Effect of pea and spring cereals intercropping on grain yield and crude protein content.

The advantage of intercropping is beneficial biological interactions between crops and their different use of growth resources. Our experiment aimed at investigating the effects of pea intercropping with cereals on the improvement of cereal supply with nitrogen and protein content in grain on a loamy soil in organic farming conditions. It was carried out during 2007-2009 at the Lithuanian Institute of Agriculture in Dotnuva. Pea (Pisum sativum L) and spring wheat (Triticum aestivum L), spring barley (Hordeum vulgare L) oats (Avena sativa L), and triticale (x Triticosecale Wittm) were sown as intercrops 50:50 or as a sole crop. The results obtained during the experimental years showed that the productivity and quality of spring cereal sole crops or intercrops depended on the species of cereals and varied between different year's cultivation conditions. Grain productivity in some cases was estimated to be higher in the intercrops, however it was not stable in three experimental years. The protein content and yield in the grain of cereals grown in intercrops was positively affected by pea intercrops.


Introduction
The inclusion of legumes in crop rotations and intercrops can provide increased protein-rich yields and a more sustainable source of nitrogen, while on the other hand it saves cost by reducing the requirement for mineral nitrogen application (Anil et al. 1998, Crews & Peoples 2004).In many countries, legume plants have recently been receiving increasing attention from researchers and growers (Hauggaard-Nielsen et al. 2009, Mariotti et al. 2009, Stoddard et al. 2009, Mikić et al. 2010).Pea (Pisum sativum L.) is the most common legume in crop rotations and quite productive in temperate conditions, as well as in Lithuania (Auskalnis 2001).
Being one of the most popular plants in the organic cropping system, pea provides high quality forage, rich in crude protein and mineral elements (Corre-Hellou & Crozat 2005, Lauk & Lauk 2008).However, it is not less important for its ability to accumulate atmospheric nitrogen, on which depends the state of the whole crop rotation and agroecosystem, and possible farming benefi t.Pea is productive as main crops, but its vines could also be useful as a nitrogen source (Tripolskaja et al. 2008).Various soils are suitable for pea cultivation, but the crop yields best on moderately heavy loam (Dovydaitis 1992).However, due to its biological characteristics, pea cultivation is not so simple.Although of more recent cultivars, pea grown as a sole crop has some disadvantages -it is prone to severe lodging, which aggravates its harvesting and weed control.As a result, pea productivity is more dependent on proper soil and crop management (Auškalnis & Dovydaitis 1998, Auškalnis & Dovydaitis 1999, Maikštėnienė & Satkus 2000, Auškalnis 2001).When grown in a mixture, e.g. with spring barley (Hordeum vulgare L.), the crop does not lodge and in the conventional cropping system produces a grain yield of nearly 5 t ha -1 (Auškalnis & Dovydaitis 2000).Intercropping of cereals and legumes is widely used in low-input agriculture because the mixture of nitrogen N-fi xing and non-N-fi xing crop species provides complementarities in the utilization of resources, reduces weed pressure and sustains plant health (Hauggaard-Nielsen et al. 2003, Jensen et al. 2006).Mixing species in cropping systems may lead to a range of benefi ts that are expressed on various space and time scales, from a short-term increase in crop yield and quality, to long-term agroecosystem sustainability, up to societal and ecological benefi ts (Malezieux et al. 2009).
Our experiment aimed at investigating the effects of pea intercropping with cereals on the improvement of cereal supply with nitrogen and protein content in grain on a loamy soil in organic farming conditions.

Materials and Methods
The fi eld experiment was carried out on a loamy Endocalcari-Epihypogleyic Cambisol during 2007-2009 at the Lithuanian Institute of Agriculture in Dotnuva (55 o 24'N, 23 o 50 E).The soil pH varied at about 7.5, humus content was 2.3%, available P 74-79 mg kg -1 and K 135-140 mg kg -1 .Wheat (Triticum aestivum L.), barley, oats (Avena sativa L.) and triticale (x Triticosecale Wittm.) were grown as sole crops and intercrops with fi eld pea.The experimental plots were laid out in a complete one-factor randomised block design in three replicates.The intercrop design was based on the proportional replacement principle, with mixed pea grain and spring cereals grain at the same depth in the same rows at relative frequencies of 50:50.Wheat seeds rates were calculated on the basis of 5.5, barley 4.7, oat 6.0, triticale 4.5 and pea 1.0 million seeds ha -1 for sole crop.The crops were cultivated according to organic management practices.
The crops were harvested at complete maturity stage.Grain yield components were determined from plant samples taken before harvest.Grain dry matter (DM) yield was determined after threshing.Nitrogen was determined by Kjeldahl, while crude protein content was calculated according to the amount of nitrogen, by multiplying with 6.25 for pea and 5.7 for spring cereals.The LER values were calculated as follows (Mead & Willey 1980): The experimental data were processed by analysis of variance (ANOVA) applying Least Signifi cant Difference (LSD) test using the computer software Selekcija (Tarakanovas & Raudonius 2003).
The precipitation sums and the temperature means during experimental period are shown in table 1.

Results and Discussion
The number of the productive stems was signifi cantly lower in the intercrops than in sole peas or cereals (Tab.2) in all three years of experiment and naturally fl uctuated between years.Number of pea grain in intercrops was also lower, therefore number of cereals grain per ear was higher in intercrops and number of wheat and triticale was signifi cantly higher.In previous research on pea productivity on light loam soil, it was noticed that a stand density of 80-90 plants m -2 was suffi cient to produce a rather high yield (Auškalnis & Dovydaitis 1998) The results obtained during the tree experimental years showed that the productivity of spring cereal sole crops or cereal and pea intercrops depended on the species of cereals and cultivation conditions (Tab.3).
The productivity of spring wheat and barley intercrops in the 2007 was signifi cantly higher compared with that of the other intercrops and cereal sole crops, except for spring wheat (Tab. 3).The fact that intercropping of legumes and cereals produced higher yields than sole cereal crops without nitrogen fertilization was noticed by several researchers (Jensen 1996, Lauk & Lauk 2005).The cultivation conditions were different in experimental years, therefore the results varied.In the year 2008, yields of cereal intercrops were lower than in the 2007, because the climatic conditions were droughty in the summer of 2008.Oat and pea intercrop grain yield was the highest and the productivity of barley intercrop was insignifi cantly lower compared with the other intercrops.In 2009, yields of cereal intercrops were lower than in the 2007, however higher than in 2008 productive than sole cereal crops, except pea and oat intercrop and the most productive was pea and triticale intercrop.Some researchers noted that the yield of the intercrops was more stable than that of sole crops (Corre-Hellon et al. 2006).
In our experiment, pea and barley intercrop in two years out of three produced higher yield compared with the sole barley crop, however we could not conclude that this intercrop yielded more stably.
Even in organic agriculture it is diffi cult to obtain comparative values for protein contents of different cereals.Analysis of data showed that crude protein concentration of the intercropped cereals was improved compared to sole cereal crops in all experimental years, but was estimated lower than in sole pea (Tab.3).Differences in protein content in different cereals were recorded.The highest positive infl uence was achieved for intercropped triticale grain.In all three experimental years, protein concentration was signifi cantly higher than that in sole triticale.The lowest infl uence was observed in intercropped oat and the protein concentration was insignifi cantly higher than that in sole oat.The yield of crude protein in the intercrops varied between experimental years.Although the protein yield depended greatly on grain yield of crops, the yield of crude protein was determined to be lower in crops in 2008 and 2009 than in 2007.However, the yield of crude protein was increased in pea and cereal intercrops compared with cereal sole crops.Jensen et al. (2006) indicated that intercropping proved especially valuable for the production of protein on land with weed problems and for enhancing the grain protein concentration in cereals to levels, which were only likely to be obtained with high levels of animal manure.
The effi ciency of resource use in intercropping relative to sole crop from interropping expose LER values (Fig. 1) based on grain yield.Total LERs above 1.00 were found in case of barley in 2007 and 2009, of wheat in 2009 and of triticale in 2009 intercrops, which shows the advantage of these mixtures over sole crops.Other cases in terms of total LER showed some disadvantage of intercrops.LERs calculations based on crude protein yield strengthen demonstrate that intercrops produce more per area than its sole cereal crops.

Conclusions
The productivity of spring cereal sole crops or pea and cereal intercrops depended on the species of cereals and varied depending on different year's cultivation conditions.Grain productivity in some cases was estimated to be higher in intercrops, however it could not be concluded that pea/cereals intercrops yielded stably in three experimental years.However, protein content in the grain of cereals grown in intercrops was positively affected by pea and cereal intercrops.Pea-cereal intercrops can increase land use productivity.
L c +L p .Y cereal IC and Y peaIC are the intercrop yields and Y cerealSC and Y peaSC are the sole crop yields of cereal and pea respectively.A LER value above one indicates a benefi t of intercropping.