Field Crops Research 133 (2012) 150–159 Contents lists available at SciVerse ScienceDirect Field Crops Research jou rnal h om epage: www.elsevier.com/locate/fcr Contribution of legumes to wheat productivity in Mediterranean environments of central Chile S. Espinoza a,b , C. Ovalle a,∗ , E. Zagal b , I. Matus a , J. Tay a , M.B. Peoples c , A. del Pozo d a Instituto de Investigaciones Agropecuarias, Centro Regional de Investigación Quilamapu, Casilla 426, Chillán, Chile b Universidad de Concepción, Facultad de Agronomía, Casilla 537, Chillán, Chile c CSIRO Sustainable Agriculture National Research Flagship, CSIRO Plant Industry, G.P.O. Box 1600, Canberra, ACT 2601, Australia d Universidad de Talca, Facultad de Ciencias Agrarias, Casilla 747, Talca, Chile a r t i c l e i n f o Article history: Received 17 January 2012 Received in revised form 9 March 2012 Accepted 9 March 2012 Keywords: 15 N natural abundance Farming systems Crop rotation Sustainable agriculture a b s t r a c t The potential benefits of using a legumes have not been evaluated in the rainfed, cropping systems of central Chile where wheat (Triticum aestivum) is typically grown in rotation with oats (Avena sativa) using high rates of nitrogen (N) fertilizer. Two experiments were initiated to compare unfertilized legume- wheat cropping sequences to the current oat–wheat system without and with applications of N fertilizer (160 or 207 kg N ha -1 ). One experiment was located in the interior dryland of central Chile (average annual rainfall 650 mm), and the other in the Andean foothills (average annual rainfall 1200 mm). Treatments were established in different areas of the same two experimental sites in consecutive years (2008 and 2009) resulting in four separate trials evaluating legume effects on wheat yield (2009 or 2010). Estimates of N 2 fixation determined using the 15 N natural abundance technique indicated that around 21 kg shoot N was fixed for every tonne (t) of shoot dry matter accumulated by either narrow-leaf lupin (Lupinus angustifolius), field peas (Pisum sativum), yellow lupin (Lupinus luteus), or white lupin (Lupinus albus) grown for grain, and by vetch (Vicia atroporpurea) grown in association with oats for green manure. When the amounts of N 2 fixed were adjusted to account for N in the nodulated roots, narrow-leaf lupin was calculated to have returned the lowest average net inputs of fixed N to the system following grain harvest (26 kg N ha -1 ) and field pea the highest (192 kg N ha -1 ). By comparison vetch in the green manure treatments where all above-ground biomass were incorporated into the soil returned 67 kg fixed N ha -1 . Depending upon location and year, growing grain legumes increased the subsequent N uptake by wheat by up to 60 kg N ha -1 (average 35 kg N ha -1 ) and vetch + oats green manure up to 103 kg N ha -1 (average 50 kg N ha -1 ). Wheat yields after grain legumes ranged from 2.4 to 3.0 t ha -1 in the interior dryland and 5.4–6.4 t ha -1 in the Andean foothills which were respectively 72–110% (90% average) and 69–83% (75% average) of the yields achieved by N fertilized wheat. Wheat yields after the vetch + oats green manure were 1.8 and 7.9 t ha -1 representing 60% and 102% of the yield of N fertilized wheat. In the absence of N fertilizer or legumes wheat yields after oats were around half that of the N fertilized wheat. It was concluded that grain legumes or legume-based green manures provide opportunities to greatly reduce the reliance of wheat production upon N fertilizer. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Many cropping systems traditionally utilized legumes to regen- erate the nitrogen (N) fertility of soils through the legume’s unique ability to fix atmospheric N 2 in a symbiotic relationship with the soil bacteria rhizobia. However, the practice declined drastically following the wide-spread availability of low-cost synthetic fertil- izers such as urea in the early 1960s (Crews and Peoples, 2004). In the dryland (rainfed) cropping areas of the Mediterranean cli- matic region of central Chile, bread wheat (Triticum aestivum) is ∗ Corresponding author. E-mail address: covalle@inia.cl (C. Ovalle). predominantly grown in rotation with oats (Avena sativa) and relies heavily upon N fertilizers applied at sowing and tillering to sup- port growth. Nitrogenous fertilizers represent >25% of wheat’s total production costs, and the dramatic increases in the price of fer- tilizers and other agricultural inputs that has occurred in recent years, combined with the recognition of the high energy costs and green-house gas emissions associated with the production, trans- port and use of N fertilizers (Crews and Peoples, 2004; Jensen et al., 2011) has stimulated the interest of both researchers and farmers to reconsider what role legumes may have in providing a reliable and renewable source of N for food production. The formation of root-nodules, the process of N 2 fixation within those nodules, and the legume’s subsequent reliance upon N 2 fix- ation for growth (proportion of N derived from atmospheric N 2 ; 0378-4290/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2012.03.006