Integration of humic acid with nitrogen wields an auxiliary impact on physiological traits, growth and yield of maize (Zea mays L.) varieties

Abstract

A field experiments was conducted to investigate the soil application of humic acid and nitrogen levels at Agricultural Research Station, Swabi, Pakistan during 2014. Experimental soil was deficient in organic matter (0.52%) and total nitrogen (0.029%). Effect of humic acid and nitrogen levels on plant height, leaves plant-1, leaf area plant-1, leaf area index, grain yield, total N uptake, net assimilation rate as well as nitrate reductase activity in leaves were determined using maize variety Jalal and Iqbal. Four levels of humic acid (0, 0.6, 1.2 and 1.8 kg ha-1) and two levels of nitrogen (0 and 120 kg ha-1) were applied in soil along with basal fertilization of phosphorus and potassium. Nitrogen concentrations and uptake were determined from the grain and stover. All the applied levels of humic acid significantly enhanced growth and yield attributes of both maize varieties in the presence of nitrogen. However, application of 1.2 and 1.8 kg ha-1 were only effective to increase growth and yield attributes in the absence of nitrogen. Soil application of nitrogen significantly increased growth and yield of both maize verities; however, it was significantly lower than all the soil applied HA levels with nitrogen. Maize variety Iqbal showed significantly higher NR activity in leaves, net assimilation rate, grain yield and harvest index than Jalal. Nitrogen concentration and uptake were significantly augmented with increasing level of humic acid in grain and stover. However, maximum total N uptake was recorded with the application of 1.8 kg ha-1 HA+N in maize variety Iqbal. Among different applied HA levels, maximum grain yield was obtained from the soil application of 1.8 kg HA ha-1 with nitrogen in both varieties. Therefore, 1.8 kg ha-1 HA along with 120 kg N ha-1 in maize variety Iqbal could be recommended for higher grain yield in calcareous N deficient soil conditions.