Urea (46% N) was used as the N fertilizer. One-third of the applied N were uniformly broadcasted and
plowed into the surface soil (0-10 cm) shortly before sowing of maize and cotton, one-third were applied
between the V6 (sixth leaf) and V7 (seventh leaf) stages by hand before irrigation, and the rest were
applied at tasseling stages (15 August 2006 and 20 August 2007). Phosphorus, potassium and zinc were
applied only before sowing. The maize was irrigated ten times. A water meter was used to ensure the
accurate control of the volume of water delivered to each treatment. According to conventional maize
practices used by local growers, maize was planted in 50 cm rows with 25 cm between adjacent plants in
the row. Seeds were sown on 20 April in 2006, 22 April in 2007. Crops were harvested on 25 September
in 2006, 19 September in 2007. The choice of crop, irrigation and N fertilization as well as selection of
type of action was at the discretion of local farmers to ensure that the field experiment would be as
practice-oriented as possible.