

Soil water depletion rates from irrigation and rainfall-free time periods are given in Figure 4. Time periods were selected to illustrate water depletion rates when crop root development had reached maximum volume. The bulk of water depletion was from the top 60 cm (2 ft) of soil. Data from 1991 and 1992 (in 1992 the experiment was not irrigated and values shown represent an average of the no irrigation and 65% soil water depletion treatments) show little water depletion below 90 cm (3 ft). The lack of water depletion below 90 cm indicates minimal root activity at deeper profile depths. In a study conducted on the same Crete soil, Stone et al. also found little water depletion below 90 cm. No difference was observed in depth of soil water depletion between the irrigated and non-irrigated treatments. Consequently, when planning irrigation on this soil, water reserves below 90 cm should not be considered.

From the regression equation, water use rate was above 7 mm/day (0.28 in/day) from about 0.54 to 0.64 FTU [ILLUSTRATION FOR FIGURE 5 OMITTED]. Peak water-use rate, 7.4 mm/day (0.29 in/day), was at 0.59 FTU. Tasseling, silking, and blister kernel occur at 0.44, 0.49, and 0.61 FTU, respectively (mean values from 1984-1991). If only limited amounts of irrigation water are available, application during the peak demand period from silking to blister kernel will reduce losses from water stress. In north-central Kansas, acceptable corn yields can be obtained with one or two irrigations if the irrigations are timed to meet high plant water-use demands associated with critical growth stages.

REFERENCES

Amos, B., L.R. Stone, and L.D. Bark. 1989. Fraction of thermal units as the base for an evapo-transpiration crop coefficient curve for corn. Agron J. 81:713-717.

Atchinson, C.H., and D.A. Gier. 1967. Soil Survey of Republic County, Kansas. Soil Cons. Ser. U.S. Dept. Agr., Salina, KS.

Cassel, D.K., and E.C. Edwards. 1985. Effects of subsoiling and irrigation on corn production. Soil Sci. Soc. Am. J. 49:996-1001.

Classen, M.M., and R.H. Shaw. 1970. Water deficit effects on corn. II Grain components. Agron. J. 62:652-655.

Denmead, O.T., and R.H. Shaw. 1960. The effects of soil moisture stress at different stages of growth and development and yield of corn. Agron. J. 52:272-274.

Eck, H.V. 1986. Effects of water deficits on yield, yield components, and water use efficiency of irrigated corn. Agron. J. 78:1035-1040.

Frey, N.M. i982. Dry matter accumulation in kernels of maize. Crop Sci. 21:118-122.

Harder, H.J., R.E. Carlson, and R.H. Shaw. 1981. Yield, yield components, and nutrient content of corn grain as influenced by post-silking moisture stress. Agron. J. 74:275-278.

Shaw, R.H. 1974. A weighted moisture stress index for corn in Iowa. Iowa State J. Res. 49:101-114.

Stone, L.R., R.J. Raney, E.T. Kanemasu, and W.L. Powers. 1978. Irrigation water movement below the corn root zone in a Crete silt loam. J. Soil Water Cons. 33:294-296.
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Author:Gordon, W.B.; Raney, R.J.; Stone, L.R.
Publication:Journal of Soil and Water Conservation
Date:Jul 1, 1995
Words:2081
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