Root to shoot and carbon to nitrogen ratios of maize and soybean crops in the US Midwest

Abstract

Root traits are important to crop functioning, yet there is little information about how root traits vary with shoot traits. Using a standardized protocol, we collected 160 soil cores (0−210 cm) across 10 locations, three years and multiple cropping systems (crops x management practices) in Iowa, USA. Maximum root biomass ranged from 1.2 to 2.8 Mg ha−1 in maize and 0.86 to 1.93 Mg ha−1 in soybean. The root:shoot (R:S) ratio ranged from 0.04 to 0.13 in maize and 0.09 to 0.26 in soybean. Maize produced 27 % more root biomass, 20 % longer roots, with 35 % higher carbon to nitrogen (C:N) ratio than soybean. In contrast, soybean had a 47 % greater R:S ratio than maize. The maize R:S ratio values were substantially lower than literature values, possibly due to differences in measurement methodologies, genotypes, and environment. In particular, we sampled at plant maturity rather than crop harvest to minimize the effect of senescence on measurements of shoots and roots. Maximum shoot biomass explained 70 % of the variation in root biomass, and the R:S ratio was positively correlated with the root C:N measured in both crops. Easily-measured environmental variables including temperature and precipitation were weakly associated with root traits. These results begin to fill an important knowledge gap that will enable better estimates of belowground net primary productivity and soil organic matter dynamics. Ultimately, the ability to explain variation in root mass production can be used to improve C and N budgets and modeling studies from crop to regional scales.

The Effects of Soil Depth on the Structure of Microbial Communities in Agricultural Soils in Iowa (United States)

“…Deep soil cores were collected in the plant row during the mid-grain filling period (a period when root mass is maximum) ( 91 ) using a 6.2-cm-diameter Giddings probe. One soil core was collected in each of three plots that were arranged in randomized block design.…”

Yield Responses of Maize (Zea maysL.) and Successive Potato (Solanum tuberosumL.) Crops to Maize Stover co-compostedwith Calliandra CalothyrsusMeisn Green Manure

“…Moreover, on 6 maize varieties concomitantly evaluated in China and in the USA, Yu et al [74] found R/S ratios values ranging from 0.047 to 0.088, with a mean value of 0.08, identical to the value found in our study. In another study conducted in the US Midwest, R/S ranged from 0.04 to 0.13 for maize (Zea mays L.) and 0.09 to 0.26 for soybean (Glycine max L.) [73].…”

“…The R/S parameter represents the relative plant biomass allocated to plant tissues that have supportive functions (roots) to the amount of those (shoots) that have growth functions [71,73]. Among cereals, maize is characterized by high R/S values [67].…”

“…As handy as they could be, allometric relationships between below ground (roots) and above ground (shoots) biomass are affected by some limitations. They rarely take into account the effects of environmental and management factors [73][74][75][76]. Fertilisation generally decreases root growth and R/S values, whereas nutrient deficiency increases root growth and subsequently R/S values [74].…”

“…Fertilisation generally decreases root growth and R/S values, whereas nutrient deficiency increases root growth and subsequently R/S values [74]. Plants under soil nutrient and water stresses increase allocation of photosynthetic resources to roots (high R/S ratios), while plants under light limiting conditions develop and allocate photosynthetic resources to shoot growth (low R/S ratios) [73]. Based on this analytical statement, we can consider that the maize (Zea mays L.) crop installed in an open field experiment was not subjected to nutrient or water limitations.…”