Agronomy Gleanings
Vol. 96:1
March 29, 1996
In This Issue:
- Effect of Roundup Application Timings on Wirestem Muhly Control
- Evaluation of Narrow Row Corn for Grain and Silage Production in Pennsylvania
- Availability of Nitrogen from Manure Compost
- Evaluation of 'Alfagraze' Alfalfa in Pennsylvania
- Effect of Herbicide Application Timing on Hemp Dogbane Control in No-Till Corn
- Effects of Delaying N Application on Corn Growth and Yield
Greetings!
Our extension group has survived another snowy and cold Pennsylvania winter and is ready for spring and the upcoming growing season. One of our last winter activities is to summarize some of the research we've been conducting and sharing with folks at field days and other events. In this age of ever-changing and new technologies, we feel it's critical to get the results of these applied research projects in the hands of folks like you so that you can use them to make more effective management decisions in the crop production arena. This year we've pulled together a good sampling of some of the work that's been going on in our department during the past two years or so and I think you'll find some useful information in these reports. If you have questions concerning any of these studies, feel free to contact the authors.
This years Gleanings will be added to the World Wide Web at our Department of Crop and Soil Sciences Homepage at http://cropsoil.psu.edu/. Look for us there. Have a good year.
Sincerely,
Greg W. Roth
Editor
Effect of Roundup Application Timings on Wirestem Muhly Control
D. D. Lingenfelter and W. S. Curran
Wirestem muhly (Muhlenbergia frondosa) is a warm season, perennial, grass species that is becoming a problem throughout the region. It begins its growth in late spring and goes dormant by early fall. It reproduces by short, scaly rhizomes and seed and has an aggressive, bunch-type growth habit. With the decreased use of atrazine and the increase in conservation tillage systems, this late-emerging grass can be difficult to control. Effective control programs currently do not exist in no-tillage corn. However, with the introduction of Roundup Ready soybean varieties, post-applied Roundup (glyphosate) in soybeans may provide effective control of wirestem muhly. Also, wirestem muhly control could possibly be accomplished with a Roundup application before planting or after harvesting certain crops. The primary objectives of this study were to identify optimum Roundup application timings and to evaluate long-term effects on wirestem muhly.
Previous research in Illinois, Indiana, and Pennsylvania found that Roundup provided good control of wirestem muhly when compared to POST grass herbicides such as Fusilade (fluazifop) and Poast (sethoxydim). Research at Penn State University showed that Accent (nicosulfuron) and Beacon (primisulfuron) provided about 50 to 60% control of wirestem muhly in no-till corn. Also, Penn State researchers observed poor control with some POST grass herbicides in soybeans, but noted excellent wirestem muhly control in research trial alleyways treated with Roundup. With limited opportunities for wirestem muhly control in no-till corn, adequate control may be accomplished in a rotational crop or between crops The use of a glyphosate-tolerant crop, such as Roundup Ready soybeans, can allow timely, over-the-top applications of Roundup. Applications of Roundup in early or late summer also may be an alternative to control wirestem muhly. However, optimal application timings have not previously been studied.
Study Description
In 1994 and 1995, field studies were conducted in central Pennsylvania on fallow land heavily infested with wirestem muhly to examine various application timings of Roundup. Roundup, plus 0.25% (v/v) nonionic surfactant, was applied at 1.0 pint/acre and 2.0 pints/acre at two week intervals from mid May through mid October (or first killing frost). Herbicides were applied to small plots with a CO2 -backpack sprayer that delivered 10 gallons/acre. The trials were randomized and replicated. No crop was planted in the trial area during the entire study. Visual ratings of per cent control and above-ground vegetation (biomass) were collected during the summer.
Applied Questions
Which Roundup application timing provided the most effective season-long and long-term control of wirestem muhly?
The end of season visual ratings revealed that Roundup provided 90 to 100% control of wirestem muhly from applications made in mid June to early October. Applications made prior to these dates did not provide adequate control (Figure 1). Biomass data was highly correlated to visual ratings.
First year evaluations taken the year after application show that Roundup provided greater than 90% control for application timings from late June 1994 to early September 1994. Ratings taken in August 1995 showed Roundup still provided about 65 to 80% control of wirestem muhly over the same time period (Figure 2). The treatment areas again were not planted to any crop, so crop competition was not a control factor.
How can this knowledge be used practically to manage wirestem muhly?
A timely Roundup application should provide good control of wirestem muhly into the following season. However, management techniques must be incorporated into rotational crops for proper control of wirestem muhly. This research shows that a Roundup application beginning in mid to late June and as late as early September can provide effective control of wirestem muhly. Now that Roundup Ready soybean varieties are commercially available, producers can use this new technology to assist in managing wirestem muhly and other weedy plants.
Other opportunities for timely application of Roundup for wirestem muhly control occur prior to planting double crop soybeans or certain vegetable crops, or after small grain or vegetable crop harvest. A diverse crop rotation and the use of the latest technology will greatly assist Pennsylvania producer's ability to manage problem weeds such as wirestem muhly.
Figure 1. The effect of Roundup application timing on wirestem muhly control the year of application.
Figure 2. The effect of Roundup application timing on wirestem muhly control the year after application.
Evaluation of narrow row corn for grain and silage production in Pennsylvania
Greg W. Roth
Previous research that has compared narrow (15-20 inch) corn row production to conventional 30 inch rows has indicated that the yield response to narrow rows is somewhat inconsistent among hybrids, environments and plant populations. To take advantage of narrow rows in corn production, there is a need to better understand the factors that influence the response to narrow corn production. We were interested in evaluating the response to narrow rows under the production conditions experienced in the Pennsylvania. Theoretically, an equidistant plant stand should minimize interplant competition and result in higher yields. Yield responses to narrowing rows to less than 30 inches have been generally positive but somewhat inconsistent, however, and the factors that influence the response to narrow rows are not well understood. In addition, the investment required for equipment modifications and some of the practical considerations associated with narrow rows will limit the adoption of narrow row production. Since 1993, we have conducted a total of 10 experiments which have evaluated the potential of narrower rows and higher plant populations for corn grain and silage production in Pennsylvania.
Study Description
Our initial studies were established in 1993 and 1994 at Rock Springs in central Pennsylvania. Each study included three factors: two row spacings (15 vs. 30 inches), 2 plant populations (27 and 34,000 plants per acre) and two hybrids. The nitrogen fertility program at each site consisted of 160 pounds of N applied prior to planting. The experiments were planted no-till on May 2, 1993 and May 9, 1994 and irrigated twice in both years.
Eight on-farm field studies were established in 1994 and 1995 to evaluate the yield response of corn harvested for silage. In each trial three treatments were evaluated, which included a normal population (27,000 ppa) in 30 inch rows, a high population (34,000) in 30 inch rows and the high population in 15 inch rows. Four of the sites were planted with 15 inch planters and four were planted with a 30 inch planter, doubling back in the 15 inch row treatment. These experiments were overplanted and not thinned.
Applied Questions
Was there a grain yield response to reducing the row spacing to 15 inches?
Yes, averaged over both years, hybrids and populations, reducing the row spacing to 15 inches increased yields by 4.2% from 165 to 172 bu/A. (Table 1)
| Row Spacing | 1993 | 1994 | Mean |
|---|---|---|---|
| (in) | ------------------------------- Bu/A-------------------------- | ||
| 15 | 182 | 163 | 172 |
| 30 | 175 | 155 | 165 |
| Mean | 178 | 159 | 168 |
Were there consistent differences in the way hybrids responded to reducing the row width?
No, in 1993, 3573 showed the greatest response to narrow rows while in 1994 3525 was more responsive to narrow rows. (Table 2). We anticipated that the more upright leafed 3525 would be more responsive to narrow rows, but this was not the case in 1993. The lack of consistent hybrid differences was also reported by Dr. Bob Nielsen at Purdue in the 1980's.
| Year | Row Width | 3573 | 3525 | Mean |
|---|---|---|---|---|
| ------------------------ Bu/A----------------- | ||||
| 1993 | 15 | 187 | 176 | 182 |
| 1993 | 30 | 174 | 176 | 175 |
| Response | +13 | 0 | +7 | |
| 1994 | 15 | 164 | 161 | 162 |
| 1994 | 30 | 160 | 150 | 155 |
| Response | +4 | +11 | +7 | |
Was there a greater yield response to higher populations in narrow rows?
Yes, on the average the yield increase from increasing populations was 14.5 bu/A in 15 inch rows and 8.5 bu/A in 30 inch rows (Table 3). In 1993, yields increased by 8 bushels per acre with the increased population in 15 inch rows but there was no response to population in the 30 inch rows. In 1994, the yield response to increased population was much greater than in 1993 due to a stressful early season followed excellent conditions the rest of the season the season. Our results also showed that under the conditions of this study, i.e., 105 d maturity with little moisture stress, corn yields can respond to higher plant populations with narrow rows.
| Row Spacing | Population | 1993 | 1994 | Mean |
|---|---|---|---|---|
| (in) | ------------------- Bu/A ----------------- | |||
| 15 | 27000 | 178 | 153 | 165 |
| 15 | 34000 | 186 | 174 | 180 |
| Response | +8 | +21 | +15 | |
| 30 | 27000 | 174 | 147 | 160 |
| 30 | 34000 | 175 | 163 | 169 |
| Response | +1 | +16 | +9 | |
Were there consistent trends in the response of kernel number or kernel size to row spacing?
In both years there was a tendency for larger kernels in the narrow rows. Averaged over both years, the kernel size increased by 2.0% from 29.2 mg in 30 inch rows to 29.8 mg in the 15 inch rows. The number of kernels per ear also increased 2.7% with the narrow rows in both years from 505 kernels/ear in the 30 inch rows to 519 kernels/ear. Consequently, the advantage of narrow rows was due to improvements in both ear development and the grain fill periods.
Was there a silage yield response to reducing the row spacing to 15 inches?
In four of the eight trials, reducing the row spacing and increasing the plant populations increased yields. Averaged over the eight locations, the silage yield response to narrow rows was approximately 10%, similar to what we anticipated, based on previous estimates on silage yield responses to narrow rows measured in New York. There was some tendency for larger yield responses in shorter season environments like Rock Springs in 1994 and Bradford County in 1995. The response to plant population alone was significant at one of the eight sites. Forage quality was generally not affected by row spacing or population except where the cooperators exceeded 34,000 ppa in the narrow row treatments. In the two cases where this occurred silage energy levels were reduced by 5-10%.
Are narrow rows a practical alternative for Pennsylvania corn growers?
Based on our experience narrow rows may offer yield advantages of 5% for grain and 10% for silage, although this response seems to vary among seasons and locations. Other advantages of narrow rows are weed control, soil erosion reduction, the opportunity to use one planter for both corn and soybeans and increased nutrient uptake associated with narrow rows. Disadvantages include retooling costs and higher seed and insecticide costs. The potential of narrow rows for individual producers will depend on individual economic decisions and adaptability to the farming operation.
Availability of Nitrogen from Manure Compost
Douglas Beegle and Randy Bowersox
Composting of manure has been proposed to play a role in manure management programs designed to protect water quality. It is known that the biological activity involved in composting can reduce the nutrient content and changes the nutrient availability of the material. In this way composting is a form of manure treatment that may contribute to alleviating some of the on-farm manure nutrient excess problems. When manure is moved from a farm with an excess to a farm with a deficit of nutrients, there are several concerns that compost can address. Composting reduces the amount of material to be transported. This is critical because one of the main limitations to moving manure is the high cost of moving the low analysis bulky material. Composting reduces the hazards from weeds and diseases because of the high temperatures involved in the composting process. Odors are usually reduced by composting. Finally, composting improves the perception that the public has about the material. There is much greater public acceptance of compost than raw manure, regardless of the properties of either material. Thus, composting manure could play a role in dealing with the potential environmental problems related to manure nutrients faced by Pennsylvania farmers. However, the main question related to use of composted manure for crop production is the availability of the nutrients in composted manure and the factors that govern this availability. The objective of this study was to determine the availability of the nitrogen in composted manure for corn production under field conditions.
Study Description
Field plots were established with farmer cooperators in Centre Co., Montour Co., Columbia Co., and Lancaster Co. over the three years of the research. In Centre, Montour, and Columbia Co. the manure was dairy. At Lancaster Co. the manure was poultry. At each location manure and compost made from that same manure were applied at rates to supply equal amounts of total N regardless of the source. All plots were planted to field corn following the cultural practices used by the individual farmers. Soil and plant samples were collected from all plots. Pre-sidedress soil nitrate tests (PSNT) were also run at each location to evaluate the efficacy of this test where compost has been applied. All plots were sampled after harvest for Mehlich 3 soil tests and for residual nitrogen. After the initial year only the fertilizer treatments were repeated in subsequent years. No additional manure or compost was applied at these locations. This enabled us to look at residual effects of the manure and compost.
Applied Questions
Were there differences in the nutrient content of the manure and compost ?
Yes, there were considerable differences. The analysis of manure and compost applied in the first year of the field studies are summarized below. Note especially the lower NH4-N content in the compost compared to the manure. Since this is the readily available fraction of the nitrogen, this would indicate lower immediate availability of the compost compared to the manure.
| Material | Loc. | Total N | NH4-N | Org. N | Total P | Total K | Solids | C:N |
|---|---|---|---|---|---|---|---|---|
| ------------------------------ % ----------------------------------- | ||||||||
| Dairy Manure | Centre | 2.56 | 0.69 | 1.87 | 0.41 | 1.02 | 22.85 | 14.0 |
| Dairy Compost | Centre | 1.28 | 0.23 | 1.06 | 0.36 | 0.85 | 30.63 | 22.7 |
| Dairy Manure | Mont.& Col. | 1.60 | 0.46 | 1.13 | 0.18 | 1.82 | 33.90 | 33.9 |
| Dairy Compost | Mont.&Col. | 2.42 | 0.01 | 2.41 | 0.73 | 2.61 | 24.31 | 19.45 |
| Poultry Manure | Lanc. | 4.58 | 1.5 | 3.08 | 2.25 | 1.79 | 28.97 | 6.3 |
| Poultry Compost | Lanc. | 2.15 | 0.06 | 2.09 | 2.93 | 2.06 | 34.81 | 8.8 |
Note also the difference between the two dairy manure and compost samples. The manure from Centre Co. was raw manure from a free stall barn with little bedding and thus it had a low C:N ratio. Consequently a large amount of straw had to be added to the manure to make the compost. This dilution with the straw resulted in a lower nitrogen concentration in the compost compared to the manure. The other dairy manure contained a large amount of bedding and thus had a lower nitrogen content and higher C:N ratio. To make compost from this manure no additional straw had to be added and thus as the carbon was burned off the nitrogen was concentrated and the nitrogen content of this compost is higher than the manure. The main point here is that all composts are not the same and analysis for both total and NH4-N are critical.
Were there differences in the corn yields between the manure and compost treatments?
Yes, yields were consistently higher in the manure treatment compared to the compost treatment even though equal amounts of N were applied from both sources (Table 2). This is an indication of the higher nitrogen availability from the manure compared to the compost. With a few exceptions the PSNT data for nitrogen availability followed the same trend also indicating higher nitrogen availability from the manure. At the end of the year, residual nitrate levels in the soils were all very low and there were no differences in left-over nitrate between the manure and compost treatments.
| Experiment | Compost | Manure | Compost | Manure |
|---|---|---|---|---|
| Yield (bu/A) | PSNT (ppm) | |||
| First Year | ||||
| Lancaster 1993 - Poultry | 89 | 80 | 47 | 50 |
| Centre 1993 - Dairy | 104 | 132 | 22 | 26 |
| Montour 1994 - Dairy | 82 | 94 | 14 | 19 |
| Columbia 1994 - Dairy | 115 | 128 | 23 | 20 |
| Second Year | ||||
| Lancaster 1994 - Poultry | 83 | 103 | 22 | 20 |
| Centre 1994 - Dairy | 103 | 110 | 22 | 23 |
| Montour 1995 - Dairy | 21 | 30 | 9 | 13 |
| Columbia 1995 - Dairy | 93 | 101 | 9 | 11 |
| Third Year | ||||
| Centre 1995 - Dairy | 33 | 34 | 12 | 12 |
How did the N availability from the compost and manure compare to "book" values?
Four nitrogen fertilizer rates were applied to determine the nitrogen response at each location. From this response curve the fertilizer equivalents of the manure and compost treatments and thus the nitrogen availability factors were determined. These average availability factors for the manure and the compost are summarized in Table 3 for the dairy manure. Factors could not be determined for the poultry manure in these experiments because of a lack of nitrogen response at this location, likely due to a history of heavy poultry manure applications. This is confirmed by the high PSNT levels for this location (Table 2-Lancaster). Table 3 also contains book values for nitrogen availability that have been proposed. The results of this work agree very closely with the book values.
| Material | % Organic N Available1st year* | % Organic N Available 2nd year | ||
|---|---|---|---|---|
| Results | Book | Results | Book | |
| % Available | ||||
| *Assumes 35% availability of NH4-N | ||||
| Manure | 23 | 25 | 10 | 12 |
| Compost | 13 | 10 | 5 | 5 |
Application of the results:
On the basis of these results it is proposed to modify Table 2-14 in the Penn State Agronomy Guide to include nitrogen availability factors for compost. The proposed revision follows:
Evaluation of 'Alfagraze' Alfalfa in Pennsylvania
M.H. Hall and L.E. Marshall
Alfalfa is a deep rooted plant that maintains relatively high forage production in mid-summer when production of other shallow-rooted, cool-season forages has slowed or stopped. This has always made alfalfa and appealing crop in grazing systems which are based around cool-season forages. Unfortunately, bloat and poor persistence, have inhibited the wide acceptance of alfalfa into grazing systems. Until recently, farmers had little hope, other than better management, in overcoming these problems. Recently, however, alfalfa breeding programs have begun to address the problem of poor alfalfa persistence under grazing situations.
Alfagraze alfalfa was selected for its persistence under conditions of continuos grazing by Dr. Joe Bouton at the University of Georgia. The release of this variety in 1989 enhanced a renewed interest in the use of alfalfa in grazing systems. While greater persistence under grazing has been reported in states south of the Mason-Dixon line, no information about Alfagraze persistence and herbage production under grazing conditions was available in more northern States. In alfalfa variety test harvested four times each year for hay; however, Alfagraze was not a top performer. The objectives of this research were to evaluate Alfagraze alfalfa for persistence and production under simulated grazing conditions in Pennsylvania.
Study Description
Alfagraze and 'Apollo Supreme' alfalfa were band seeded at 15 lb/acre into a tilled seedbed in April of 1991 in central Pennsylvania at the Russell E. Larson Agric. Research Center. Apollo Supreme is a multiple disease resistant alfalfa variety that yielded well in Pennsylvania trials. Both varieties were harvested twice during the seeding year at 1/10 bloom. In the spring of 1992, harvest treatments of 21, 28, and 35 d frequencies were implemented and continued through the 1995 growing season. Harvest treatments were initiated in the spring so that the final harvest of the growing season for all treatments was on the same day in early September. This harvest frequency resulted in 4, 5, and 6 harvests/year for the 35, 28, and 21 d frequency, respectively. Yield of both varieties was monitored at each harvest and persistence (plants per square foot) determined in October of each year.
Applied Questions
Is Alfagraze more persistent than a hay type (Apollo Supreme) variety under simulated grazing conditions in Pennsylvania?
No difference was observed between either variety over the duration of the study (Fig. 1). There were no interactions between harvest frequency and variety for persistence. More frequent harvests (21 d) were more deleterious than less frequent harvests (35 d) initially, but by the end of the fourth year no difference was observed (Fig. 2).
Does Alfagraze yield more than Apollo Supreme under frequent harvests (similar to grazing)?
There were no differences between varieties when harvested at the same frequency (Fig. 3). The greatest yield differences occurred between harvest frequencies (Table 1). Yields for all harvest frequencies were similar in 1995 because of drought stress during the growing season.
| Harvest frequency |
Alfagraze | Apollo Supreme |
|---|---|---|
| d | ------------------------- ton/acre ------------------------- | |
| 21 | 16.4 | 16.6 |
| 28 | 17.1 | 17.6 |
| 35 | 22.1 | 22.2 |
Effect of herbicide application timing on hemp dogbane control in no-till corn
William S. Curran, Paul H. Craig and Edward L. Werner
Hemp dogbane (Apocynum cannabinum) is an herbaceous creeping perennial that is native to North America. It is found throughout Canada, the United States, and especially the mid-Atlantic region. Hemp dogbane is a serious problem weed in both cultivated and noncultivated fields in many parts of Pennsylvania. Although crop reduction due to hemp dogbane varies, some research from Nebraska showed a 15 percent reduction in corn, 32 percent loss in sorghum, and 37 percent loss in soybean grain yield from uncontrolled infestations. In conventional tillage systems, hemp dogbane is rarely a serious weed problem. However, with the increase in conservation tillage systems and lack of effective selective herbicides, hemp dogbane has quickly become a serious problem.
Hemp dogbane is seldom a problem in fall seeded winter annual crops such a winter wheat or barley or in perennial hay crops such a alfalfa. However, control in corn and soybeans is difficult with short-term suppression and preventing an impact on this year's crop yield often being the best that can be expected. A crop rotation that allows alternative herbicides, application timings, and/or selective tillage can help reduce hemp dogbane populations to more manageable levels. Although application of a systemic herbicide during the late summer or early fall is often mentioned as an effective tool or hemp dogbane control, little information is available on the potential effectiveness of this strategy. In theory, late summer application of herbicides such as Roundup, Banvel, or 2,4-D to hemp dogbane may more effectively move the systemic herbicide to underground vegetative plant parts.
Study Description
In the fall of 1993 and 1994, a study was established in Dauphin County to compare fall application of several systemic herbicides to an early summer application in corn. Previous to the fall treatments, the hemp dogbane was allowed to regrow following either wheat harvest in early July or in a fallow field situation. Both field locations had a history of no-tillage. Fall herbicide treatments included Roundup at 1 and 2 quarts per acre, Banvel at 1 and 2 pints per acre, Banvel plus 2,4-DLVE at 1 pint each per acre, and Roundup plus 2,4-DLVE or Banvel at 1 quart plus 1 pint. Herbicides were applied at two application timings either in early September or in early October. Corn was planted no-till the following spring. Both years, a burndown herbicide plus a soil residual grass plus broadleaf program was applied prior to corn planting. Postemergence herbicide treatments in corn included Banvel or 2,4-D amine at 1 pint per acre and Beacon plus Banvel at 0.38 oz plus 1/2 pint per acre. All herbicide treatments included a nonionic surfactant at 1 quart per 100 gallons in the spray mixture. Final treatments included fall application of Roundup at 1 quart per acre plus an early summer application of Banvel at 1 pint.
Applied Questions
The hemp dogbane infestation was severe throughout most of the corn study in 1994. Overall, hemp dogbane control was better in 1995, although the infestation was less severe and more variable.
How effective were the fall herbicide treatments?
Treatments that included fall applied Roundup were clearly visible in early summer showing good control of hemp dogbane and several other perennial weeds in the field. The emergence of new shoots throughout the summer in some treatments reduced the performance ratings by August (see the accompanying table). The addition of Banvel or 2,4-D to Roundup did not improve overall performance on hemp dogbane, although including 2,4-D did improve the control of dandelion (data not shown). In general, Banvel and 2,4-D performance was less consistent than Roundup. The September and October timings produced similar results, although the September timing may have had a slight advantage in 1994 because of cold weather and a light frost just prior to the October application.
How effective were the post herbicide treatments?
In general, the post applications in corn were equal or less effective than the fall applications. Although we did not continue to evaluate hemp dogbane recovery over time, the residual control of the early June applications may have been less than the fall applications. One of the better treatments included fall application of Roundup followed by an postemergence application of Banvel in corn. The fall treatment followed by an early summer control should allow for better control of a number of perennial weeds.
| Herbicide | Rate | Timing | 1994 | 1995 | 94/95 ave |
|---|---|---|---|---|---|
| (pints) | ---------------% control------------------ | ||||
| Roundup | 2 | Sept. | 82 | 85 | 83 |
| Roundup | 4 | Sept. | 78 | 93 | 86 |
| Banvel | 1 | Sept. | 77 | 82 | 79 |
| Banvel | 2 | Sept. | 63 | 87 | 75 |
| Banvel+2,4-D | 1+1 | Sept. | 75 | 82 | 78 |
| Roundup+Banvel | 2+1 | Sept. | 73 | 86 | 80 |
| Roundup+2,4-D | 2+1 | Sept. | 68 | 86 | 77 |
| Sept. ave. | 74 | 86 | 80 | ||
| Roundup | 2 | Oct. | 67 | 92 | 79 |
| Roundup | 4 | Oct. | 68 | 90 | 79 |
| Banvel | 1 | Oct. | 58 | 77 | 68 |
| Banvel | 2 | Oct. | 63 | 67 | 65 |
| Banvel+2,4-D | 1+1 | Oct. | 70 | 70 | 70 |
| Roundup+Banvel | 2+1 | Oct. | 62 | 86 | 74 |
| Roundup+2,4-D | 2+1 | Oct. | 63 | 83 | 73 |
| Oct. ave. | 65 | 81 | 73 | ||
| Banvel | 1 | June | 57 | 82 | 69 |
| 2,4-D | 1 | June | 67 | 72 | 69 |
| Beacon+Banvel | 0.38oz + 0.5 | June | 63 | 70 | 67 |
| June ave. | 62 | 75 | 68 | ||
| Roundup+Banvel | 2+1 | Sept.+ June | 85 | 94 | 90 |
| Roundup+Banvel | 2+1 | Oct.+ June | 80 | 95 | 87 |
| Split ave. | 82 | 94 | 88 | ||
| LSD (0.05) | 19 | 11 | 14 | ||
Why did none of the herbicide treatments provide perfect control?
Hemp dogbane shoots can emerge throughout the summer or shoot buds may lie dormant until some environmental signal stimulates growth. This prevents a single timely treatment with an effective systemic herbicide. This phenomena may be more typical in a no-till environment where root and shoot buds lie undisturbed in the soil. Some tillage prior to or following herbicide application could improve the performance of the herbicide program.
What are some other possibilities for hemp dogbane management?
In 1996, our research will attempt to address the effect of tillage on hemp dogbane control in corn. With the introduction of Roundup-Ready soybeans in 1996, and Liberty-Link corn and soybeans over the next few years, better management of hemp dogbane in summer annual cropping systems is almost certain. However, long-term control of hemp dogbane as well as other herbaceous and woody perennial weeds may still require a more diverse crop rotation that allows alternative herbicides, application timings, and the selective use of tillage.
Effects of Delaying N Application on Corn Growth and Yield
S.E. Smith and G.W. Roth
The timing of N fertilizer applications to corn can affect both corn yields and the potential for nitrate leaching from the soil. Delaying the bulk of the N applied to corn until after the four to eight-leaf stage, a practice known as sidedressing, has been recommended as a best management practice and is widely used by corn producers. Potential benefits of this practice are improved yields, better N utilization, and less potential for nitrate leaching in the spring. Sidedressing has been shown to be most beneficial on fields that have a recent manure history or legume residual N history. However, several studies have indicated that the benefits of sidedressing may be inconsistent. In some instances, sidedressed corn on fields with little residual soil N availability has developed an early season N deficiency that resulted in yield loss. Nitrogen deficiency can also result from dry weather following sidedress N application which results when the fertilizer remains in the soil surface where root and soil microbial activity are limited. The objective of this study was to determine how delaying N fertilizer application on fields that have little residual N availability affect dry matter yield throughout the growing season, grain yield and residual soil nitrate after harvest.
Study Description
A two year study was conducted at four locations in Pennsylvania to evaluate three N timing application treatments: all of the N applied at planting; split application of N (40% at planting, 60% at V8); all N applied as a sidedress at V8. Each location had no manure or legume residual N history. In 1994, experiments were conducted in Port Matilda and Rock Springs and in 1995 in Huntingdon and Rock Springs. The soils at Rock Springs are described as well-drained, deep limestone soils and at the other two locations are described as well-drained, shallow shale soils. Dry matter yield was estimated at seven plant growth stages by sampling five consecutive plants from each plot. Grain yield was estimated by harvesting and weighing corn ears from 23 ft of the two middle rows of each plot at physiological maturity. Soil samples were taken from each location after grain harvest and analyzed for soil nitrate colorimetrically using a Technicon Autoanalyzer.
Applied Questions
Was dry matter yield during the season affected by sidedressing?
Delaying N until V8 resulted in reduced dry matter yield due to N deficiency at each of the four locations. Figure 1 shows that the sidedress treatment at Rock Springs in 1994 had reduced dry matter accumulation during late vegetative growth stages and early reproductive growth stages.
Figure 1. Dry matter yield response to delayed N application.
Was final grain yield affected by sidedressing?
The grain yield response to delaying the N application was inconsistent at the four locations (Table 2). The sidedress V8 treatment resulted in a significantly lower grain yield compared to the at plant treatment at Rock Springs 1994 but a higher yield at Rock Springs 1995. The timing of rainfall during the season and other stress factors apparently influenced the performance of the sidedress at V8 treatment. As a result, the yield benefits of sidedressing at V8 were not consistent.
Did sidedressing affect the residual soil nitrate at the end of the growing season?
Delaying N application until sidedress at V8 resulted in more nitrate remaining in the root zone than the at plant treatment. (Figure 3) Significantly more nitrate remained in the soil after harvest with delayed N application on both the shaly (Port Matilda and Huntingdon) and the limestone (Rock Springs) soils. The higher level of soil nitrate remaining after harvest needs to be balanced with the reduced early season leaching potential which is a recognized benefit of delayed N applications.
What are the implications of this study?
Where residual N levels are low, relying on a V8 sidedress application to supply the bulk of the N requirement can be risky, since early season N deficiency can reduce growth and occasionally limit grain yields. In these situations, a split application, an earlier sidedress application or an at planting application would likely be better.