The Grain Growing Classroom

Fundamentals for Successful Cereal Crop Establishment

by Joel K. Ransom
NDSU Extension Agronomist - Cereal Crops
joel.ransom@ndsu.edu

Plant population is the most basic component of yield. Consequently, the successful establishment of adequate crop plant density is a key step in achieving profitable crop production.  Here are a number of fundamental factors that can influence wheat and corn stands.

Seeding rate for wheat: One size doesn’t fit all
The trend in recent years has been towards higher seeding rates in most crops. This practice has led to significant gains in yield potential in crops like soybeans and corn in some areas of the country.  Furthermore, in the past, seed was considered a relatively cheap input, so planting extra seed was viewed as a relatively inexpensive way of ensuring a good stand.  That may not be the case today. The following points summarize the most recent recommendations relative to seeding rates in small grains.

Varieties and seed lots within a variety can vary considerably in the weight of the kernels and the germination percentage. (Table 1). When determining how much to plant, use viable seed numbers/acre, not bushels/acre. 

Table 1. Average HRS Seeding Rates Based on Seeds Per Pound at 90% Germination and 85% Emergence
HRSW	2002 On Fallow Minot	Lbs. Seed/A to Equal Million Live Seeds
HRSW	Seeds Per Pound	1.0	1.25	1.50
Ernest	16,214	81	100	122
Amidon	15,70	83	104	125
Hanna	16,156	81	101	122
Keene	18,160	72	90	108
Keystone	16,877	77	97	116
McKenzie	17,461	75	94	113
Parshall	16,509	79	99	119
Russ	15,929	82	103	123
Alsen	15,494	84	105	126
Argent	14,645	89	112	134
Briggs	16,214	81	101	122
Dandy	14,692	89	111	134
HJ98	18,306	71	89	107
Knudson	14,143	92	114	137
Mercury	14,740	87	111	131
Norpro	14,099	93	116	140
Reeder	15,133	86	108	129

Recent research conducted in several areas of N.D. indicate that for HRS wheat there is little or no advantage to planting more than 1.2 million viable seeds/acre.  (Table 2).  The one notable exception to this recommendation is for late-planted fields, where seeding rates greater than 1.2 million seeds are likely to improve yield potential (Figure 1).  The optimum seeding rate for durum appears to be in the 1.4-1.6 million seeds/acre range.

Table 2. Effect of seeding rate on wheat yield in ND, 2004
Location	Seeding Rates (seeds/acre)	Yield (bu/acre)+
Casselton	1.2 million	88.9**
	1.7 million	92.0
Carrington1	1.2 million	94.4N.S.
	1.7 million	94.0
Carrington2	1.0 million	71.9*
	1.75 million	69.8
Minot - HRS	1.2 million	49.6N.S.
	2.0 million	51.6
Minot - durum	1.0 million	44.7 N.S.
	1.5 million	46.8
+ N.S. means that there is no statistically significant difference between the values within an experiment, *, ** means there are statistically significance differences at the 5% and 1% level, respectively. Carrington1: evaluated seeding rate, variety, N rate, N timing Carrington2: evaluated seeding rate, variety, fungicide

Increasing seeding rates can increase the ability of a small grain crop to compete with weeds.  Therefore, the use of higher seeding rates may be justified in fields with difficult-to-control weeds and where herbicides are not used.  Most research indicates that increasing the seeding rate beyond the optimum recommended does not adversely affect yield, but it can increase the possibility of lodging, particularly in those varieties that are prone to lodging. Finally, data suggest that seeding rates need not be higher in no-till than in conventionally tilled systems.

Seeding depth: coleoptile length can matter
Within the range of 1.5 to 3 inches, the optimum seeding depth will depend on the condition of the soil at the time of planting, as seeds need moist conditions before they will germinate. A good rule of thumb is to seed as shallow as possible (but at least 1.5 inches deep) to place seed into moist conditions. 

As sowing depth increases, emergence is slowed and reduced which can translate into lower yield potential.  When circumstances require deeper seeding (i.e. 2.5 to 3 inches deep), be sure to use varieties with longer coleoptiles.   The coleoptile is the shoot that emerges from the seed and is a sheath that protects the first true leaf during emergence. Since coleoptile length is fairly closely correlated to the height of a variety, taller varieties with their longer coleoptiles should give greater latitude in seeding depth than the shorter semi-dwarf types.  Barley tends to have shorter coleoptiles than wheat and accordingly should not be planted as deep.

Factors that affect seed lot performance
Seed lots can vary significantly in characteristic such as seed size and germination percentage.  Seed size is determined by both the genetics of the variety as well as the environment in which it is produced.  Under favorable conditions, seed size will have little or no impact on stand establishment, as a typical seed will have adequate reserves to germinate and establish a seedling.  Seed lots with larger kernels, however, will have greater ability to emerge from depth and establish uniformly under difficult soil conditions.

Use seed lots with at least 85% germination, as declining germination indicates the potential for reduced vigor in the seed lot. In research recently conducted at NDSU with spring wheat and durum, we found that the accelerating aging test was a poor predictor of seed lot performance; if seed lots had good germination prior to accelerated aging, poor germination after accelerated aging did not mean that the seed lot would perform poorly in the field. This seed test is not recommended for small grains, though it does have value in soybeans and other legume crops.

Seed lots that have low falling numbers should be avoided, as it indicates that pre-harvest sprouting may have occurred.  Seed lots with pre-harvest sprouting will have reduced germination and poor vigor.  Similarly, seed lots from fields that were frosted during grain fill or that are “scabby” should be avoided. Frost damaged kernels will generally show up as small kernels or will have poor germination.  Seed lots with scabby kernels will have suboptimal performance due to reduced germination, and have the potential for increased seedling disease from the Fusarium fungus carried with the seed.  Conditioning can remove light kernels, and seed treatments with fungicides may help improve the performance of these seed lots. 

Less room for error with corn
The number of plants that represents an optimum stand in corn is but a tiny fraction of the number of plants needed for an optimum small grain stand.  Accordingly, there is less room for error when establishing a uniform stand of corn compared to small grains. 

Optimizing plant population for the conditions, reducing variability in plant to plant spacing and the timing of emergence can favorably impact corn yields.  Corn does not tolerate competition from weeds or other corn plants well as a seedling, and does not have the ability to fill in gaps as well as small grains. Having said that, the corn plant does have the ability to compensate for minor gaps by adding an extra ear or by producing a larger ear. 

Optimum plant populations of corn in N.D.
Optimum plant populations for corn have been rising dramatically over the past decades.  In the central Corn Belt, plant populations now exceed 32,000 plants per acre on most farms.  In North Dakota, the optimum plant population depends largely on the environment where corn will be planted, and the expected yield potential of the environment.

For highly productive areas of southeast N.D., the 32K is probably a reasonable upper limit for plant population. For areas where yield is not likely to exceed 100 bu, plant populations in the 28-30K range will be adequate.  Similarly, the best yields in the driest environments, where yield expectations are 60 bu or less, will probably be obtained with plant populations in the 15K to 18K range. Planting too many plants does not usually have a negative impact on yield, though the cost of seed is an important consideration.

Impact of plant uniformity and spacing on corn yield
There has been a plethora of research on the impact of plant to plant spacing uniformity on corn yield.  Recent data indicate that uniformity in spacing improves yield (as an example see Table 3). The following factors can impact the uniformity in plant to plant spacing:

Planter functionality. Check planter and component alignment, seed openers, depth wheels, press wheels, disk opener wear, chains, sprockets, metering and vacuum/air units. Given the size and complexity of modern planters, it is common to find adjustments that are needed that will improve planting uniformity.

Limit fertilizer placed with seed. Limit the amount of total N and K placed with the seed to less than 10 lbs per acre.  The salt effect of higher rates can reduce germination and adversely affect plant stands. 

Plant at an appropriate speed for your equipment.  Planting too fast will not only affect uniformity in seed drop, but can cause variation in planting depth, which can also adversely affect uniformity in the timing of plant emergence (see Table 3).

Table 3. Effect of planter and planting speed on within-row plant-spacing, days to emergence and yield (adapted from Liu et al., 2004. Agronomy Journal Vol. 96).
Planter type	Plant Spacing standard deviations		Days to 50% emergence		Yield (bu/acre)
	4.5 mph	7.1 mph	4.5 mph	7.1 mph	4.5 mph	7.1 mph
Vacuum meter	7.5	8.5	11.0	10.9	119.1	116.6
Finger pickup	9.3	11.4	11.0	11.0	114.9	115.0
Air seeder	19.3	20.4	12.2	12.8	109.7	114.3

Manage residue.  In no-till systems, residue can have an adverse impact on uniformity of emergence of corn. When planting into heavy residue, use and adjust residue managers (trash whippers) so that there is no hair pinning and so that the soil directly over the seed row remains free of residue. Planting no-till corn following a low residue-producing crop in N.D. is a good plan.

Ensure good soil seed contact. Once in the field, make sure there is good soil-seed contract.  Press wheels may not function properly if the soil is too wet.

Corn planting window
Higher corn grain yields will be obtained with early plantings. In most regions this means seeding between the last week of April and May 15. Early planting is recommended because the risk of fall frost damage is greater with each day planting is delayed. The risk increases rapidly after May 20 and seeding corn for grain production is not recommended after June 1. Date of planting studies have been conducted at Oakes, Casselton and Fargo, N.D., and in these studies approximately one bushel per day was lost by delay of planting during the month of May.

Seeding depth
In North Dakota when planting at the recommended planting date of May 1, soils can still be relatively cold, so planting depth can be an important consideration in establishing a uniform crop.  The recommended planting depth for corn is between 1.5 and 2 inches.  Planting too shallow may hasten emergence, but may also leave some seeds “stranded” in soil with insufficient moisture to allow for immediate germination.  Seeds planted at deeper depths will be in colder soils and will almost certainly be delayed in their emergence.

Uniformity in timing of plant emergence has been found to be more important than uniformity in plant to plant spacing. Seeding depth, residue management, planting speed, soil-seed contact, and seed bed preparation can all impact emergence variability and should be carefully monitored/managed.