Demand-Driven Technologies for Sustainable Maize ... - IITA

183Table 1. Physio-chemical characteristics of the soils of the experimental siteat the beginning of each cropping season.Properties 2002 a block2003 bHigh- N Low- N blockpH (1:1 H 2O) 6.20 5.20 4.90Organic C (g kg -1 ) 4.39 3.70 3.40Total N (g kg -1 ) 0.52 0.31 0.27P (Bray 1) (mg kg -1 ) 31.40 27.20 17.60Effective CEC (mol ckg -1 ) 4.00 2.70 2.00Exchangeable K (cmol kg -1 ) 0.16 0.20 0.10Exchangeable acidity (cmol kg -1 ) 0.40 0.10 0.20Cu (mg kg -1 ) 0.40 0.50 0.40Zn (mg kg -1 ) 0.52 0.80 0.90Mn (mg kg -1 ) 9.40 12.20 10.30Fe (mg kg -1 ) 22.00 16.10 15.30aAt the beginning of 2002, all blocks were uniformly depleted. Therefore, compositesamples were taken to determine fertility levels.bIn 2003, high-N block refers to blocks supplied with 90 kg N ha -1 while low-N blockrefers to blocks supplied with no N fertilizer or 30 kg N ha -1 . All samples were collectedbefore fertilizer application in each year.the West African savanna, it would make selection for low-N tolerancemore effi cient because the selection environment for drought-toleranceis more uniform and easier to control than that for low-N tolerance.The objective of the study reported here was to determine the effect oflow soil-N conditions on the performance of diverse maize genotypesdeveloped for tolerance to either N defi ciency or drought stress.Materials and MethodsSite and experimental designThe study was conducted in 2002 and 2003 at the experimentalfarm of the Institute of Agricultural Research, Zaria, Nigeria (7 o 38 ‘E, 11 o 11 ‘ N, 686 m asl). The soil is a fi ne-loamy, isohyperthermicPlinthustalf; USDA taxonomy. The experimental fi eld was divided intothree blocks (high-N block: 90 kg N ha -1 , low-N blocks (N-defi cient):30 kg N ha -1 and 0 kg N ha -1 ) without randomization of N treatments.All experiments at low N levels (0 and 30 kg N ha -1 ) were conductedin fi elds that had been depleted of N for two cropping seasons byplanting maize at high densities without N fertilizer and by cutting andremoving the biomass after each crop season. The physio-chemicalcharacteristics of the soil of the experimental site at the beginning ofeach cropping season are summarized in Table 1.In each block (for each N level), the experiments were laid outin a randomized complete block design with three replications. Plotsconsisted of four rows, 5 m long with spacing of 0.75 m between rowsand 0.25 m between plants to give a plant population of 53,333 plants