Abstract:

Maize growth and yield are sensitive to soil water. However, the effects are related to maize growth stages. Fertilizers supply may influence the effect of soil water in different growth stage on maize yield, but few report focus on it.
The pot experiment and field experiment were conducted in the southern Loess Plateau. The purpose was to investigate effects of water supply levels in different growth stages on maize yield under different fertilizer levels. The pot experiment concerned soil water content in seedling stage, internode elongation stage, tasselling stage, filling stage and fertilizer levels. Soil water content included five levels (45%, 60%, 75%, 90% and 105% of field capacity) while fertilizer included normal fertilizer level (NL: 0.4 g N·kg^-1 dry soil+ 0.2 g P₂O₅·kg^-1 dry soil) and low fertilizer level (LL: 0.2 g N·kg^-1 dry soil+ 0 g P₂O₅·kg^-1 dry soil). The field experiment concerned irrigation in seedling stage (X₁), internode elongation stage (X₂), tasselling stage (X₃), filling stage (X₄) and N fertilizer rates (X₅). Irrigation water included five levels (0, 25, 50, 75 and 100 mm), and N fertilizer application also included five levels (0, 112.5, 225, 337.5 and 450 N kg/ha).
Maize yield of LL was significantly less than that of NL whatever soil water content was. Maize yield of NL was increased continuously with the increase of soil water content in the range of 45%–105%. However, the yield of LL was increased with the increase of soil water content and reduced when soil water content was more than 90% in seedling stage, tasselling stage and filling stage. In internode elongation stage, the yield both of LL and NL were increased continuously with the increase of soil water content in the range of 45%–105%. In all the stages, maize yields under soil water content of 45% or 60% were lower, compared with that of 75% (control). The yield reduction of NL was less than that of LL. Yield of the treatment with soil water content 45% and 60% in tasselling stage was less than that in other stages whatever fertilizer was, and that in seedling stage was more than that in tasselling stage but less than that in other stages.
Maize biomass of LL was significantly less than that of NL despite of soil water content. In all stages, biomass of LL and NL were increased continuously with the increase of soil water content in the range of 45%–105%. For LL and NL, the biomass of the treatment with soil water content of 45% and 60% in tasselling stage was less than that in other stages, and that in internode elongation stage was more than that in tasselling stage but less than that in other stages. Biomass of LL and NL was greater under soil water content of 90% and 105% than that of control in all stages.
Two regression models were set up according to data of the field experiment, describing the relationship of maize yield (Ygrain) or biomass (Ybiomass) and irrigation water in seedling stage (X1), internode elongation stage (X₂), tasselling stage (X₃), filling stage (X₄) and N rate (X₅).
Y_grain =12473.4+278.6X₂+585.4 X₅－427.4X₄X₅;
Y_biomass = 24321.8 + 224.2X₂ + 315.2X₃ + 1346.3X₅－280.1X₁²－468.3X₂²－198.2X₃²－232.7X₄²－437.0X₁X₂－
238.6X₂X₃－601.9X₄X₅
The results indicated that soil drought in all stages of maize growth resulted in the reduction of maize yield. However, the yield reduction was decreased by sufficient fertilizer supply, especially under severe drought. Maize yield was quite sensitive to water in tasselling stage, whatever fertilizers were applied. So it was very important for maize to avoid water stress during growing period. Internode elongation stage was another key stage sensitive to soil water in dryland. The increase of soil water content in the stage had more significant effect on maize yield when fertilizer was shortage. Drought in seedling stage also caused significant decrease of maize grain yield, especially when fertilizer was not sufficient. Maize yield was increased with the increase of relatively soil water content in the range of 45% to 90%, but which was changed by fertilizer supply and different stages of maize growth. The increase of maize yield was contributed more by fertilizer than by water. The effect of water on maize yield was also limited when fertilizer was shortage. In the present situation, more fertilizer supply is the main way to increase crop yield in the Loess Plateau.

Key words: Optimization of water supply, Dryland, Maize, Fertilizer, Yield