By M.L. Ruffo and G.A. Bollero, University of Illinois.

Introduction:

• Winter cover crops (WCC) are used for nutrient management and soil conservation purposes in Eastern and South-Eastern US (Reeves, 1994).
• There is a lack information about the benefits and effects of WCC on corn (Zea mays L.) production systems in the Central Corn Belt.
• Rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) are the preferred WCC in the Central Corn Belt (Reeves, 1994). Their mixture is another alternative which provides the benefits of both species.
• Winter cover crops affect soil nitrogen (N) cycle (mineralization-immobilization turnover and denitrification) and consequently the soil mineral N availability (McKenney et al., 1995).
• Winter cover crops have shown positive, neutral, or negative effects on corn yield, depending on their management and the environmental conditions during the growing season (Bollero and Bullock, 1994; Clark et al., 1997).
• The effect of winter cover crops on corn yield has been attributed mainly to soil mineral N availability.
• In corn cropping systems that include WCC the synchrony between corn N demand and N supply is critical to increase grain yield (Myers et al., 1997).

Objectives:

• Analyze the effect of hairy vetch, rye and their biculture on the dynamics of corn N content and soil mineral N.
• Analyze the response of corn yield to hairy vetch, rye and their biculture.

Materials and Methods:

Field experiments were conducted on 1999 and 2000 at Brownstown and Urbana IL. In Brownstown the soil is a Cisne silt loam (Vertic albaqualf; 0.77% Total C, pH 6.3) and in Urbana a Drummer silty clay loam (Typic endoaquoll; 1.37% Total C, pH 6.2).

The experiment was a completely randomized block design with four replications. Plot dimensions were 4.2 m (6, 70 cm-rows) wide by 10 m long. The experiment was conducted under no-till in plots that have previously been in corn-soybean rotation for at least 5 years.

Winter cover crop systems consisted on three treatments (rye, hairy vetch, a biculture of these two species), and a control (winter fallow). Seeding rate was 134 kg ha^-1 and 34 kg ha^-1 for monoculture rye and hairy vetch, respectively. The seeding rate in the biculture was 67 kg ha^-1 for rye and 22.5 kg ha^-1 for hairy vetch.

Cover crops were drilled on soybean stubble every year. Hairy vetch was inoculated with Rhizobium viciae. In the following spring, cover crops were desiccated with glyphosate.

Winter cover crops dry matter at desiccation was estimated sampling an area of 0.4 m². Rye and hairy vetch were separated in the biculture. Plant material was dried, weighed and analyzed for total N concentration. Winter cover crops nitrogen content was calculated as the product of biomass and N concentration.

Corn dry matter was estimated by cutting 5 plants per plot at V₆ and 3 plants per plot at R₁ and harvest. The plants were analyzed for total N concentration. Corn nitrogen content was calculated as the product of biomass and N concentration. Corn yield was estimated by harvesting the two central rows with a plot combine. Yield is presented on a 155 g kg^-1 moisture basis.

Soil was sampled to a depth of 0.3m at corn planting,V₆, R₁, and at harvest. Samples were dried and analyzed for and N-NO3^-. Soil mineral N-NO3^- content was calculated considering a bulk density of 1.38 g cm^-3. Data was analyzed using SAS PROC MIXED. Locations and WCC were considered fixed effects and year a random effect. Means were separated with LSMEANS.

Results and Discussion:

A summary of the ANOVA results for the analyzed variables is presented in Table 1 and Table 2. Only significant effects are shown. Means for WCC are presented in Fig. 1 for WCC N content, in Fig. 2 for corn yield, and in Figs. 3, 4, 5, and 6 for soil N-NO3^- content, corn N content and soil + corn N content at planting, V₆, R₁, and harvest, respectively.

Table 1.

Significant effects and associated p value for winter cover crops N content and corn grain yield.

Table 2.

Significant effects and associated p values for soil N-NO3^-, corn N content and soil N+ corn N at planting, V₆, R₁, and harvest.

• The inclusion of hairy vetch in the biculture did not increase total N content of the biculture (Fig. 1).
• The large N content of rye suggests that there was a large pool of nitrates at WCC drilling time and that rye was able to capture at least a significant part of it.
• At V₆ (Fig. 4) hairy vetch presented more N in the soil-crop system than rye and the rye/hairy vetch biculture, probably due to immobilization caused by rye residues. The immobilization of mineral N reduced corn N content. Soil N-NO3^- content was larger at Urbana (1.72 g N m^-2) than at Brownstown (1.04 g N m^-2), reflecting the differences in soil organic matter concentration between these locations. At R₁ (Fig. 5) soil-crop system differences disappeared probably due to the mineralization of soil organic N and some residue N mineralization. Corn N content was larger after hairy vetch than after fallow, indicating a good synchrony between hairy vetch residue N mineralization and corn uptake. At harvest (Fig. 6) soil-crop N was not different between fallow and hairy vetch indicating similar total N supply in both treatments.
• Winter cover crops had a highly significant effect on corn grain yield (p<0.001). Hairy vetch significantly increased corn grain yield compared to the fallow treatment (Fig. 2), probably as a consequence of the larger corn N content at R₁ after hairy vetch (Fig. 5). In agreement with several reports (Wagger, 1989; Bollero and Bullock, 1994), rye reduced corn yield compared to winter fallow (Fig. 2). We believe that this yield reduction was due to N deficiency caused by N immobilization rather than other reported deleterious effects of rye, like allelopathy or reduced stands (Tollenaar et al., 1993; Eckert, 1988). The analysis of the location x winter cover crop interaction (p<0.1) showed that at Brownstown, corn grain yield was larger after hairy vetch (615 g m^-2) than after fallow (489 g m^-2) and that after rye (391 g m^-2) corn grain yield was not significantly lower than fallow. On the other hand, at Urbana, hairy vetch (748 g m^-2) did not increase corn grain yield compared to fallow (639 g m^-2), but rye (296 g m^-2) reduced corn grain yield.

Conclusions:

• Hairy vetch increased corn grain yield mainly by a timely supply of N rather than by increasing final N availability.
• Rye, either alone or in biculture with hairy vetch, immobilized N and consequently reduced corn grain yield.
• In Central and Southern Illinois, rye seems to be a suitable cash crop while hairy vetch supplies N at critical time increasing grain yield.

References:

• Bollero, G. A., and D. G. Bullock. 1994. Cover cropping systems for the central corn belt. J. Prod. Agric. 7: 55-58.
• Clark, A. J., A. M. Decker, J. J. Meisinger, and M. S. McIntosh. 1997b. Kill date of vetch, rye, and a vetch-rye mixture:II. Soil moisture and corn yield. Agron. J. 89: 434-441.
• Eckert, D. J. 1988. Rye cover crops for no-tillage corn and soybean production. J. Prod. Agric. 1: 207-210.
• McKenney, D.J., S.W. Wang, C.F. Drury, and W.F. Findlay. 1995. Denitrification, immobilization and mineralization in nitrate imited and non limited residue-amended soil. Soil Sci. Soc. Am. J. 59:118-124.
• Myers, R.J.K., M. van Noordwijk and P. Vityakon. Synchrony of nutrient release and plant demand: Plant litter quality, soil environment and farmer manegement options. In G. Cadisch and K. Giller (ed.). Driven by nature: plant litter quality and decomposition. CAB International.
• Reeves, D.W. 1994. Cover crops and rotations. p. 125-172. In J.L. Hatfield and B.A. Stewart (ed.) Crops Residue Management. CRC Press, Inc. FL.
• Tollenaar, M., M. Mihajlovic and T.J. Vyn. 1993. Corn growth following cover crops: influence of cereal cultivar, cereal removal and nitrogen rate. Agron. J. 85:251-255.
• Wagger, M.G. 1989. Cover crop management and nitrogen rate in relation to growth and yield of no-till corn. Agron. J. 81:533-538.