Grain Sorghum Response to Row Spacings and Seeding Rates in Kansas

Previous research suggests that reducing row spacings increased grain sorghum's [Sorghum bicolor (L.) Moench.] yield potential. However, most of this research was conducted in environments with lower yield potentials than currently found in northeast Kansas. The objectives of this study were to determine the impact that reducing row spacing had on grain sorghum grain yields and yield components. Research was conducted over five location-years in northeast Kansas to evaluate the effects of row spacings and plant populations on grain sorghum yields. Two hybrids were planted in 10, 20, and 30 in. rows at 30 000,60 000, and 90 000 plants/acre. In environments where yields exceeded 100 bu/acre, yields were approximately 10% higher from the 10 and 20 in. rows than from the 30 in. rows. When moisture and temperature stress limited grain yields, no yield differences occurred among the row-spacing treatments. Grain yields responded little to changes in plant populations throughout the study. Reducing spacing per plant (reducing row spacing or plant populations) reduced panicles per plant. Caryopses per panicle and caryopses weights were affected primarily by growing conditions during their respective development periods. These results suggest that decreasing sorghum row spacing below 30 in. will increase grain yields under high yielding environments with little risk of reducing yields in lower yielding environments. This study also indicates that seeding rates do not have to be altered as narrow row systems are adopted. Research QuestionPrevious research has shown an increase in grain yields in crops such as soybeans and corn when row spacing was reduced. This response has varied across environments based on their yield potential. Grain sorghum producers are beginning to question the impact that reducing row spacings from 30 or 36 in. to 10 or 20 in. will have on grain yields. A secondary concern is whether plant populations have to be increased simultaneously to achieve maximum grain yields. The objective of this study was to determine the impact that row spacings and plant populations have on grain sorghum yields. Literature SummaryRecently, the influences of row spacing on grain sorghum canopy architecture, light interception, and grain yields have been of interest. Several researchers have reported higher yields in narrow rows (12, 15, and 20 in.) under favorable growing conditions. The advantage of the narrow rows has been attributed to improved light and water use efficiency. Others have reported stable grain sorghum yields over a wide range of plant populations within a given environment, suggesting that as sorghum row spacings are reduced, optimal yields may be achieved without increasing plant populations. Study DescriptionField studies were conducted during 1995 and 1996 at three locations in northeast Kansas. Early- and late-maturing grain sorghum hybrids were seeded in 10, 20, and 30 in. rows at seeding rates designed to achieve target plant populations of 30 000, 60 000, and 90 000 plants/acre. The final average stands were 36 654, 59 904, and 86 967 plants/acre. Applied QuestionsDid row spacings affect sorghum grain yields? The effects of reducing row spacings from 30 in. to 20 or 10 in. were different in high- and low-yielding environments. In the environments with grain yields above 100 bu/acre, narrow rows resulted in higher yields than the wide rows (Fig. 1). The 10 in. rows resulted in grain yields that were approximately 9% (11 bu/acre) greater than those in the 20 in. rows and 11% (15 bu/acre) greater than those in the 30 in. rows across all environments. In environments where grain yields were under 100 bu/acre, no yield differences occurred among the row spacing treatments. Fig. 1Grain sorghum yields at three row spacings in five location-years in northeast Kansas. The advantage of the narrow rows in the higher-yielding environments was probably the result of greater light and water use efficiency. In the lower-yielding environments, the lack of yield response across the row spacing treatments was probably the result of their water use characteristics. When an extended period of dry weather occurred, the narrow rows depleted the stored soil water faster than wide rows, in which the canopy had not closed. Under such conditions, increased light interception by the narrow rows increased water use. Because the dry period extended for several weeks, the narrow rows probably used more water, experienced water stress earlier than the wide rows, and suffered water stress for a longer time. Did plant populations have to be increased to achieve maximum yields as row spacings were reduced? Regardless of the row spacing, grain sorghum yields increased as plant populations were increased from 30 000 to 60 000/acre. However, no further increase in grain yields occurred as populations increased to 90 000 plants/acre. These results are similar to those of previous research, which indicated that sorghum yields were very stable across a wide range of plant populations. This stability was the result of the plant's ability to adjust panicle number per plant and seed number per panicle in response to the conditions encountered during the growing season.