Effects of Soil Amendment With Wood Ash on Transpiration, Growth, and Metal Uptake in Two Contrasting Maize (Zea mays L.) Hybrids to Drought Tolerance

Abstract

Wood ash as a soil amendment has gained wide spread acceptance in the recent years as a sustainable alternative to chemical fertilizers, although information regarding the effects of its application on maize growth and yield in the context of climate change and increasing drought severity is lacking till date. In the present study, field and pot trials were carried out at the experimental farm of the University of Padova at Legnaro (NE Italy) in a silty-loam soil in order to investigate the effects of soil amendment with wood ash (0.1% w/w, incorporated into the 0.2-m top soil) on the bioavailability of mineral elements and their uptake by maize. Characteristics analyzed included plant growth, leaf transpiration dynamics, and productivity in two contrasting hybrids, P1921 (drought sensitive) and D24 (drought tolerant). Wood ash contained relevant amounts of Ca, K, Mg, P, and S, and hazardous levels of Zn (732 mg kg^-1), Pb (527 mg kg^-1), and Cu (129 mg kg^-1), although no significant changes in total soil element concentration, pH, and electrical conductivity were detected in open field. Ash application led to a general increasing trend of diethylene triamine penta-acetic acid (DTPA)-extractable of various elements, bringing to higher grain P in D24 hybrid, and Zn and Ni reductions in P1921 hybrid. Here, the results demonstrated that ash amendment enhanced shoot growth and the number of leaves, causing a reduction of harvest index, without affecting grain yield in both hybrids. The most relevant result was a retarded inhibition of leaf transpiration under artificial progressive water stress, particularly in the drought-tolerant D24 hybrid that could be sustained by root growth improvements in the field across the whole 0-1.5 m soil profile in D24, and in the amended top soil in P1921. It is concluded that woody ash can be profitably exploited in maize fertilization for enhancing shoot and root growth and drought tolerance, thanks to morphological and physiological improvements, although major benefits are expected to be achieved in drought tolerant hybrids. Attention should be payed when using ash derived by metal contaminated wood stocks to avoid any health risk in food uses.

Keywords: corn; drought tolerance; leaf transpiration; nutrient availability and uptake; phenolic acids; progressive water stress; root growth; wood ash.

Figure 1

Field trial: dynamics of soil plant analysis development (SPAD) values as an index of leaf chlorophyll content in two maize hybrids (D24 and P1921) grown in ash-amended soil (Ash, 0.1% w/w) vs. untreated controld (Unt; n = 3). Asterisks indicate statistically significant differences between treatments within the same observation date (Newman-Keuls test, p ≤ 0.05).

Figure 2

Field trial: cumulated root length, root length density (RLD) pattern, and root electrical capacitance in two maize hybrids (D24 and P1921) grown in ash-amended soil (Ash, 0.1% w/w) vs. untreated controls (Unt; n = 3). Asterisks indicate statistically significant differences between treatments (Newman-Keuls test, p ≤ 0.05).

Figure 3

Field trial, harvest time: straw DW (stem + leaves + cobs), grain DW, harvest index (HI), and starch content in kernels of two maize hybrids (D24 and P1921) grown under ash-amended soil (Ash, 0.1% w/w) vs. untreated controls (Unt; mean ± SE, n = 3). Different letters indicate statistically significant differences between treatments within the same hybrid (Newman-Keuls test, p ≤ 0.05).

Figure 4

Field trial: concentrations of free phenolic acids in maize grains, cob, and straw (stem + leaves) of two maize hybrids (D24 and P1921) grown in ash-amended soil (Ash, 0.1% w/w) vs. untreated controls (Unt; mean ± SE for total concentration). Different letters within hybrids indicate statistically significant differences between treatments for total concentration (Newman Keuls test, p ≤ 0.05).

Figure 5

Field trial: element concentrations in grains, cob, and stem + leaves of two contrasting maize hybrids (D24 and P1921) grown in ash-amended soil (Ash, 0.1% w/w) vs. untreated controls (Unt). Differences between treatments (Newman Keuls test, p ≤ 0.05) within the same hybrid have been indicated with different letters (only when significant). Lead (Pb) was below the detection limit (b.d.l. < 0.003 mg kg⁻¹ DW).

Figure 6

Pot trial: dynamics of relative transpiration (RT) over the fraction of transpirable soil water (FTSW) of maize hybrids (D24 and P1921) grown in ash-amended soil (Ash, 0.1% w/w) vs. untreated controls (Unt) under progressive water stress. Regressions with the Linear-Plateau model. Coefficient c (critical point) indicated by the dotted line.