Soil, cultivation practices and seeds sources
Two experiments were conducted in greenhouse conditions at the University of Missouri, Columbia, MO, USA,between July and October, 2009. Temperatures weremaintained at 26–30 : 22–26C
(day ⁄ night) with a 12-hphotoperiod of full sunlight (midday irradiance of 400–700 nm) and a photosynthetic photon flux density of1500 lmol m)2s)1at the top of the leaf canopy. Plantswere grown in 5-dm)3clay pots filled with sieved (5 mm)
air dry soil from the A horizon of a Mexico silt loam soil(fine, smectitic, mesic Aeric Vertic Epiaqualfs).
Soil in allpots was maintained at water content of 80% water-hold-ing capacity (0Æ33 g ⁄ g) with N-free water throughout the experiment. The soil physicochemical properties were(Corg:25Æ2gkg)1;P:15Æ87; K: 45Æ86; Ca: 1782Æ64; Mg:123Æ89; Fe: 80Æ70; Mn: 43Æ23; B: 14Æ06; Cu: 1Æ78; Zn: 9Æ82;Mo: 1Æ61 mg kg)1;pHCaCl2:6Æ77).