This study was initiated in 1999 to determine if the levels of annual grass and broadleaf weed control provided by corn gluten meal (CGM) treatments can be explained by the nitrogen response of treated bluegrass and not herbicidal activity of CGM. The study is being conducted at the Iowa State University Research Station north of Ames, IA in an area of 'Parade' Kentucky bluegrass. The soil in this experimental area is a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with an organic matter content of 4.2%, a pH of 6.75, 17 ppm P, and 103 ppm K.
The experimental design is a randomized complete block with three replications. Individual experimental plots are 5 x 5 ft with five treatments. Corn gluten meal and urea are applied yearly to the same plots at an annual rate of 4 lbs N/1000 ft2 (Table 1). Treatments included split applications of 2 lb N/1000 ft2 and four applications of 1 lb N/1000 ft2. The CGM and urea are applied using cardboard containers as 'shaker dispensers'. The materials are watered-in with the irrigation system. Supplemental irrigation is used to provide adequate moisture to maintain the grass in good growing condition. In 2003, initial applications of all urea and CGM treatments were made on April 26. Sequential applications of 1 lb N/1000 ft2 were made on June 23, August 15, and September 14. The second applications of 2 lb N/1000 ft2 for urea and CGM (Treatment 3 and 5) were made on August 15.
Turf quality was monitored from May through September (Table 1). Visual turf quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst turf quality.
Crabgrass data represent the number of plants per individual plot. Crabgrass counts were made on August 4 and September 17 (Table 2).
Broadleaf weed populations were measured by either counting the number of plants or estimating the percentage cover per individual plot. Data for dandelion and clover were taken beginning in May and ending in September. Dandelion infestations were determined by counting the number of plants per individual plot. Clover populations were estimated by assessing the percentage area of each plot covered by clover.
Data were analyzed with the Statistical Analysis System (SAS) and the Analysis of Variance (ANOVA) procedure. Effects of CGM and urea on bluegrass quality and weed control were examined using Fisher’s Least Significant Difference (LSD) means comparison tests.
Table 1. Visual quality1 of Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.
| Material | Number of applications | May 21 | June 19 | July 10 | Aug 4 | Sept 17 | |
|---|---|---|---|---|---|---|---|
| 1 | Untreated control | NA | 4 | 4 | 5 | 4 | 3 |
| 2 | Corn gluten meal | 4 | 5 | 4 | 5 | 5 | 3 |
| 3 | Corn gluten meal | 2 | 6 | 6 | 6 | 5 | 3 |
| 4 | Urea (46-0-0) | 4 | 6 | 6 | 7 | 5 | 3 |
| 5 | Urea (46-0-0) | 2 | 5 | 4 | 6 | 4 | 2 |
| LSD0.05 | 0.64 | NS | NS | NS | NS |
1Visual quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst turf quality. Initial applications of all treatments were made on April 21. Sequential applications of treatments 2 and 4 were made on July 7, July 27, and September 5. The second applications of treatments 3 and 5 were made on July 27. NS = means are not significantly different at the 0.05 level.
Table 2. Crabgrass counts1 in Kentucky bluegrass treated in the 1999 Corn Gluten Meal/Urea Weed Control Study.
| Material | lbs N/1000 ft2 | Number of applications | August 4 | September 17 | |
|---|---|---|---|---|---|
| 1 | Untreated control | NA | NA | 3 | 5 |
| 2 | Corn gluten meal | 4 | 4 | 5 | 5 |
| 3 | Corn gluten meal | 4 | 2 | 1 | 3 |
| 4 | Urea (46-0-0) | 4 | 4 | 14 | 11 |
| 5 | Urea (46-0-0) | 4 | 2 | 8 | 11 |
| LSD0.05 | NS | NS |
1These values represent the number of crabgrass plants per plot covered. NS = means are not significantly different at the 0.05 level.
Table 3. Dandelion counts1 in Kentucky bluegrass treated in the 1999 Corn Gluten Meal/Urea Weed Control Study.
| Material | Number of applications | May 21 | June 19 | July 10 | Aug 4 | Sept 17 | |
|---|---|---|---|---|---|---|---|
| 1 | Untreated control | NA | 23 | 18 | 20 | 21 | 21 |
| 2 | Corn gluten meal | 4 | 21 | 23 | 18 | 21 | 19 |
| 3 | Corn gluten meal | 2 | 14 | 13 | 15 | 16 | 16 |
| 4 | Urea (46-0-0) | 4 | 14 | 14 | 13 | 15 | 14 |
| 5 | Urea (46-0-0) | 2 | 21 | 19 | 18 | 18 | 18 |
| LSD0.05 | NS | NS | NS | NS | NS |
1These values represent the number of dandelion plants per plot. NS = means are not significantly different at the 0.05 level.
Table 4. Percentage clover cover1 in Kentucky bluegrass treated in the 1999 Corn Gluten Meal/Urea Weed Control Study.
| Material | Number of applications | May 21 | June 19 | July 10 | Aug 4 | Sept 17 | |
|---|---|---|---|---|---|---|---|
| 1 | Untreated control | NA | 43 | 37 | 38 | 17 | 2 |
| 2 | Corn gluten meal | 4 | 22 | 17 | 28 | 20 | 6 |
| 3 | Corn gluten meal | 2 | 15 | 9 | 23 | 15 | 2 |
| 4 | Urea (46-0-0) | 4 | 14 | 8 | 13 | 13 | 4 |
| 5 | Urea (46-0-0) | 2 | 14 | 9 | 18 | 15 | 10 |
| LSD0.05 | NS | NS | NS | NS | NS |
1These values represent the area per plot covered by clover. NS = means are not significantly different at the 0.05 level.
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ISU Turfgrass:2004 Turfgrass Report | College of Agriculture |
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