Effects of potassium sulphate fertilizer rates on some of qualitative and quantitative traits of forage corn (Zea mays L.) in different irrigation regimes

Drought stress reduces plant growth by affecting photosynthesis and interlinked physiological process's functioning. Maintaining adequate potassium (K) is critical to plant drought resistant and increased cell membrane stability, root growth and total dry mass of plants living under drought conditions and also improved water uptake and water conservation. The aim of this study was to evaluate the effect of deficit irrigation and potassium on yield of forage corn and moderating role of potassium in the face of deficit irrigation.
Materials and methodsThe present research was conducted at Varamin during summer of 2011. The experiment was carried out on split plot based on randomized complete block design with six replications. The experimental factors consisted of two irrigation regimes as a main plot (full irrigation and deficit irrigation after 70 and 130 mm evaporation from class A evaporation pan, respectively) and potassium sulphate fertilizer (K2SO4) rates with 52% K2O as a split plot (0, 50, 100 and 150 kg ha-1). The single cross 704 was used in the present study.
Deficit irrigation (irrigation after 130 mm evaporation from class A evaporation pan) reduced number of leaves, stem diameter, ear height from the ground, leaf area index and protein content, about 16, 41, 36, 33 and 5 percent by compare to full irrigation (irrigation after 70 mm evaporation from class A evaporation pan). Potassium sulphate fertilizer at the rate of 50 kg ha-1 increased the protein content by 9% compared to the non-use of potassium sulphate fertilizer. The highest value of leaf area index was obtained using 150 kg potassium sulphate ha-1, which showed an increase of 8%. At the rates of 0, 50, 100 and 150 kg potassium sulphate ha-1, deficit irrigation reduced 58, 33, 29 and 27 percent of fresh forage yield and 59, 42, 39 and 28 percent of dry forage yield, compared to full irrigation conditions. In both of full irrigation and deficit irrigation conditions, the fresh (17 and 98%, respectively) and dry forage (38 and 105%, respectively) yields were increased to raise the value of potassium sulphate fertilizer from 0 to 100 kg ha-1 and then significantly reduced the values of these traits. The maximum values of fresh and dry forage yields in full irrigation (78749 and 26933 kg ha–1) and deficit irrigation (55828 and 16522 kg ha–1) were gained by plants treated with 100 kg potassium sulphate fertilizer ha–1. In full irrigation condition, the differences between 0 and 100 kg potassium sulphate ha-1 for dry and fresh forage yield was 11449 and 27196 kg ha–1, respectively. Also, under deficit irrigation condition, the difference between 0 and 100 and 100 kg potassium sulphate ha-1 treatments was 7515 and 8386 kg ha–1 for fresh and dry forage yield, respectively.
There were observed steeper slope of increasing the fresh (6.24 and 3.67, respectively) and dry forage yields (5.61 and 14.84, respectively) by increasing the amount of potassium from zero to 100 kg ha–1 in terms of deficit irrigation stress in comparison to full irrigation. As well as a slower slope of reduction of fresh (-2.31 and -7.19, respectively) and dry forage yields (-9.99 and -10.15, respectively) by increasing the amount of potassium fertilizer from 100 to 150 kg ha–1 in deficit irrigation in comparison to full irrigation condition shows the moderating role of potassium fertilizers in the face of deficit irrigation in maize.