Variation in Nitrogen Rate and Local Availability Alter Root Architecture Attributes at the Onset of Storage Root Initiation in ‘Beauregard’ Sweetpotato

Abstract

<jats:p>This study characterized the influence of nitrogen (N) rates and variation in local availability on root architecture as measured by lateral root (LR) development attributes during the onset of the storage root (SR) initiation stage in ‘Beauregard’ sweetpotato adventitious roots (ARs). In N rate experiments, plants grown without fertilizer N showed significantly lower values for all measured LR attributes compared with fertilized plants. Total first- (1LR) and second-order LR (2LR) length increased by 78% and 2873%, respectively, as N was increased from 0 to 50 kg·ha<jats:sup>−1</jats:sup>. Total 1LR and 2LR number increased by 32% and 1465%, respectively. Increasing the N rates to 100 and 200 kg·ha<jats:sup>−1</jats:sup> did not result in further increases for all LR attributes measured. There were no differences in AR number between untreated controls and plants fertilized with 50 kg N/ha. However, the number of ARs increased by 65% when fertilizer N was increased from 50 to 100 kg·ha<jats:sup>−1</jats:sup>. Increasing the rate to 200 kg·ha<jats:sup>−1</jats:sup> did not result in further increases in AR number. In split-root experiments, roots grown in the compartment with 50 kg N/ha had 135% and 2916% increase in total 1LR and 2LR length, respectively, compared with roots grown in the compartment without fertilizer N. Total 1LR and 2LR number increased by 110% and 2114%, respectively. There were 111% more ARs in the fertilized compartment relative to the unfertilized compartment. There were no differences in LR attributes and AR number between compartments that received similar fertilizer N rates. In fertilizer placement experiments, there were no differences in LR attributes between pre-mixing fertilizer N and placement of fertilizer ≈4 cm below the surface of the growth substrate. There were also no differences between the unfertilized control and placement of fertilizer ≈4 cm from the bottom of the pot. Plants grown in substrate with pre-mixed N showed 38% and 342% increase in 1LR and 2LR length, respectively, relative to the bottom placement of N. Total number of 1LR and 2LR in the growth substrate with pre-mixed N increased by 30% and 312%, respectively, relative to the bottom placement of N. These results represent the first evidence for the association between sweetpotato root architectural attributes and variation in N rate and localized availability. These results are also consistent with findings in model systems in which local N presence is necessary for LR development. This information can be used to further optimize SR yield by helping to ensure the availability of N at the optimum rate across time and space.</jats:p>

Quantifying Storage Root Initiation, Growth, and Developmental Responses of Sweetpotato to Early Season Temperature

“…Therefore, any decline in storage root initiation, growth, and foliage growth could not be expected due to shortage of N in the plants. In other experiments where N or water deficits are variables, storage initiation and subsequent bulking were affected (Villagarcia et al, 1998; Gajanayake et al, 2013, Villordon et al, 2013).…”

Involvement of nitrogen in storage root growth and related gene expression in sweet potato (Ipomoea batatas)

“…Villordon et al . () found that lateral root branching of sweet potato was affected by N availability. Moreover, in sweet potato production, sandy soils are beneficial for improved formation and production of higher yields of storage roots; however, sandy soils also experience a high nitrate leaching risk (Yao et al ., ).…”

Hydrolyzed Organic Fish Fertilizer and Poultry Litter Influence Yield and Rhizosphere Ecology of Sweetpotato

“…For example, Jet and Mulkey (1996) reported that the applying N at 50.4 kg · ha -1 21 d after transplanting produced greater yields of US#1 storage roots compared with a higher rate. Villordan et al (2013) reported that lateral root length of storage roots increased substantially as N rates increased from 0 to 50 kg · ha -1 , whereas increasing the N rates to either 100 or 200 kg · ha -1 did not result in any further increases in root growth.…”