Agronomy Journal 92:144-151 (2000)
© 2000 American Society of Agronomy
SOIL MANAGEMENT
Cover Crops for Sweet Corn Production in a Short-Season Environment
Tim Griffina,
Matt Liebmana and
John Jemison, Jr.a
a Department of Agronomy, 3218 Agronomy Hall, Iowa State University, Ames, IA 50011-1010 USA
tgriffin{at}umext.maine.edu
 |
ABSTRACT
|
|---|
Legume cover crops can supply all or most of the N required by a subsequent crop if legume biomass is of sufficient quantity and N mineralization is approximately synchronous with crop demand. Three 2-yr crop rotation cycles were conducted on a Lamoine silt loam (fine, illitic, nonacid, frigid Aeric Epiaquept) soil in Maine to (i) evaluate biomass and N accumulation of alfalfa (Medicago sativa L.), winter rye (Secale cereale L.), and hairy vetch (Vicia villosa Roth subsp. villosa) plus winter rye cover crops; (ii) determine sweet corn (Zea mays L.) response to legume and fertilizer N sources in a barley (Hordeum vulgare L.)–sweet corn rotation; and (iii) assess the accuracy of the presidedress soil nitrate test (PSNT) and leaf chlorophyll N test (LCNT) for distinguishing N-responsive and nonresponsive sweet corn. Both legumes accumulated more N than rye grown alone, although total biomass was similar. Sweet corn following rye always exhibited a linear response to N fertilizer (up to 156 kg N ha-1), but generally exhibited no response to added N following either alfalfa or hairy vetch plus winter rye (VR). Both PSNT and LCNT were 75% accurate in identifying plots responsive to additional fertilizer N. The legume cover crops grown were able to replace all or nearly all of the N fertilizer required by a subsequent sweet corn crop, with fertilizer replacement values (FRVs) of 58 to 156 kg N ha-1 in a short-season environment. These cover crops are a viable alternative source of N, greatly reducing or eliminating the need for N fertilizer.
Abbreviations: FRV, fertilizer replacement value • LCNT, leaf chlorophyll N test • PSNT, presidedress soil nitrate test • VR, hairy vetch plus winter rye • DM, dry matter
|
INTRODUCTION
|
|---|
PRODUCTION systems that utilize N-fixing legumes as a primary N source for subsequent nonlegume crops include full-season green manure crops, interseeded legumes, and cover crops. Each of these options present significant management challenges to producers interested in reducing fertilizer N inputs or producing crops without fertilizer N. For example, full-season green manure crops, while potentially having the greatest impact on soil quality and pest/weed cycles (Altieri, 1995; Biederbeck et al., 1998), may not be economically viable because of the loss of income from that field for an entire growing season. Interseeding legumes with or into a standing crop is common in small grains like wheat (Triticum aestivum L.) and oat (Avena sativa L.). Bruulsema and Christie (1987), Hesterman et al. (1992), and Stute and Posner (1995) demonstrated that this system can result in significant contributions of N to a subsequent corn crop. However, interseeding into a widely spaced row crop like corn or soybean [Glycine max (L.) Merr] may require specialized equipment and additional field operations, and competition between the interseeded and main crops also can be problematic (Kumwenda et al., 1993).
Cover crops, generally grown over the winter between harvest of one crop and planting of a subsequent crop, can overcome at least some of the obstacles associated with green manure and interseeded crops. It is well-documented that cover crops can supply sufficient N for production of a subsequent grain crop with little or no supplemental N fertilizer. McVay et al. (1989) found minimal corn yield response to N fertilizer following hairy vetch or crimson clover (Trifoilium incarnatum L.) cover crops, compared with corn following wheat. Burket et al. (1997) compared sweet corn yield following clover (Trifolium pratense L.), rye, and rye plus pea (Pisum sativum L.) cover crops, finding that both legume cover crops replaced approximately 150 kg fertilizer N ha-1. Cover crop N contributions to vegetable crops also can be substantial. Stivers and Sheehan (1991) evaluated the use of cover crops for tomato (Lycopersicon esculentum var. esculentum), demonstrating that yields were similar using cover crops and fertilizer N sources. There were minimal responses to fertilizer N following legume cover crops. Skarphol et al. (1987) used legume cover crops to supply N for snap bean (Phaseolus vulgaris L.). Bean yields following legume cover crops were similar to yields obtained with 90 kg fertilizer N ha-1 without a legume cover crop.
The use of cover crops in cool, northern climates can present additional production challenges, including: (i) limited opportunity for cover crop seeding and establishment; (ii) potentially small accumulation of cover crop biomass and N, especially if the cover crop is seeded after the main crop harvest; and (iii) the rate of cover crop decomposition and N mineralization, a function of both cover crop composition and temperature, may not keep pace with subsequent crop demand. In fact, these criteria of successful establishment, sufficient biomass and N accumulation, and synchrony between N mineralization and crop demand must be met for a cover crop to be viable in any crop system. The availability of reliable in-season N tests (either tissue- or soil-based) would better allow timely decisions on supplemental N applications following cover crops. Our research addresses these potential constraints to cover crop use in short-season conditions, evaluating cover crop options within a 2-yr barley–sweet corn rotation. The use of a cool-season small grain as the first-year crop allows additional flexibility for cover crop seeding and establishment; cover crops can either be interseeded with the barley or sown after barley harvest. In both cases, there is usually sufficient time for cover crop establishment. Sweet corn, as the test crop, responds to legume and fertilizer N application. It can be grown in a short (90–100 d) season environment, although economic return is usually less for later planted crops. The PSNT (Magdoff et al., 1984; Fox et al., 1989) developed for field corn has been successfully used in sweet corn production (Heckman et al., 1995), while the accuracy of the LCNT (Blackmer and Schepers, 1995) has not been assessed for sweet corn. The specific objectives of our research were to evaluate: (i) alfalfa, winter rye, and VR cover crop biomass and N accumulation; (ii) response of a subsequent sweet corn crop to cover crop and fertilizer N application; and (iii) accuracy of PSNT and LCNT in predicting sweet corn response to cover crop and fertilizer N sources.
|
Materials and methods
|
|---|
Research was conducted from 1992 to 1995 at the University of Maine Sustainable Agriculture Research Farm in Stillwater, ME (44°56' N, 68°42' W). Soil type was a Lamoine silt loam (USDA-SCS Soil Survey Staff, 1992), on a 0 to 2% slope. Soil nutrient levels in 1992, from analysis by the University of Maine Analytical Laboratory, were: pH 6.3 (1:1, soil:water), cation exchange capacity (CEC) 8.8 cmol kg-1, 9.1 kg P ha-1, 215 kg K ha-1, 323 kg Mg ha-1, and 2276 kg Ca ha-1, determined using a pH 3.0 1 M NH4Ac extractant and inductively coupled plasma emission spectroscopy. Soil organic matter was 45 g kg-1, measured by loss on ignition. Phosphorus was applied as triple superphosphate (0–46–0 N–P–K) and K was applied as KCl (0–0–60 N–P–K), before barley and sweet corn planting in each rotation cycle, according to soil test recommendations from the University of Maine Analytical Laboratory. In 1994 and 1995, Zn (2.25 kg ha-1) was applied prior to planting sweet corn, as soil Zn levels were less than 1.0 mg kg-1 soil.
Three rotation cycles (2-yr each) were conducted, beginning in 1992 (Cycle I), 1993 (Cycle II), and 1994 (Cycle III). Barley and cover crop establishment occurred during Year 1 and cover crop incorporation and sweet corn production during Year 2 of each rotation cycle. Calendar dates for field operations and crop and soil sampling are provided in Table 1
and climate information is shown in Table 2
. Barley was seeded at 125 kg ha-1, using a grain drill without packer wheels, at 20 cm row spacing. Alfalfa (cv. Saranac) was broadcast (13.5 kg ha-1) immediately after barley planting on appropriate plots (3.25 by 10.7 m) and the entire experimental area was cultipacked to enhance seed-to-soil contact. Barley was harvested but yields were not measured. Following barley harvest, straw was incorporated using a tractor-mounted rototiller, except in plots interseeded with alfalfa. Winter rye (cv. Aroostook; 112 kg ha-1) and hairy vetch (cv. Madison; 56 kg ha-1) plus winter rye (56 kg ha-1) were then planted using a grain drill, with 20 cm row spacing. Newly planted plots were then cultipacked.
In late May, cover crops were flail mowed and incorporated with a rototiller (Cycle I) or moldboard plow (Cycles II and III). Sweet corn (cv. Clockwork) was planted at 66000 seeds ha-1 with 82 cm row spacing. In Cycle I, sweet corn was planted soon after cover crop incorporation, with some seed predation by seedcorn maggot (Delia platura Meigen). Hammond and Cooper (1993) demonstrated that incorporation of green plant materials cues oviposition by this pest and that damage can be reduced by delaying planting until approximately 250 thermal units (3.9°C base) have accumulated. Consequently, sweet corn planting was delayed 10 to 14 d after cover crop destruction and tillage in Cycles II and III, specifically to reduce this problem.
Nitrogen fertilizer (NH4NO3) was applied to sweet corn at 0, 78, and 156 kg N ha-1 within each cover crop system. Applications were made by hand, in a band 5 cm to the side and 5 cm below the seed, after forming a furrow with a narrow hoe. Following application, the furrow was closed. This N application allowed the calculation of FRVs for alfalfa and VR cover crops by comparing yield following legume without N fertilizer to fertilizer N response after winter rye (Hesterman, 1988) and the evaluation of sweet corn N response within each cover crop system. At the appropriate stage of development, all sweet corn ears were harvested by hand from a two row by 3.1 m section in the center of each plot and harvest plant population was measured. Harvested ears were separated into marketable and nonmarketable categories based on size, with a minimum marketable size of 17 cm, and the weight of ears in each category was recorded.
Cover biomass was measured in October and May of each rotation cycle by clipping two 0.1 m2 quadrats plot-1 to ground level and excavating roots from the same area to a depth of 0.3 m. Root material was washed and all plant material was dried (70°C, 3 d) and ground to pass a 2 mm screen. Total N content of plant material was determined by micro-Kjeldahl digestion of 0.25 g sample using sulfuric acid (H2SO4), hydrogen peroxide (H2O2, 30%), and stabilizing salt (K2SO4/CuSO4) in Folin–Wu tubes at 350°C (Wall and Gehrke, 1975). A Lachat Automated Ion Analyzer (Lachat Instruments, Mequon WI) was used to determined NH4–N content in the digest solution (QuikChem Method 12-107-06-2-A, Lachat Instruments).
When corn was 30 to 40 cm tall, fifteen soil cores (2.5 cm diameter by 30 cm deep each) per plot were sampled and composited for PSNT. Samples were taken only from plots that did not receive N fertilizer. Cores from each plot were mixed thoroughly and immediately air dried. A 5 g subsample was extracted for 1 hr in 2 M KCl, and N03–N was determined on a Lachat Automated Ion Analyzer (QuikChem Method 12-107-04-1-B, Lachat Instruments). Data are reported in mg NO3–N kg-1 dry soil. A Minolta SPAD-502 chlorophyll meter (Minolta Corporation, Ramsey NJ) was used to collect leaf chlorophyll measurements, as described by Piekielek and Fox (1992). Measurements were made on the 5th leaf of V-6 stage corn plants, taking the mean of 20 to 25 measurements plot-1.
The experimental design was a randomized complete block with four replications. Treatments were arranged factorially, with the two factors being cover crop and N rate applied to sweet corn. Preliminary analysis of data was accomplished via analysis of variance (ANOVA) with main effects (rotation cycle, cover crop, N rate applied to sweet corn) and interactions. Significant interactions between rotation cycle and treatment (cover crop, N rate) led us to present data for each rotation cycle separately. Cover crop biomass and N accumulation were compared using least significant difference (LSD) only if ANOVA indicated significant treatment differences at 
= 0.05. To further partition cover crop and N rate effects on sweet corn, single degree of freedom contrasts were utilized to evaluate response to N fertilizer rate (N linear, N quadratic), compare cover crops (legume vs. rye, alfalfa vs. VR), and evaluate cover crop by N rate interactions. Regression equations for N rate response were developed only if linear or quadratic contrasts were significant within that cover crop system. Regression equations were calculated using treatment means, as they are intended to describe the general relationship between N rate and crop yield. Following Hesterman et al. (1992), FRVs were calculated for legume cover crops only if sweet corn yield following the legume cover crop was significantly higher than yield following winter rye without N fertilizer.
Main effects (cover crop, N rate) and interactions between main effects were evaluated on three parameters: marketable ear yield ha-1, total ear yield ha-1, and LCNT. Total ear yield was used as an estimate of overall crop productivity. The LCNT is expected to integrate the plant response to both cover crop and fertilizer N sources.
|
Results and discussion
|
|---|
Cover Crop Biomass and N Accumulation
Preliminary ANOVA using a combined dataset (across rotation cycles) indicated significant cycle by cover crop interactions for most cover crop parameters. For this reason, rotation cycles were analyzed separately. Cover crop biomass in the fall was generally quite small [<0.5 Mg dry matter (DM) ha-1; data not shown]. Total cover crop biomass just prior to incorporation in late May ranged from approximately 3.7 to 6.9 Mg DM ha-1 (Table 3)
, demonstrating that these cover crops are well adapted to a moderately cool growing environment. Total biomass for rye and VR was similar to that found in more southern locations, including Maryland (Clark et al., 1994; Shipley et al., 1992), North Carolina (Rannells and Wagger, 1996), and Georgia (McVay et al., 1989). In Cycles I and III, VR produced significantly more above-ground biomass than either alfalfa or rye grown alone. In Cycle II, the proportion of hairy vetch in the mixture was very low (<10% of DM), presumably due to both a later seeding date and harsh winter conditions without prolonged snow cover. As expected, root biomass accumulation by alfalfa was higher than either annual cover crop option (rye, VR).
Cover crop N content (the product of biomass accumulation and tissue N concentration) varied widely, from 52 to 209 kg N ha-1 (Table 4)
. In Cycles I and III, both legume cover crops had higher N content than rye grown alone, generally accumulating two to three times as much N. In these two rotation cycles, the N content of alfalfa and VR were similar, as were above- and below-ground tissue N concentration. The N content we observed for alfalfa (105–174 kg N ha-1) is higher than the 20 to 75 kg N ha-1 found by Hesterman et al. (1992), although they incorporated the alfalfa 3 to 4 wk earlier. Stute and Posner (1995) found that dormant alfalfa accumulated 40 to 50 kg N ha-1 during the seeding year when underseeded with oat, but did not provide estimates for spring regrowth immediately prior to incorporation. Hairy vetch herbage, when grown alone, generally contains 35 to 45 g N kg-1 DM (McVay et al., 1989; Skarphol et al., 1987) and mineralizes very rapidly when incorporated into the soil. Growing this legume in mixture with a small grain generally dilutes tissue N concentration for the herbage as a whole. Even with this dilution effect, VR accumulated as much N as alfalfa and had similar tissue N concentration (Table 4). As mentioned above, hairy vetch growth during Cycle II was very limited, thus tissue N concentration and N content were similar to rye grown alone. Rye is a standard cover crop in many areas because of its winterhardiness and tolerance of late planting. As we found in our research, it can produce a substantial amount of biomass as a winter cover crop, generally from 2.5 to 5.5 Mg DM ha-1 in northern climates (Tollenaar et al., 1993, in Ontario; Kuo et al., 1996, in Washington). However, tissue N concentration is commonly 10 to 15 g kg-1 or less, especially after seedhead emergence, so total N accumulation may be low.
Sweet Corn Response to Cover Crops and N Fertilizer
Sweet corn yield was affected by both cover crop and fertilizer N rate, as shown in Table 5
. Although main effect contrasts (e.g., legume vs. rye) were often significant, interaction contrasts were given precedence. The response of sweet corn in Cycles I and III was very similar in this regard. The legume vs. rye x N linear contrast was significant at = 0.10 for all yield parameters in Cycles I and III and was significant at = 0.05 for three of four yield parameters (total ear yield in Cycle III was the exception). When this contrast is significant, the linear yield response to increasing fertilizer N rate is different for sweet corn following rye than following a legume (either alfalfa or VR). The consistent nature of this interaction for Cycles I and III is shown in Fig. 1 and 2
(top and bottom of each graph, respectively). The regression equations and regression lines are provided only for significant yield responses to fertilizer N, as identified by linear and quadratic orthogonal contrasts within each cover crop system. In each case, sweet corn following rye exhibited a significant linear response to fertilizer N rate, whereas sweet corn following either legume cover crop did not respond to fertilizer N. This differential response to fertilizer N inputs following legumes as cover crops or green manures is common. Tiffin and Hesterman (1998)(corn after red clover), McVay et al. (1989)(corn after wheat or hairy vetch), and Hesterman et al. (1992)(corn after wheat plus underseeded alfalfa or red clover) observed similar responses for field corn. Skarphol et al. (1987)(snap bean after wheat, hairy vetch, or winter pea) and Burket et al. (1987; broccoli or sweet corn after rye and red clover) observed similar responses for vegetable crops.
View this table:
[in this window]
[in a new window]
|
Table 5 Analysis of variance for sweet corn yield and leaf chlorophyll nitrogen test (LCNT) response to cover crop and N fertilizer rate, for three rotation cycles in Stillwater, ME
|
|
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 1 Cover crop and N fertilizer rate effects on marketable (ear length > 17 cm) sweet corn yield by weight for three rotation cycles in Stillwater, ME. Regression equations are provided for N response found to be significant using linear or quadratic orthogonal contrasts and were derived using treatment means at each N fertilizer rate
|
|
View larger version (24K):
[in this window]
[in a new window]
|
Fig. 2 Cover crop and N fertilizer rate effects on total sweet corn yield for three rotation cycles in Stillwater, ME. Regression equations are provided for N response found to be significant using linear or quadratic orthogonal contrasts and were derived using treatment means at each N fertilizer rate
|
|
These data strongly suggest that legume cover crops fulfilled the entire N requirement of the subsequent sweet corn crop in Cycles I and III and that non-N effects from the legumes were minimal. First, as mentioned above, there was no response to fertilizer N after either cover crop. If the legume had supplied only a small portion of the N needed by the sweet corn, yield should have increased with at least the first increment of fertilizer N (78 kg ha-1). Second, a response to fertilizer N also would be expected if the increase in yield following a legume was due at least partially to non-N effects. This type of response, where yield following a legume is higher than following a nonlegume at all N rates, was observed by Hesterman et al. (1986) for corn following alfalfa. Finally, when no fertilizer N was applied, marketable yield following legumes increased an average of 15 to 40% (Cycles III and I, respectively), compared with following rye. It is feasible that the legume cover crops might improve water holding capacity, conductivity, or other parameters that would positively affect plant growth. However, the cover crop biomass incorporated was very similar for legume and nonlegume cover crops, meaning that the legume would have to impact these parameters in a manner different from the effect of rye cover crop.
In Cycle II, the primary response of sweet corn was to N fertilizer; there was no significant cover crop effect and no meaningful interaction (Table 5). Marketable and total yield responses to N fertilizer were quadratic (Fig. 1 and 2, respectively). This response can be generalized across all cover crop systems, as the N quadratic main effect contrast was significant for both marketable and total yield. The lack of cover crop effect in this rotation cycle and the lack of differential response to N fertilizer are probably due to the much smaller biomass and N accumulation by both alfalfa and hairy vetch (in the vetch + rye), as shown in Tables 3 and 4. Although it is common for the relationship between cover crop biomass or N content and the yield of a subsequent nonlegume crop to be moderate to nonexistent (Bruulsema and Christie, 1987; Stute and Posner, 1995), minimal accumulation usually results in either no response or a response very similar to nonlegume cover crop systems. We also considered that low July precipitation (52 mm vs. long-term mean of 85 mm) may have limited sweet corn response to legume N. Although mineralization may have been moisture limited, this seems unlikely to be severe enough to produce this lack of response. Additionally, sweet corn did respond to fertilizer N, indicating that moisture was not limiting for plant growth and development.
Fertilizer Replacement Values of Cover Crops
Fertilizer replacement values were calculated for alfalfa and VR in Cycles I and III. There was no difference in sweet corn yield following legumes or rye in Cycle II when no fertilizer was applied. The FRV was calculated using both of the yield parameters, although this did not greatly influence the results. The FRV for alfalfa and VR ranged from 58 to 156 kg N ha-1 (Table 6) , most often between 80 and 120 kg N ha-1. The FRV for VR was either equal to or greater than the FRV for alfalfa, regardless of which yield parameter was used in the calculation. The ability of these legume cover crops to supply N to a subsequent corn crop is very similar to that found in previous evaluations, including Bruulsema and Christie (1987), Hesterman et al. (1992), and Stute and Posner (1995).
View this table:
[in this window]
[in a new window]
|
Table 6 Fertilizer replacement value (FRV) for alfalfa and vetch + rye cover crops preceding sweet corn in Stillwater, ME
|
|
Presidedress Soil Nitrate Test and Leaf Chlorophyll Nitrogen Test for Sweet Corn
Cover crops significantly affected PSNT in all three rotation cycles (Fig. 3)
when no N fertilizer was applied. In Cycles I and III, PSNT following alfalfa and VR were similar, and were greater than PSNT following rye. In both cycles, the PSNT following alfalfa and VR was above the critical value for sweet corn determined by Heckman et al. (1995). In Cycle II, alfalfa increased PSNT compared with both VR and rye, both of which were slightly below the critical value. Kuo et al. (1996) found that that PSNT reflected the N concentration and content of preceding cover crops and that the legume cover crops like hairy vetch and winter peas resulted in PSNT levels of 25 to 40 mg NO3–N kg-1 soil, similar to those reported here. Utomo et al. (1990) measured soil NO3–N and also showed that hairy vetch increased soil N levels from 0 to 45 cm deep.
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 3 Presidedress soil nitrate concentration in soil following alfalfa, rye, and vetch plus rye cover crops for three rotation cycles in Stillwater, ME
|
|
Expressing our data in the widely used Cate–Nelson format (Fig. 4)
indicates the PSNT was approximately 75% accurate in identifying N responsive sites, slightly lower than the accuracy reported by both Heckman et al. (1995) and Jemison and Lytle (1996). Most of the erroneous points fell into the lower right quadrant, where additional N would not have been recommended but a yield penalty would occur. The accuracy of the LCNT on zero N plots was similar (Fig. 4), using a critical value of 43.5 SPAD units (Jemison and Lytle, 1996). Based on total yield, most erroneous predictions for the LCNT fell into the upper left quadrant where additional N would have been applied (because LCNT was below the critical value) but would not have resulted in a yield increase.
View larger version (24K):
[in this window]
[in a new window]
|
Fig. 4 Relative marketable and total sweet corn yield as a function of presidedress soil nitrate concentration (A and B, respectively) and leaf chlorophyll (SPAD; C and D, respectively). Relative yields equal to observed yield divided by highest treatment mean
|
|
The LCNT also can be used to evaluate overall N status of the plant, as it integrates the plant's response to all N sources. It is clear that cover crop and N rate affect LCNT and yield similarly (Table 5; yields in Fig. 1 and 2). Increasing N rate leads to higher LCNT only following rye cover crop in all rotation cycles (Fig. 5)
. However, LCNT was not affected by N rate following alfalfa or VR, as was generally the case for marketable and total yield. This differential response to fertilizer N, depending on the preceding cover crop, is indicated by the legume vs. rye x N linear contrast (Table 5) and further demonstrates that these legume cover crops can meet or nearly meet the entire N demand for sweet corn in a short-season environment.
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 5 Cover crop and N fertilizer rate effects on leaf chlorophyll for three rotation cycles in Stillwater, ME. Regression equations are provided for N response found to be significant using linear or quadratic orthogonal contrasts and were derived using treatment means at each N fertilizer rate
|
|
|
Conclusions
|
|---|
Sweet corn following alfalfa or VR generally did not respond to additional N fertilizer, as it did following rye grown alone. Alfalfa and VR cover crops supplied all or nearly all of the N required by sweet corn, with FRV ranging from 58 to 156 kg N ha-1. In one rotation cycle (Cycle II), however, severe winter conditions limited survival of both legume cover crops, resulting in no significant N contribution from the legumes. Both the PSNT and LCNT, using previously established critical values of 25 mg kg-1 (Heckman et al., 1995) and 43.5 SPAD units (Jemison and Lytle, 1996), respectively, could identify responsive sites with an accuracy of about 75%.
|
NOTES
|
|---|
Maine Agric. Forest Exp. Stn. Publ. 2367. Partial Funding from USDA-SARE, Project ANE92-31.
Received for publication May 3, 1999.
|
REFERENCES
|
|---|
- Altieri M.A. Agroecology: The science of sustainable agriculture, 2nd Edition Boulder, CO: Westview Press, 1995.
- Biederbeck V.O., Campbell C.A., Rasiah V., Zentner R.P., Wen G. Soil quality attributes as influenced by annual legumes used a green manure. Soil Biol. Biochem. 1998;30:1177-1185.
- Blackmer T.M., Schepers J.S. Use of a chlorophyll meter to monitor nitrogen status and schedule fertigation of corn. J. Prod. Agric. 1995;8:56-60.
- Bruulsema T.W., Christie B.R. Nitrogen contribution to succeeding sweet corn from alfalfa and red clover. Agron. J. 1987;79:96-100.[Abstract/Free Full Text]
- Burket J.Z., Hemphill D.D., Dick R.P. Winter cover crops and nitrogen management in sweet corn and broccoli rotations. HortScience 1997;32:664-668.[Abstract/Free Full Text]
- Clark A.J., Decker A.M., Meisinger J.J. Seeding rate and kill date effects on hairy vetch–cereal rye cover crop mixtures for corn production. Agron. J. 1994;86:1065-1070.[Abstract/Free Full Text]
- Fox R.H., Roth G.W., Iverson K.V., Piekielek W.P. Soil and tissue nitrate tests compared for predicting soil nitrogen availability to corn. Agron. J. 1989;81:971-974.[Abstract/Free Full Text]
- Hammond R.B., Cooper R.L. Interaction of planting times following the incorporation of a living, green cover crop and control measures on seedcorn maggot populations in soybean. Crop Prot. 1993;12:539-543.
- Heckman J.R., Hlubik W.T., Prostak D.J., Paterson J.W. Pre-sidedress soil nitrate test for sweet corn. HortScience 1995;30:1033-1036.[Abstract/Free Full Text]
- Hesterman O.B. Exploiting forage legumes for nitrogen contributions in cropping systems. In: Hargrove W.L., ed. Cropping strategies for efficient use of water and nitrogen. Madison WI: ASA, 1988:155-166 ASA Spec. Publ. 51..
- Hesterman O.B., Griffin T.S., Williams P.T., Harris G.H., Christenson D.R. Forage legume–small grain intercrops: Nitrogen production and response for subsequent corn. J. Prod. Agric. 1992;5:340-348.
- Hesterman O.B., Sheaffer C.C., Barnes D.K., Lueschen W.E., Ford J.H. Alfalfa dry matter and nitrogen production, and fertilizer nitrogen response in legume–corn rotations. Agron. J. 1986;78:19-23.[Abstract/Free Full Text]
- Jemison J.M., Jr., Lytle D.E. Field evaluation of two nitrogen testing methods in Maine. J. Prod. Agric. 1996;9:108-113.
- Kumwenda J.D.T., Radcliffe D.E., Hargrove W.L., Bridges D.C. Reseeding of crimson clover and corn grain yield in a living mulch system. Soil Sci. Soc. Am. J. 1993;57:517-523.[Abstract/Free Full Text]
- Kuo S., Sainju U.M., Jellum E. Winter cover cropping influence on nitrogen mineralization, presidedress soil nitrate test, and corn yields. Biol. Fertil. Soils 1996;22:310-317.
- Magdoff F.R., Ross D., Amadon J. A soil test for nitrogen availability to corn. Soil Sci. Soc. Am. J. 1984;48:1301-1304.[Abstract/Free Full Text]
- McVay K.A., Radcliffe D.E., Hargrove W.L. Winter legume effects on soil properties and nitrogen fertilizer requirements. Soil Sci. Soc. Am. J. 1989;53:1856-1862.[Abstract/Free Full Text]
- Piekielek W.P., Fox R.H. Use of a chlorophyll meter to predict sidedress N requirements for maize. Agron. J. 1992;84:59-65.[Abstract/Free Full Text]
- Rannells N.N., Wagger M.G. Nitrogen release from grass and legume cover crop monocultures and bicultures. Agron. J. 1996;88:777-782.[Abstract/Free Full Text]
- Shipley P.R., Meisinger J.J., Decker A.M. Conserving residual corn fertilizer nitrogen with winter cover crops. Agron. J. 1992;84:869-876.[Abstract/Free Full Text]
- Skarphol B.J., Corey K.A., Meisinger J.J. Response of snap beans to tillage and cover crops. J. Am. Soc. Hortic. Sci. 1987;112:936-941.
- Stivers L.J., Sheehan C. Meeting the nitrogen need of processing tomatoes through winter cover cropping. J. Prod. Agric. 1991;4:330-335.
- Stute J.K., Posner J.L. Legume cover crops as a nitrogen source for corn in an oat–corn rotation. J. Prod. Agric. 1995;8:385-390.
- Tiffin P., Hesterman O.B. Response of corn grain yield to early and late killed red clover green manure and subirrigation. J. Prod. Agric. 1998;11:112-121.
- Tollenaar M., Mihajlovic M., Vyn T.J. Corn growth following cover crops: Influence of cereal cultivar, cereal removal, and nitrogen rate. Agron. J. 1993;85:251-255.[Abstract/Free Full Text]
- Utomo M., Frye W.W., Bevins R.L. Sustaining soil nitrogen for corn using hairy vetch cover crop. Agron. J. 1990;82:979-983.[Abstract/Free Full Text]
- Wall L.L., Gehrke C.W. An automated total protein nitrogen method. J. Assoc. Off. Anal. Chem. 1975;58:1221-1226.
This article has been cited by other articles:
|
|
|
|
 
L. Zotarelli, L. Avila, J. M. S. Scholberg, and B. J. R. Alves
Benefits of Vetch and Rye Cover Crops to Sweet Corn under No-Tillage
Agron. J.,
February 4, 2009;
101(2):
252 - 260.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Sharifi, B. J. Zebarth, D. L. Burton, C. A. Grant, and G. A. Porter
Organic Amendment History and Crop Rotation Effects on Soil Nitrogen Mineralization Potential and Soil Nitrogen Supply in a Potato Cropping System
Agron. J.,
October 21, 2008;
100(6):
1562 - 1572.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. M. Cherr, J. M. S. Scholberg, and R. McSorley
Green Manure as Nitrogen Source for Sweet Corn in a Warm-Temperate Environment
Agron. J.,
August 3, 2006;
98(5):
1173 - 1180.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. M. Cherr, J. M. S. Scholberg, and R. McSorley
Green Manure Approaches to Crop Production: A Synthesis
Agron. J.,
February 7, 2006;
98(2):
302 - 319.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. L. Weinert, W. L. Pan, M. R. Moneymaker, G. S. Santo, and R. G. Stevens
Nitrogen Recycling by Nonleguminous Winter Cover Crops to Reduce Leaching in Potato Rotations
Agron. J.,
March 1, 2002;
94(2):
365 - 372.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. E. Blackshaw, J. R. Moyer, R. C. Doram, A.L. Boswall, and E. G. Smith
Suitability of Undersown Sweetclover as a Fallow Replacement in Semiarid Cropping Systems
Agron. J.,
July 1, 2001;
93(4):
863 - 868.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. J.O. Odhiambo and A. A. Bomke
Grass and Legume Cover Crop Effects on Dry Matter and Nitrogen Accumulation
Agron. J.,
March 1, 2001;
93(2):
299 - 307.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
