Grain Yield of Oat-Pea Intercrop

1. METHODOLOGY
2. RESULTS
3. CONCLUSION
4. REFERENCES
5. Table 1
6. Table 2

Spring oat (Avena sativa L., Poaceae) is grown for both forage and grain in temperate regions at upper latitudes. Oat is sometimes intercropped with spring pea (Pisum sativum L.) to enhance forage quality. Oat-pea mixtures have been considered for grain and seed production, though not to the extent as for forage. Generally, total grain yield has not been increased by intercropping (Carter and Larson 1964; Cowell et al. 1988).

Oat-pea intercrops have been established by sowing both crops at rates less than those used when sole-cropping either crop. This investigation was conducted to determine how grain yield of oat-pea mixtures was affected by sowing oat and pea components at or above the sole-cropped rate in North Dakota, U.S.

METHODOLOGY

A field experiment was conducted at Dickinson (46°53' N, 102°49' W) in southwestern North Dakota under dryland management during the 1993 and 1994 growing seasons, and at Hettinger (46°00' N, 102°30' W) under dryland management during the 1993 growing season. Average daily temperature ranges from -10°C during the winter (Dec. 1 to Feb. 19) to 19°C during the summer (June 1 to Aug. 31) at Dickinson, and -9° to 20°C at Hettinger. Precipitation averages 422 mm annually at Dickinson and 407 mm at Hettinger, with slightly less than two-thirds occurring between Apr. 1 and July 31.

The experiment was established in a seedbed that had been fallowed the previous year at Dickinson in 1993 and 1994, and at Hettinger in 1993. The seedbed was prepared by disking and then firming with a field cultivator and harrow. The experiment was also established in an annually-cropped, no-tillage seedbed at Dickinson in both years.

'Dumont' oat was sown alone and mixed with 'Trapper' field pea on Apr. 29 at Dickinson and Apr. 22 at Hettinger in 1993, and May 2 at Dickinson in 1994. 'Dumont' is grown for both grain and forage and is a popular oat cultivar in the northern Great Plains region of North America. 'Trapper' is a small sized pea that is suited to intercropping with oat (Chapko et al. 1991).

Oat was sown at 185 kernels/m² (pure live seed) in sole-crops at Dickinson in 1993, and at 93, 185, and 278 kernels/m² in 1994. Oat was sown at 99, 198, and 297 kernels/m² at Hettinger in 1993. Pea was sown at 80 seeds/m² (pure live seed) in sole-crops at Dickinson and Hettinger in both years, and also at 40 and 120 seeds/m² at Hettinger in 1993 and at Dickinson in 1994. Oat was intercropped with pea at all sole-crop rates used at each location in 1993 and 1994.

A randomized complete-block design was used at all locations. Blocks were replicated four times. Plot dimensions were 1.8 by 8 m at Dickinson and 1.6 by 8.5 m at Hettinger.

Yield was determined by collecting mixed grain and seed with a research combine. Grain and seed samples were cleaned and dried at 60°C for 48 to 72 h and weighed. Split pea seed could not be separated from oat kernels in oat-pea mixtures, so a 200 g subsample was collected from each intercropped sample and separated by hand so crop composition of the grain mixture could be estimated.

The land equivalent ratio (LER) index was used to evaluate intercrop efficiencies with respect to sole-crops. The LER defines yield as a function of area (LER = Io/So + Ip/Sp) where I and S refer to intercrop and sole-crop yields, respectively, and the subscripts o and p indicate the oat and pea component crops in the mixture.

Data were analyzed for each location but not across years or environments because some sole-cropped treatments were included in 1994 but not in 1993 at Dickinson. In addition, the recommended sole-crop rate for oat differed between Dickinson and Hettinger.

RESULTS

Yield was similar between intercrop treatments and sole-crop oat treatments where oat was sown at the recommended rate at each location (Table 1). More grain and seed generally was produced by some intercrop treatments than seed by a sole-crop of pea. These data indicate that intercropping may not reduce total yield compared with a monoculture of oat if oat is sown at the sole-crop rate or a heavier rate in the mixture. Total yield can be increased by intercropping compared with a sole-crop of pea.

More of the mixed grain and seed was oat as the oat seeding rate was increased and the pea seeding rate was decreased (Table 2). Pea composed more of the mixed grain and seed as the pea seeding rate was increased and the seeding rate for oat was reduced. No intercrop treatment in this investigation produced mixed grain that was comprised of equal proportions of oat and pea at all locations. However, roughly equal proportions of oat groats and pea was produced at Dickinson across environments and years when oat was sown at half the sole-crop rate and pea at the sole-crop rate.

The LER suggested a potential advantage for intercropping in both environments at Dickinson in 1993, and for some intercrop treatments in the fallowed environment in 1994 (Table 1). An advantage for intercropping was not suggested by LERs of intercropped treatments at Hettinger in 1993 and in the annually-cropped environment at Dickinson in 1994. The largest LER value for an intercrop treatment across locations and years occurred when both oat and pea were sown at rates heavier than those recommended for a sole-crop.

CONCLUSION

Total yield generally was maintained or enhanced when oat was intercropped at a sole-crop rate with pea compared to growing oat alone in this investigation. Previous work indicates that crude protein content is increased by intercropping oat with pea compared with growing oat alone (Robinson 1960; Johnston et al. 1978). Since total yield can be maintained when intercropping oat and pea, we suggest that oat-pea mixtures are a higher N-grain alternative to a monoculture of oat, and should be considered if the mixed grain is grown for direct consumption by livestock.

REFERENCES

Carter, J.F. and K.L. Larson. 1964. Oats, peas, and vetch for hay or silage in North Dakota. North Dakota Ag. Expt. Sta. Fargo. Bul. 14 Agr. 9-5.