Can foliar manganese supplementation increase rice productivity? A perspective on the morpho-physiological and yield traits

Manganese (Mn) is a fundamental micronutrient for several metabolic processes involved in plant growth and yield. Moreover, Foliar application of Mn contributes to increases in crop productivity, such as that of rice plants. Therefore, we hypothesized that these gains in rice productivity could be associated with increases in the photosynthetic capacities during grain filling, resulting from the foliar Mn supplementation in the rice plants. To this end, we cultivated rice plants in 10 L pots with floodplain soil, naturally low in Mn, under ambient conditions of an experimental field. These rice plants were treated with foliar application of Mn (1.5 kg ha−1 of Mn-carbonate as Mn source) during the tillering period and, subsequently, evaluated for morpho-physiological and yield characteristics. Rice plants were strongly influenced by foliar Mn supplementation, mainly for growth, concentration of Mn in different plant organs, and yield traits. The foliar Mn treatment promoted greater growth and production for the crop; however, photosynthetic characteristics (e.g. net CO2 assimilation rate and chlorophyll index) at the grain-filling stage were not affected by the Mn treatment. Our results suggest that the increase in rice productivity under foliar supplementation of Mn is not associated with photosynthetic activity, but is indicated by other possible mechanisms such as greater efficiency in the transport and storage of photoassimilates during the grain filling phase.