Row Spacing and
Direction Effects on Yield, Water Use, Tillering and
Light Interception of One-Irrigation Barley
The one-irrigation barley variety Solum is adapted to wide row spacing, and sometimes yields higher in wide compared to narrow spacing. This study was initiated to determine the effect of row spacing and direction on Solum water use and yield components. Solum barley was planted at the Marana Agricultural Center at 6, 12, 18, and 24 inch row spacings in north-south and east-west rows in late November and late-February or early March over 2 growing seasons. Row spacing and direction had little effect on yield and yield components, water use, tillering, and light interception. Nevertheless, in some instances narrow row spacing resulted in more heads that were smaller and had lighter kernels than wide row spacing. We measured greater soil water depletion for the narrow row spacings at the late planting date one year due to greater stem density. The narrow rows intercepted more light than wide rows and the wide rows intercepted more light at solar noon in east-west compared to north-south rows. We were not able to confirm the theory that soil water is conserved in wide rows for use at more critical stages later in the season.
One-irrigation barley is able to grow and produce relatively plump kernels with a single irrigation near planting. Seco and Solum are one-irrigation barley varieties that have been released in the past 10 years. Previous work has shown that one-irrigation barley performs well in row spacings of 12 to 18 inches (Ottman et al., 1988). One-irrigation barley varieties perform well in wide rows because they are tall and produce many tillers. Also, it has been suggested that soil moisture depletion is delayed in wide rows and moisture is conserved for more critical stages later in the season. Row direction and planting date provide an additional complication to row spacing. For example, in rows running east-west and planting early, direct sunlight does not reach the soil surface for much of the season because of the oblique angle of the sun in the winter.
The purpose of this study is to determine the effect of row spacing and direction on one-irrigation barley water use and yield components.
Experiments were conducted at the Marana Agricultural Center on a Pima clay loam soil. The one-irrigation barley variety Solum was seeded with a single row planter at a rate of 10 seeds per square foot, or about 44 pounds of seed per acre. The seed was planted at 4 row spacings (6, 12, 18, and 24 inches), 2 row directions (north-south and east-west), two planting dates (early and late), and two growing seasons (1991 and 1992). The planting dates for the 1991 growing season were 20 Nov 90 and 20 Feb 91 and the planting dates for the 1992 growing season were 20 Nov 91 and 03 Mar 92. Fertilizer was applied preplant at a rate of 92 lbs N/A and 60 lbs P2O5/A as urea and 11-52-0 (1991) or 18-46-0 (1992). A single border flood irrigation was applied at these planting dates and the plots received no more irrigation after planting. Effective rainfall for the various planting dates was: 6.60 inches (20 Nov 90), 1.55 inches (20 Feb 91), 9.53 inches (20 Nov 91), and 7.52 inches (03 Mar 92). The experimental design was a randomized complete block with 8 treatments (4 row spacing and 2 row directions) and 4 replications. The plots were 10 ft by 10 ft in size.
Soil moisture depletion, stem number, and light interception were measured on a weekly basis. A neutron probe access tube was installed in each plot within the rows in 1991 and both within and between rows in 1992. Soil moisture depletion was calculated from neutron probe readings in 1 ft increments to 5 ft. Stem number was calculated from an area 2 ft wide and 2 ft long except for the 18 inch row spacing where the width of the area was 1.5 ft. Light interception was measured within an hour of solar noon using a sunfleck ceptometer with a sensing surface of 7/16 inch by 34.5 inches placed at the soil surface. Plants were harvested from the same area stem counts were measured. The following was determined at harvest: total biomass, grain yield, heads per square foot, kernels per head (by calculation), kernel weight, and harvest index.
Results and Discussion
Row spacing and direction had little effect on yield and yield components Tables 1a - 1d. Total plant yield was highest at the narrow row spacing for the 20 Feb 91 planting date but not the other planting dates. Grain yield was not affected by row spacing or direction at any planting date. Nevertheless, relative yields averaged over the row spacing was 105% (6 inch), 99% (12 inch), 100% (18 inch) and 96% (24 inch) and relative yields averaged over the row directions were 100.3% (north-south) and 99.7% (east-west). The narrow row spacings had more heads than wider spacings in some cases, but the heads were smaller and the kernels lighter. Harvest index was not affected by row spacing or direction.
We were not able to measure any effects of row spacing and direction on soil moisture depletion during the 1992 growing season, but some interesting effects were measured during the 1991 growing season Tables 2a - 2d. A row spacing by direction interaction was measured during the early part of grain fill for the 20 November 90 planting date where narrow rows used less water than wider rows in a north-south row direction, but more water in a east-west row direction. At the 20 Feb 91 planting date, a row spacing by direction interaction was also detected but in an opposite trend to the earlier planting date. At the 20 Feb 91 planting date, we also measured greater soil water depletion for narrow compared to wide rows.
Stem density was not affected by row spacing or direction except for the 20 Feb 91 planting date where narrow rows had higher stem density than wide rows Tables 3a - 3d. Stem density can account for the differences in water use observed at this planting date mentioned in the paragraph above.
The narrow rows intercepted more light than the wide rows as expected Tables 4a - 4d. The wide rows intercepted more light at solar noon in east-west rows than north-south rows.
The one-irrigation barley variety Solum is adapted to a wide range of row spacings. The yield advantage of row spacings of 12 to 18 inches measured in previous studies was not obtained in this one. The pattern of water use, tillering, and light interception were somewhat similar, except in a few instances, regardless of row spacing since Solum tillers well and covers the soil surface despite wide rows or low initial stand.
The technical assistance of Dave Parsons is greatly appreciated.
This is a part of publication
AZ1059: "1998 Forage and
Grain Agriculture Report," College of Agriculture,
The University of Arizona, Tucson, Arizona, 85721.