Response of Hard Red Winter Wheat to Seed Density and Seeding Rate in No‐Till

Defining the optimum seeding rate for wheat ( Triticum aestivum L.) is complex because this crop has the capacity to create and abort tillers in response to environmental conditions. Several soil physical characteristics affecting germination and emergence are altered with the change from conventional tillage (CT) to no‐till (NT), and these may influence final stand. The objective of this study was to determine whether either seed density or seeding rate influenced the performance of hard red winter wheat (HRWW) in a rainfed wheat‐fallow rotation under NT. Experiments were conducted during four growing seasons on a Keith silt loam soil (fine silty, mixed, mesic Aridic Argiustoll) in northwestern Kansas. The experimental design was a randomized complete block with four replications. Experimental variables were seed density and seeding rate in a complete factorial arrangement with four levels of seed density and three of seeding rate for a total of 12 treatments. Seed weights ranging from 27 to 35 g/1000 kernels (58–63 Ib/bu) were obtained from bin‐run, foundation‐grade, ‘Newton’ seed selectively processed in multiple runs over a gravity table. This process separates seed on the basis of seed density (mass per unit volume), which is then converted into thousand‐kernel and test weights. Hence, these units of mea‐ sure were used in this report. Seeding rates were 450 000, 600 000, and 750 000 viable seeds/acre. Seeding was done with a shop‐fabricated drill that allowed seed placement as deep as necessary to reach moisture, while maintaining a constant covering depth of 1.5 in. Heavier seed produced greater numbers of seedlings per unit area and a higher emergence percentage than light seed, but seed density had little effect on the final number of spikes per unit area, ratio of spikes per plant, or kernels per head. Increasing seeding rate resulted in more seedlings and spikes per unit area but decreasing numbers of kernels per head. Overall, responses were compensating, so that grain yield was unaffected by either seed density or seeding rate. Although test weight, protein concentration, and thousand‐kernel weight were influenced positively by seeding rate and seed quality, the responses were small and probably of little practical value. Results suggest that the HRWW plant can adapt as effectively under NT as has been reported for CT. Because future emergence conditions are unknown, large heavy seed still should be preferred over small light seed, particularly if seed costs are the same or the latter has been in storage for more than one season. Research Question Defining the optimum seeding rate for wheat is complex because this crop has the capacity to create and abort tillers in response to environmental conditions. With the current movement toward cropping systems with little or no tillage, a need exists to reexamine seed quality and seeding rate as they affect wheat production under no‐till conditions. The objective of this research was to determine whether either seed density or seeding rate influenced the productivity of hard red winter wheat (HRWW) in a rainfed wheat‐fallow rotation under no‐till. Literature Summary Changing from conventional tillage to no‐till has been shown to alter several soil physical characteristics that affect seed germination, seedling emergence, and growth of the wheat plant. Thus, recommendations on seed quality and seeding rate developed from systems under conventional tillage may have to be modified. With good to excellent seeding conditions under conventional tillage, seedlings originating from small seed have been shown to emerge as well as those from large seed, and seed size or density had little effect on grain yield. The advantage of large, heavy seeds over small, light ones generally increased as seeding conditions worsened. The semiarid Central High Plains is noted for precipitation deficits, and no‐till has value for conserving moisture. However, much of the research on seed density has been done in higher rainfall areas where the benefits of water conservation with no‐till are less important. Study Description Experiments were conducted during four growing seasons on a Keith silt loam soil in northwestern Kansas. New sites were used each season, but all had been in no‐till for a minimum of 10 yr. Sites were fertilized according to Kansas recommendations based on soil tests. The experimental design was a randomized complete block with four replications. Treatments consisted of all combinations of four seed densities (including bin‐run) and three seeding rates. Seed densities ranging from 26.8 to 35.4 g/1000 kernels (57.8 to 63.6 lb/bu) were obtained from bin‐run, foundation‐grade, cv Newton seed selectively processed in multiple runs over a gravity table. Seeding rates were 450 000, 600 000, and 750 000 viable seeds/acre. Seeding was done with a shop‐fabricated no‐till plot drill that could place seed as deep as necessary to reach moisture, while maintaining a constant covering depth of 1.5 in. Plot size was five 12‐in. rows wide and 35 ft long. Applied Questions Does either seed density or seeding rate affect HRWW seedling emergence and plant development? Heavier seed produced greater numbers of seedlings per unit area and a higher emergence percentage than light seed, but seed density had little effect on the final number of spikes per unit area, ratio of spikes per plant, or kernels per head (Table ). Increasing seeding rate resulted in increasing numbers of seedlings and spikes per unit area. However, these were offset by decreasing numbers of kernels per head. Given that seeding rate and seed density had an impact on seedling emergence and plant development, did these affect yield? Overall, responses were compensating so that grain yield was unaffected by either seed density or seeding rate (Table ). One can conclude from this that the HRWW plant can adjust to sizeable differences in plant population in no‐till to produce yields constrained mostly by other agronomic inputs and the season's climatic features. If seed density or seeding rate have no general affect on yield, why not buy the least expensive, unconditioned seed and seed at a low rate? We mostly condition wheat seed to remove debris, weed seeds, and cracked or small, shriveled kernels rather than to obtain larger, heavier seeds. The process often can be justified on those practical reasons alone. However, medium to heavy seed always produced more seedlings than did light seed and, in one season with the lowest percentage emergence seedling (73%), heavy seed produced more seedlings than did the medium seed. Quickly establishing a uniform and complete stand should always be an early goal in getting the crop off to a good start. Light seed and low seeding rates did not appear to contribute to such a goal. Because future emergence conditions are unknown, large heavy seed should still be preferred over small light seed, particularly if seed costs are the same or the latter has been in storage for more than one season. Can adjustments in seeding rate and seed quality increase or decrease the amount of crop residue? Data on crop residue were collected only for two seasons on above ground biomass. Crop residue averaged 2.53 tons/acre, and the ratio of residue to grain averaged 1.65 lb/lb, but neither appeared to be influenced by either seeding rate or seed density. Averages for selected growth and yield characteristics of HRWW as influenced by seeding rate and seed density. Treatment Seed density Seeding rate Emerged seedlings Spikes Spike ratio Grain yield Head fill 1000/ 1000/ % million/ spikes/ bu/ kernels acre acre acre plant acre /head Bin run ‐‐ 473a 79a 2.201a 4.78a 46.3a 23.5a Light ‐‐ 432b 72b 2.132a 5.15a 43.6b 22.8a Medium ‐‐ 472a 79a 2.177a 4.78a 45.7ab 23.2a Heavy ‐‐ 485a 81a 2.264a 4.85a 46.1a 22.4a <jats:tr