Effects of Humic Acid and Phosphorus Fertilizer on Root, Root Hair, Phosphorus Uptake and Phosphorus Influx in Sugarcane (Saccharum officinarum)

Sugarcane cultivation has been revived in Khuzestan province of Iran since the 1960s and due to good results, it gradually began to grow from north to south of this region. Currently, sugarcane is cultivated in more than 100,000 hectares of the provinceand almost 25% of the country needs for sugar arebeing produced in this region. Sugarcane fields of Khuzestan province are mainly rich in lime percentage and poor in organic matter and phosphorus. Soil pH in this region of the country also is about 8-8.5 and phosphorus uptake by plants and phosphorus fertilizer efficiency in these soils (alkaline and calcareous soils) are expected to be low. The optimum use of phosphorus fertilizer and proper phosphorus uptake is essential for the quantitative and qualitative function of sugarcane plants. Due to the very low mobility of phosphorus in the soil, its uptake by plants such as sugar cane is affected by number of soil and plant factors (especially plant root characteristics). Changes in these factors can lead to a reduction or increase of P uptake by the crop.

Because of the role of organic compounds in the improvement of mobility and phosphorus uptake, the use of organic material has been considered in many types of research. Organic compounds can play a direct and indirect role in plant factors and in phosphorous uptake improvement. In this regard, a greenhouse pot experiment was conducted in 2016-2017 at Farabi Agro Industry Co, 35 km south of Ahvaz, Iran (48º 36' E, 30º 59' N). This research carried out by using three levels of humic acid (immersion of settes in three concentrations of 0, 0.3 and 0.5% of humic acid) as well as three levels of phosphorus fertilizer (triple super phosphate) 0, 50 % and 100% of the recommended amount in the region (250 kg/ha) in two different harvesting periods (45 and 90 days after planting). The experiment set up as a factorial, based on complete randomized design with three replicates. In this experiment, the effects of different levels of phosphorous fertilizers and humic acid on aerial part (shoot height, shoot dry weight), underground part (root length, root dry weight and root hair length), and also root CEC of sugar cane plant in two harvest times were studied. Finally, uptake and influx of phosphorus in different treatments were investigated.

As the results show, although the range of the changes was different, the use of humic acid could improve almost all of these factors. Shoot height, shoot dry weight in humic acid treatments showed a significant increase in both harvests compared to non-used humic acid treatments and also in phosphorus fertilizer treatments as the fertilizer levels rose. These results show that humic acid can increase the uptake of phosphorus from the soil reservoir (treatments without phosphorus fertilizer) and source of soil and phosphorus fertilizer (phosphorus fertilizer treatments). The underground plant parts have also shown similar results. Root length and root dry weights have also been shown positive results in humic acid treatments. Therefore, an increase in phosphorus uptake in non-use phosphorous fertilizer treatments or phosphorous fertilizer treatments, along with humic acid, relative to non-humic acid treatments could be explained. The humic acid application seems to increase the uptake capacity of phosphorus from soil and fertilizer sources by increasing root length and root dry weight. In addition, the use of humic acid in alkaline soil can increase the solubility of phosphorus in water and therefore the phosphorus uptake by the roots of the plant could be increased. Based on the results, using humic acid due to improved phosphorus fertilizer use efficiency, phosphorous uptake by plant is expected to be increased and hence the fertilizer use would be reduced. Phosphorus influx results had not the same direction with uptake and application of phosphorus fertilizer. P influx results showed an inverse relationship with root length. In other words, phosphorus uptake was more dependent on the root growth.

This study showed that it is possible to use humic acid in the practical form during the cultivating of sugarcane setts, but it seems that further research is needed to examine other important points such as the use of humic acid during plant growth season and other its application forms, such as spraying or application in irrigation water.