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Field Crops Research 179 (2015) 113–119

Contents lists available at ScienceDirect

Field Crops Research

jou rn al hom epage: www.elsev ier .com/ locate / fc r

itrogen uptake, use and utilization efficiency by oat–pea intercrops

einhard W. Neugschwandtner ∗, Hans-Peter Kaulivision of Agronomy, Department of Crop Sciences, University of Natural Resources and Life Sciences Vienna (BOKU), Konrad Lorenz-Straße 24, 3430 Tulln,ustria

r t i c l e i n f o

rticle history:eceived 15 January 2015eceived in revised form 26 April 2015ccepted 27 April 2015

eywords:ntercroppingatea

yield

a b s t r a c t

Cereal–legume intercropping in sustainable arable farming systems in temperate regions is of increasinginterest for increasing productivity. This study assessed the influence of sowing ratio and N fertilizationon nitrogen uptake, use and utilization efficiency of oat (Avena sativa L.) and pea (Pisum sativum L.) inintercrops. A two-year field study was carried out in eastern Austria with oat and pea sown in threesubstitutive sowing ratios and at different nitrogen levels.

Oat was the dominant partner in the mixtures strongly outcompeting pea. Total grain yields weregenerally lower in intercrops than in pure stands. Consequently, nitrogen use and the partial factornitrogen use efficiency for grain production were lower in intercrops. Nitrogen utilization efficiency washighest in pure oat stands and decreased with higher pea shares.

use utilization

Grain N concentration of oat and pea increased with N fertilization. In intercrops, grain N concentrationsof oat increased with lower oat share whereas those of pea were not affected by cropping system. Dueto higher grain N concentrations of oat in intercrops, intercrops could attain a higher grain N yield inunfertilized treatments. Thus, growing oat–pea intercrops can be reasonable for producing grain feed atlow N input level.

. Introduction

Intercropping is a traditional farming technique, which is impor-ant in farming systems of developing countries but far lessidespread in mechanized systems (Lithourgidis et al., 2011). But

here is an increased scientific interest in intercropping systemsn temperate regions for developing sustainable farming systemsor forage (Anil et al., 1998) or grain production (Neugschwandtnernd Kaul, 2014; Zajac et al., 2013, 2014). Yields of grain legumesre generally more variable than those of many other crop speciesJeuffroy and Ney, 1997). Thus, Jensen (1996) has shown that inter-ropping barley with pea resulted in a higher yield stability ofntercrops than of pea pure stands. Yield and yield componentsNeugschwandtner and Kaul, 2014) and yield per plant (Echartet al., 2011) as well as concentrations and uptake of nutrientsLi et al., 2001) of individual crops may be affected in inter-rops compared to pure stands. Higher yields can be obtained

y intercropping through an improved water and radiation cap-ure as shown for maize–soybean intercrops compared to soybeanole cropping (Coll et al., 2012). Thereby, intercropping can be an

∗ Corresponding author. Tel.: +43 1 47654 3311; fax: +43 1 47654 3342.E-mail address: reinhard.neugschwandtner@boku.ac.at

R.W. Neugschwandtner).

ttp://dx.doi.org/10.1016/j.fcr.2015.04.018378-4290/© 2015 Elsevier B.V. All rights reserved.

© 2015 Elsevier B.V. All rights reserved.

alternative under rainfed conditions for reducing farm risk(Monzon et al., 2014). Further one, biological and chemicalsoil characteristics are positively influenced by intercropping(Oelbermann and Echarte, 2011); e.g. intercropping contributes tothe long-term immobilization of N compared to sole cropping asshown for maize–soybean intercrops and, thus, could help to curbthe currently growing reliance on N fertilizers (Regehr et al., 2015).

Cereal–legume intercrops may allow for the optimal use of soiland atmospheric nitrogen sources to maintain high production andquality levels with low fertilizer N inputs to minimize potentialenvironmental impacts, which may occur in intensive agriculturalsystems (Pelzer et al., 2012). Soil inorganic and atmospheric Nsources can be complementarily used by the intercrop compo-nents. Cereals are more competitive than legumes for inorganicsoil N (Jensen, 1996) due to a faster and deeper root growth of thecereal (Corre-Hellou and Crozat, 2005). In substitutive cereal–peaintercrops, the cereal has an even better access to soil N than inpure stands due to a lower plant density but at a similar amountof available N per unit area (Bedoussac and Justes, 2010). Legumessave the soil N pool due to their symbiotic N2 fixation (Chalk et al.,1993; Hauggaard-Nielsen et al., 2001). The portion of N derived

through fixation by pea is further increased in intercrops as thehigher soil mineral N acquisition of the cereal fosters symbioticN2 fixation due to low NO3 concentrations; symbiotic N2 fixation isnegatively affected by that chemical compound (Corre-Hellou et al.,

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006; Hauggaard-Nielsen et al., 2009). Thus, the share of symbioti-ally fixed N in relation to the N uptake of the legume in intercropsan be increased due to competition for soil mineral N by the non-egume, especially with low N fertilization (as shown in barley–peantercrops by Andersen et al., 2005). Nevertheless, the total amountf fixed nitrogen per unit area is often lower in intercrops than inure legume stands due to lower plant density of the legume andompetition by the non-legume accompanying plant (Van Kesselnd Hartley, 2000).

Intercropping is mostly practiced under low soil fertility and lownput conditions (Vesterager et al., 2008); under these conditionsntercropping shows the highest yield increase compared to puretands (Ofori and Stern, 1986; Hauggaard-Nielsen et al., 2009) dueo the high level of complementary N use between the two speciesompared with highly fertilized systems (Bedoussac and Justes,011). Thus, nitrogen fertilization is a critical topic in intercrop-ing. The reliance on soil mineral N for achieving a high grain yield

s different for the partners in cereal–legume intercrops with a highemand for cereals and a low demand for legumes (Cochran andchlentner, 1995). Nitrogen fixation is considerably reduced with

high rate of nitrogen fertilization (Jensen, 1986). The inhibitoryffect of N fertilization on nodulation and N2 fixation of legumesn intensive farming systems can be alleviated by intercroppingon-legume partner (as shown in faba bean/maize intercrops by Lit al., 2009). Several studies have highlighted that N fertilizationf cereal–legume intercrops affects competition between crops,ield and nitrogen yield of individual crops and of the total systemGhaley et al., 2005; Naudin et al., 2010; Pelzer et al., 2012).

The aim of this study were to assess oat–pea intercrops grown on fertile soil in temperate conditions of eastern Austria as affectedy sowing ratio and N fertilization with focus on (a) nitrogen yieldnd (b) nitrogen use and utilization efficiency of oat–pea intercrop-ing systems as compared to pure stands of both crops.

. Material and methods

.1. Experimental site and environmental conditions

The experiment was carried out in Raasdorf (48◦14′ N, 16◦33′ E)n eastern Austria on the experimental farm Gross-Enzersdorf ofOKU University in the years 2010 and 2011. The soil is classifieds a chernozem of alluvial origin and rich in calcareous sedimentspH 7.6, silty loam, 2.2–2.3% organic substance). The mean annualemperature is 10.6 ◦C, the mean annual precipitation is 538 mm1980–2009). The temperature in both growing seasons was gen-rally above the long-term average with higher temperatures in011 than in 2010 (except for July). Monthly precipitation in 2010as highly above average during the growing season from Aprilntil July whereas the vegetation period 2011 was comparativelyry. For detailed information on weather data during the growingeasons see Neugschwandtner and Kaul (2014).

.2. Experimental treatments and measurements

Pure stands of oat (cv. Effektiv) and pea (cv. Lessna, semi-eafless) were established with 350 (oat) and 80 (pea) germinableeeds m−2, respectively. Three substitutive oat–pea intercroppingixtures consisted of the following sowing ratios (oat:pea, based

n the pure stands of each crop in %): 75:25, 50:50 and 25:75. Theitrogen fertilizer calcium ammonium nitrate (CAN, 27% N) was

pplied at two fertilization levels (6 and 12 g N m−2) complementedy an unfertilized control. Fertilizer was applied in two equal splits,ight after sowing and at end of tillering of oat, on May 2, 2010, andn May 5, 2011.

rops Research 179 (2015) 113–119

The preceding crops were winter barley (2010) or spring bar-ley (2011). Seedbed preparation was done with a tine cultivatorto a depth of 20 cm. Sowing of both crops was performed simulta-neously in one pass-over with an Oyjard plot drill at a depth of 4 cmon March 19, 2010, and on March 14, 2011. Individual plots had anarea of 15 m2 (10 × 1.5 m) and comprised 10 rows at 12.5 cm spac-ing. Soil mineral N in 0–0.9 m depth at sowing was 15.8 (March24, 2010) or 16.8 (March 16, 2011) g N m−2 (at 0–0.9 m depth).Mechanical hand weeding was performed throughout the exper-iment; plants were sprayed against pests when necessary [withthe insecticide deltamethrin, 7.5 g a.i. ha−1 (Decis®)]. Plants wereharvested manually by cutting on the soil surface at full ripenesson 1.2 m2 per plot on July 21, 2010, and on July 19, 2011, and driedat 70 ◦C for 3 d. Thereafter, plant samples were divided into grainand residue.

For nitrogen determination, grain and residue samples were firstground to pass through a 1 mm sieve. Nitrogen concentrations weredetermined as average of duplicate samples of about 50 mg eachby the Dumas combustion method (Winkler et al., 2000) using anelemental analyzer (vario MACRO cube CNS; Elementar Analysen-systeme GmbH, Germany).

Grain and residue N yield were calculated by multiplying yieldfigures with N concentrations and from these the N harvest index(NHI) was derived. N use efficiency (NUE), partial factor N use effi-ciency (PFNUE) and N utilization efficiency (NUtE) were calculatedaccording to Sinebo et al. (2004) and Anbessa and Juskiw (2012) asfollows:

NUE (g g−1) = YLD

NMIN + Nf(1)

PFNUE (g g−1) = YLDf

Nf(2)

NUtE (g g−1) = YLD

NYAGDM(3)

where YLD is the grain yield and NYAGDM the nitrogen yield of theabove-ground dry matter; NMIN represents soil mineral N at sowingand Nf the fertilizer level; the subscript f stands for fertilizer N.

The land equivalent ratio for nitrogen yield (LERN), which indi-cates a possible N yield advantage of intercrops, was calculatedmodified according to Mead and Wiley (1980) as follows:

LERN = NYOic/NYOps + NYPic/NYPps (4)

where NYOps and NYPps are the crop N yields for oat (O) and pea(P) grown in pure stands (ps) and NYOic and NYPic are the yieldsof the crops grown in intercrops (ic). A LERN >1 shows an N yieldadvantage of the intercropping system whereas a LERN <1 indicatesan N yield disadvantage. The LERN is the sum of the partial LERN ofthe individual crops in the mixture. The partial LERN indicates therelative competitive ability of individual crops regarding N yieldsin mixtures.

2.3. Statistics

The experiments were in a randomized complete block designwith three replications. Statistical analyses were performed usingSAS version 9.2. Analysis of variance (PROC GLM) with subse-quent multiple comparisons of means were performed. Meanswere separated by least significant differences (LSD), when the F-test indicated factorial effects on the significance level of p < 0.05.

Based on analysis of variance results, data are mainly presented forN fertilization (main effect) and interactions of crop × year. Otherinteractions are presented occasionally in case they were signifi-cant and relevant.

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. Results

.1. Grain and residue yield

The effects of sowing ratio and N fertilization on grain andesidue yields of oat–pea intercrops and the harvest index (HI) ofat and pea have been described in Neugschwandtner and Kaul2014). Briefly, N fertilization significantly increased grain andesidue yields of oat but had no effect on these parameters of pea.at was the dominant partner in the mixtures strongly outcom-eting pea. Decreasing sowing ratios resulted in lower yields ofoth crops. Grain and residue yields of oat slightly decreased withecreasing share in the intercrops whereas pea yields were stronglyffected. The HI of pea was reduced by fertilization whereas that ofat was not affected by fertilization. Intercropping resulted in aecrease of the HI of both crops.

.2. N concentration, N yield and N harvest index of oat and pea

The grain N concentrations of oat increased with both fertil-zation treatments (from 2.05 to 2.40%, i.e. up by one sixth in the2 g N m−2 treatment compared to the control), that of pea with theighest N treatment (3.82% compared to 3.67% in the control, meansver two years). The residue N concentrations of both crops wereore strongly affected by fertilization than the grain N concentra-

ion. The application of the highest N dose increased the residue Noncentration of oat by three quarters and that of pea by one eighthoat: to 0.98%, pea: to 1.42%, both compared to the control, meansver two years) (Fig. 1a and d).

A decreasing share of oat in the sowing ratio increased the grain concentration (from 2.14% (pure oat) to 2.25% (with 25% oat),eans over two years), whereas grain N of pea was not affected by

owing ratio (Fig. 1b and c). The sowing ratio × fertilization inter-ction shows that oat could achieve higher grain N concentrationsn the unfertilized treatments of intercrops with a lower oat shareFig. 2a); thereby the differences to the grain N concentrations of theertilized treatments were reduced. The residue N concentrationsf oat were higher with a decreasing oat share (pure oat: 0.64%,5% oat share: 0.87%, means over two years) and higher in 2010ompared to 2011 (Fig. 1e). The residue N concentration of pea wasigher in the intercrops than in the pure pea stands in 2010; in011, a slightly, although not significant, higher residue N concen-ration occurred in the 25:75 oat–pea mixture than in the otherreatments (Fig. 1f).

Grain and residue N yields of oat were increased by fertiliza-ion whereas those of pea were not affected (Figs. 1g, j). Decreasinghares in intercrops generally reduced the grain N yields of bothrops. The grain N yields of oat slightly dropped with decreasinghare in the intercrops as the oat grain yields also slightly decreasedhile N concentrations increased with a lower sowing density of

at in the intercrops. E.g. in the 50:50 oat:pea intercrops, the grain yields of oat was 22% (2010) or 20% (2011) lower than in theorresponding pure stands (Fig. 1h). In contrast, the pea grain Nields were strongly affected as grain yields have been stronglyeduced due to intercropping (Fig. 1i). The differences in N grainields of oat among N fertilization treatments were higher withigher oat shares (Fig. 2b). As oat residue yields increased slightlynd N concentrations even more strongly with a reduction of oat inhe mixtures, the residue N yields of oat were higher in the inter-rops than in the corresponding pure stands in 2010 and only in theixture with the lowest oat share it was lower than in the other

reatments in 2011 (Fig. 1k). In contrast, pea N yields decreased

harply with lower pea shares in the mixtures (Fig. 1l).

The nitrogen harvest indices (NHI) of both crops were reducedith increasing N fertilization (Fig. 1m). Both crops had generallyigher NHI in the drier year 2011 and lower NHI with a decreasing

rops Research 179 (2015) 113–119 115

share of the crops in the mixtures (Fig. 1n and o). The NHI of oatwas lower in the highest N fertilization treatment in the intercropsbut not reduced in oat pure stands (Fig. 2c).

3.3. Total grain and nitrogen yield, land equivalent ratio of Nyields (LERN)

The total grain yields and total grain N yields increased with fer-tilization. The total grain yields were highest in the pea pure standsand lowest in the intercrops with 25% oat and 75% pea while otherintercrops showed intermediate values. The total grain N yieldswere highest in the pea pure stands where it was 1.88-fold higherthan in the oat pure stands. For intercrops, only the grain N yields ofthe intercrops with 25% oat and 75% pea were significantly higherthan that of the oat pure stands (1.13-fold) (Table 1).

The LER of grain and residue yields and the partial oat grain LERare described in Neugschwandtner and Kaul (2014); also presentedin Table 1. Briefly, the LER of grain yields were below unity (indicat-ing a lower grain productivity of the intercrops) and decreased withfertilization whereas the LER of residue yields were above unity.LERN of grain yields was only in the unfertilized intercrops aboveunity indicating a N yield increase (by 6%) over the pure crop stands.Regarding sowing ratios, the LERN of grain yields were below unitywith a decreasing trend with reducing oat share. In contrast, theLERN of residue were considerably above unity in all fertilizationtreatments with N yield increases of 18–27% in the intercrops. Boththe partial LER and the partial LERN of oat grain were higher in allintercrops than those of pea grain (with generally higher values forthe partial grain LERN than the partial grain LER for oat), indicatingthat oat was the dominant crop in the mixtures. Partial LERN of oatgrain was reduced by the highest N fertilization treatment and thatof pea by both N fertilization treatments (Table 1).

3.4. Nitrogen use and utilization efficiency

The nitrogen use efficiency (NUE), partial nitrogen use efficiency(PFNUE) and the nitrogen utilization efficiency (NUtE) of both cropswere reduced with increasing N fertilization. The decrease was32% (NUE) and 27% (NUtE) for oat and 44% (NUE) and 12% (NUtE)for pea with 12 g m−2 compared to the control (Fig. 3a, f, k). Cor-respondingly, NUE, PNFNUE and NUtE of the total grain yields(oat + pea) dropped with fertilizer N (Fig. 3d, i, n). All three param-eters decreased for both oat and pea with a decreasing share of thecrop in the mixtures, e.g. with a share of 25% in the intercrops, thedecrease was 46% (NUE) and 23% (NUtE) for oat (Fig. 3b, g, l) and95% (NUE and PFNUE) and 21% (NUtE) for pea, respectively, com-pared to the corresponding pure stands (Fig. 3c, h, m; means overtwo years).

For the total grain yields (oat + pea), NUE, PFNUE and NUtE werelower with higher N fertilization. The NUE was highest for pea purestands followed by oat pure stands and lowest for 25:75 oat:peaintercrops (Fig. 3e). The PFNUE was highest for pea pure stands,again followed by oat pure stands, and lowest for the 25:75 and50:50 oat:pea intercrops (Fig. 3j). NUtE was highest for oat purestands, decreased with declining oat shares and was lowest for thepea pure stands (Fig. 3o).

4. Discussion

The higher grain N concentrations of oat in mixtures with loweroat share can be explained by the higher availability of soil min-eral N per unit area for individual oat plants (Kübler et al., 2008;

Bedoussac and Justes, 2010). Also Naudin et al. (2010) reportedsimilar grain N concentrations in unfertilized intercropped and fer-tilized monocropped wheat. The grain N concentration of pea ishighly variable (Lhuillier-Soundélé et al., 1999) and affected by

116 R.W. Neugschwandtner, H.-P. Kaul / Field Crops Research 179 (2015) 113–119

Fig. 1. (a–c) Grain and (d–f) residue N concentration (%), (g–i) grain N and (j–l) residue N yield (g N m−2) and (m–o) nitrogen harvest index (%) of oat and pea depending on Nfertilization (main effect) and sowing ratio × year (interaction). Different letters indicate significant differences, error bars are LSD (p < 0.05). Effects are significant at p < 0.05(*) and p < 0.001 (***). SR = sowing ratio, Y = year.

Fig. 2. (a) Grain N concentration, (b) grain N yield (g N m−2) and (c) N harvest index of oat depending on sowing ratio × N fertilization. Error bars are LSD (p < 0.05).

R.W. Neugschwandtner, H.-P. Kaul / Field Crops Research 179 (2015) 113–119 117

Table 1Land equivalent ratio for grain (LER) and nitrogen yield (LERN) of oat–pea intercrops as affected by intercropping ratio (%), N fertilizer level and year.

Yield (g m−2) LER LERN Partial LER Partial LERN

Oat + pea Oat + pea Oat + pea Grain Grain

Grain Grain N Grain Residue Grain Residue Oat Pea Oat Pea

Sowing ratio (%) (oat:pea)100:0 508b 11.0c

75:25 466bc 10.8c 0.93a 1.09a 0.97a 1.18a 0.89a 0.05c 0.92a 0.05c

50:50 454bc 11.2bc 0.91a 1.07a 0.96a 1.27a 0.77a 0.13b 0.82a 0.14b

25:75 443c 12.4b 0.85a 1.06a 0.88a 1.26a 0.53b 0.32a 0.56b 0.32a

0:100 557a 20.5a

Fertilization (g N m−2)0 449b 11.8b 0.98a 1.12a 1.06a 1.22a 0.77a 0.21a 0.84a 0.22a

6 508a 13.5a 0.92a 1.02a 0.95a 1.15a 0.77a 0.15b 0.80a 0.16b

12 499a 14.3a 0.79b 1.08a 0.80b 1.33a 0.65a 0.14b 0.66b 0.14b

Year2010 484a 13.1a 0.85b 1.10a 0.90a 1.39a 0.72a 0.13b 0.77a 0.13b

0.9

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2011 488a 13.3a 0.94a 1.05a

ifferent letters indicate significant differences (p < 0.05).

ocation, fertilization and Rhizobium inoculation (Igbasan et al.,996). In intercrops, Neumann et al. (2007) observed an increasef grain N concentrations in intercropped pea as competitionnhanced N allocation within the plant towards the seed whereaschmidtke et al. (2004) found that high competition of barleyowards intercropped lentils reduced allocation of assimilates tohe seeds and thus the grain N concentrations. In contrast, ouresults show that strong competition by oat did not alter pea grain N

oncentrations. In accordance with our results, Naudin et al. (2010)nd Wang et al. (2013) reported no differences in grain N concen-ration of pea between cropping systems.

ig. 3. (a–e) Nitrogen use efficiency (NUE), (f–j) partial factor nitrogen use efficiency (PFNertilization (main effect) and sowing ratio × year (interaction). Different letters indicate s***). SR = sowing ratio, Y = year.

8a 1.08b 0.74a 0.20a 0.76a 0.21a

The nitrogen harvest indices of both crops were reduced withN fertilization and with a decreasing share of the crops in themixtures. As reported earlier, the HI of pea decreased with Nfertilization whereas the HI of oat was unaffected, and in inter-crops the HI of both crops was reduced (cf. Neugschwandtner andKaul, 2014). Thus, the lower NHI of oat in intercrops showed thathigher grain N concentrations of oat could not make up for themore strongly reduced HI. Also Neumann et al. (2007) reported a

lower NHI for oat in intercrops but for pea a higher one with lessoat competition and an unchanged one with higher competition,concluding thereby that pea reacts to competition in intercrops

UE) and (k–o) nitrogen utilization efficiency (NUtE) of oat and pea depending on Nignificant differences, error bars are LSD (p < 0.05). Effects are significant at p < 0.001

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ith changes of the allocation of N within the plant towardseeds.

LERN had higher values than LER highlighting the influence ofigher grain N concentrations of oat in intercrops on overall pro-uctivity of the mixtures. Partial LERN showed that especially oatontributed to the N yields of the mixtures. Higher biomass and pro-ein yields in intercrops but a lower LER with high N fertilizationas already been reported for barley–pea intercrops by Chen et al.2004) and a lower LERN with fertilization in wheat–pea intercropsy Bedoussac and Justes (2011). Higher LERN of grain and especiallyesidue in the unfertilized treatment supports the observation byustec et al. (2010) that using legumes in intercrops is a sustainableay of introducing N into low input agro systems. Intercropping is

herefore especially of interest for low N input systems and organicarming systems (Bedoussac and Justes, 2010) where external Nnput is limited. As better economics with intercrops compared toheir pure stands have been reported (Lithourgidis et al., 2011;elzer et al., 2012) we assume that there will be an increasingcceptance of intercropping in European farming systems.

For total grain yields (oat + pea), the NUE and PFNUE were high-st for the pure stands of the crops, NUtE was highest for oat puretands and decreased with declining oat shares. The NUE can beanaged by seeding rate; for winter wheat pure stands, a decrease

f NUE with lower seeding rates has been attributed to a lower rootength density and a lower uptake of N from soil and from fertil-zer (Dai et al., 2013). Thus, with lower seeding rates, both cropsould neither alone nor together exploit the available N. The lowerUtE of oat and pea with lower intercrop shares is attributed to the

ower harvest indices and lower nitrogen harvest indices (cf. Dait al., 2013). A lower NUtE may be further caused by interferenceuring grain formation as observed in triticale-faba bean intercropsy Sobkowicz and Sniady (2004) especially for the suppressed crops the subordinate crop in mixtures is often vegetatively limited byhe taller crop (Gao et al., 2014).

. Conclusion

A clear understanding of yield formation, nitrogen yield anditrogen use and utilization in crop mixtures is a key compo-ent in developing intercropping systems. In oat–pea mixtures,igher grain yields than in pure stands could not be achieved. Con-equently, NUE and PFNUE for total grain yields were lower inntercrops and NUtE lower in intercrops than in oat pure stands.ut oat–pea intercrops could attain higher grain N yields than puretands without N fertilization. Thus, oat–pea intercrops are mostuitable for low input systems; growing oat–pea intercrops canlso be reasonable for producing grain feed as higher grain pro-ein yields are attainable despite lower total grain yields even on aertile soil.

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