Search

Many coarse‐textured surface soils in the southeastern Coastal Plain are prone to develop tillage pans which restrict root proliferation and moisture utilization in subsoils. The effect of tillage treatments on soybean [Glycine max(L.) Merr.] growth and soil moisture utilization was investigated on Norfolk sandy loam (Typic Paleudult) and Wagram loamy sand (Arenic Paleudult) soils. The three tillage treatments used were: conventional moldboard plowing and disking only before planting; or plowing and asking, followed by either chisel‐plowing; or subsoiling with bedding before planting. Measurements were made of top and root dry weight, leaf area, grain yield, soil water content and soil moisture tension. Breaking the tillage pan by chisel‐plowing or subsoiling increased top growth and leaf area of soybeans at full bloom. The percentage of roots below 30 cm was increased by subsoiling and chisel‐plowing when rainfall was below normal during the growth period. A higher proportion of roots was in the top 10 cm of soil with conventional tillage than with chisel‐plowing or subsoiling. Chisel‐plowing and subsoiling increased the amount of soil moisture utilized below a depth of 30 cm. Grain yields were increased by chisel‐plowing or subsoiling in those years when rainfall was below normal during lateflowering and the beginning of pod development. Subsoiling or chisel‐plowing of soils with compacted pans will increase soybean yields during years in which below‐average precipitation occurs during late‐flowering and the beginning of pod set. Yield increases are attributed to increased root proliferation below the pan and greater utilization of subsoil moisture.

Several droughts during the past decade in humid regions of the USA, especially the Southeast, have intensified the interest in supplemental irrigation. One objective of this study was to evaluate the effect of supplemental irrigation in a humid environment on corn (Zea maysL.) production on an Atlantic Coastal Plain soil having a tillage pan. A second objective was to evaluate two alternative techniques for scheduling supplemental irrigation in humid regions. The study, conducted on a Wagram soil (Arenic Paleudults)‐Norfolk soil (Typic Paleudults) from 1979 to 1981, employed a split plot design with water level (irrigation scheduling) as the main block. Water levels were control or dryland (W1), scheduled irrigation water applications based on a computerized water balance model (W2), and scheduled water applications based on tensiometer measurements (W3). Subplot treatments were time of N application in 1979 and 1980 and cultivation intensity in 1981. Compared with a normal rainfall of 447 mm during the growing season, 464, 262, and 220 mm fell during 1979, 1980, and 1981, respectively. The average amount of irrigation water applied over the 3‐yr period based on the water balance model was 40 mm greater than the 3‐yr average of 179 mm applied based on the tensiometers. Grain yield as affected by subplot treatment was not significantly different for any year. Mean grain yields for the 3‐yr period were 2.58, 7.73, and 8.14 Mg ha−1, for treatments W1, W2, and W3, respectively. Either irrigation scheduling method offers large yield improvements in drier years, but no significant yield difference occurred for the two scheduling techniques. In the wetter year 1979, irrigation increased yield by 2.45 Mg ha−1, whereas in the dryer years of 1980 and 1981 the increases were 6.53 and 7.06 Mg ha‐1, respectively.

Field studies were conducted during a 4‐year period to determine “Vernal“ alfalfa (Medicago satvaL.) dry matter yield in response to irrigation and fertilization variables. In the Northern Great Plants alfalfa forage production contributes significantly to overall agricultural land use; consequently optimization of resources use is desirable. Limited available information has created a need for such research. This study was carried out on a Maddock sandy loam soil, a member of the sandy, mixed frigid Udorthentic Haploboralls. Four irrigation levels, ranging from dryland to excessive irrigation, were established as whole plots in a randomized block, split plot design. Eight different fertilizer treatments of P, K, and S were applied to split plots during the 1st year of the study. Under a three harvest per season management system dry matter yield was significantly affected by harvest number and irrigation treatment each year. Within the dryland and deficient irrigation treatment by year, yields decreased with each cutting; with optimum and excessive irrigation, yields varied inconstantly with cutting; yields increased 14 to 330% over dryland by increasing irrigation applications. Total seasonal crop water use, or evapotranspiration (ET), was determined using a water balance approach. Drainage (DRAIN) was calculated, using flux gradients calculated from tensiometer data, and appropriate soil properties. Other inputs, including irrigation (IRR), growing season precipitation (PPT), and soil water depletion (DEPL), were measured. In addition, water use efficiency (WUE) was calculated by treatment by year. Multiple linear regression analyses were used to relate actual dry matter yield (YIELD) and relative yield (RELY) to several independent variables. When plant water stress existed throughout the growing season, RELY correlated with relative evapotranspiration (RELET) in a near perfect, linear manner. Under nonstress conditions IRR, PPT, and DEPL required consideration to attain nearly perfect correlation of RELY with RELET. The results of this study indicate that under plant water stress conditions, alfalfa dry matter yield is a linear function of plant water use.

Increased availability of water for supplemental irrigation in the upper Midwest has enhanced an interest in growing soybeans [Glycine max(L.) Merr.] on moderately coarse‐textured soils where they have not previously been introduced. The objectives of this study were to determine the yield potential of supplementally irrigated soybeans on these soils and to develop an irrigation schedule for efficient water management. The study, conducted on Maddock sandy loam from 1972 to 1974, employed a splitsplit plot design with water level as the main block and N fertility rates (0, 56, 112, and 224 kg/ha) as sub‐plots. Water levels were Wl (dryland), W2 (under‐irrigation), W3 (optimum) and W4 (over‐irrigation). Sub‐sub plots were planting dates in 1972 and cultivars in 1973 and 1974. Soil samples were collected from 15 to 30 cm intervals to depths of 90, 150, or 270 cm throughout the study and analyzed for NO3‐N in the soil profile under irrigated conditions. Grain yields were significantly different for water levels during each of the 3 years. Threeyear yield means were 543, 1,823, 2,428, and 2,164 kg/ha for Wl, W2, W3 and W4, respectively. The application of 24 kg/ha N fertilizer in 1972 increased grain yield at the 0.95 probability level. The seed was not inoculated that year but was inoculated in 1973 and 1974. Soybeans planted 10 May 1972, outyielded soybeans planted 6 June by 356 kg/ha. ‘Anoka’ outyielded the ‘SRF‐100’ cultivar by 137 kg/ha in both 1973 and 1974. An irrigation schedule based upon tensiometers placed at the 30 cm depth until 15 July (growth stage R2) and at the 45 cm depth after 15 July proved effective in applying irrigation water. Analysis of NO3‐N in the soil profile at different dates during the 3‐year period showed that under heavy fertilizer NO3‐N applications, the NO3‐N moved below the crop rooting zone when excess water was applied. Based upon results of this study, soybeans can be seriously considered as a crop to be included in cropping systems for irrigated, moderately coarse‐textured soils in the Upper Midwest.

Irrigation in humid regions is often delayed based on forecasted rainfall or due to labor shortages or equipment problems. The effects of tillage and delayed irrigation on corn (Zea maysL.) were investigated in 1982 and 1983 on a Norfolk loamy sand (Typic Paleudult) with a tillage pan. Irrigation treatments were: optimum irrigation when tensiometer measured soil water pressure at the 25‐ or 30‐cm depth was −40kPa; 2‐day and 4‐day delays after irrigation was needed; and a nonirrigated control. Each irrigation treatment was superimposed on land prepared by two tillage treatments: (i) conventional and (ii) subsoiling and bedding. Delayed irrigation during a wet growing season (1982) had little effect on corn growth. Delayed irrigation during the dry growing season (1983) reduced plant height, leaf area, biomass, and grain yield on conventionally tilled soil but only grain yield on subsoiled plots. With a 4‐day irrigation delay, grain yields were reduced 29% below the 10.22 Mg ha−1yield for conventional tillage but only 11% below the maximum of 10.56 Mg ha−1for subsoiling. Irrigation in 1982 increased mean grain yield of all three delay treatments by 23 and 1% for conventionally tilled and subsoiled treatments, respectively. In 1983, these increases were 314 and 18%, respectively. A 1‐yr subsoiling carryover (1983) resulted in a yield of 8.89 Mg ha−1vs. a current‐year subsoiled yield of 10.68 Mg ha−1. A 2‐yr carryover (1982) resulted in a yield of 9.60 vs. 10.60 Mg ha−1from current year subsoiling.

An increase in the access to irrigation water in the Northern Great Plains is effecting large increases in the acreages of soils being irrigated. Much of this water is being applied to medium to coarse‐textured soils which hold a maximum of 7 to 12 cm of available water in a 152 cm deep profile. An investigation was conducted in the field to devise a system, using tensiometers, to schedule the application of irrigation water to sugarbeets growing on these soils. Tensiometers were installed at various soil depths, and irrigation water was applied with a small plot irrigator when soil moisture tension reached a predetermined level. One tensiometer located at the 45 cm depth was equally effective in scheduling as two tensiometers, one positioned at a depth of 30 and one at 61 cm. Maximum crude sugar yields of 8.4 to 8.8 metric tons/ha were obtained in 1971 and 1973, respectively. Total water use efficiency was 0.15 to 0.16 metric tons of crude sugar/ha per cm. The maximum irrigation water use efficiencies were 0.32 and 0.36 for 1971 and 1973, respectively. It is concluded that 56 to 62 cm of water, well distributed throughout the growing season, is sufficient for sugarbeet production is southeastern North Dakota in a year of normal growing season temperatures.