Higher Root Length Density Research Articles

Formation of aggregates by plant roots in homogenised soils

The influence of root growth and water regime on the formation of aggregates was studied in modified minirhizotrons under controlled conditions. Two soils, a black earth (67% clay) and a red-brown earth (19% clay) were ground and forced through a 0.5 mm sieve. Ryegrass, pea and wheat were grown for fifteen wetting and drying (wd) cycles for 5 months. Another set of minirhizotrons was not planted and served as a control. Measurements of aggregate size distribution (ASD), aggregate tensile strength (ATS), aggregate stability (AS), aggregate bulk density (ABD) and organic carbon (OC) were made on single aggregates of the 2–4 mm fraction. The results showed that aggregates of the black earth which has a high clay content and shrink/swell properties had more smaller aggregates with higher ATS, AS and ABD than those from the red-brown earth. It was also found that for both soils: (1) w/d cycles and higher root length density (RLD) increased the proportions of smaller aggregates and aggregate strength; (2) differences in the ability of the plant species to influence aggregation was evident and seemed to be related to the RLD. The RLD was in the order ryegrass > wheat > pea. Mechanisms likely to be involved in processes of aggregate formation and stabilization are discussed. They include cracking of soil due to tensile stresses generated during drying of a shrinking soil; changes in pore water pressure within the soil mass caused by water uptake by plant roots generating effective stresses; and biological processes associated with plant roots and root exudates.

Effect of high frequency surface and subsurface drip irrigation on root distribution of sweet corn

Characterization of root growth and distribution is fundamental in explaining crop responses to irrigation and in determining appropriate management of irrigation systems, particularly with drip systems since it is widely believed that drip irrigation may limit the extent of root development. An experiment was conducted to study root distribution of sweet corn grown under high frequency surface (S) and subsurface (SS) drip irrigation, fertilized daily through drip systems at three phosphorus levels of P0 (no injected P), P1 (P injected at 67 kg/ha) and P2 (P injected at 134 kg/ha). Root sampling at the end of the growing season indicated that: (1) Root extension continued at depths in excess of 2 m in both the surface and subsurface drip at all P levels. (2) The greatest differences between SS and S treatments were observed in the top 45 cm depth. Higher root length density was observed in the surface 30 cm in S plots while the sweet corn in the SS plots had greater root length density than S plots below 30 cm, and (3) the greater root length density in the SS irrigated sweet corn was not reflected in a similar increase in total above-ground dry matter.

Importance of the subsoil for the K nutrition of crops

A K/Rb isotope dilution method was used to determine the uptake of K from undisturbed subsoils. Rb was applied to the topsoil (0–30 cm) to trace the K taken up from the topsoil by crops. The K/Rb ratio in the crops increases when roots contact the Rb-free subsoil. This change in the K/Rb ratio enables the calculation of the uptake of K from the subsoil. Results of 34 field experiments on loess-parabrown soils in N. Germany showed that the subsoil (>30 cm) supplied, on average, 34% of the total K uptake by spring wheat (range 9–70%). The range between the experimental sites is considered in relation to the contents of K in the top and subsoils (as extracted by 0.025 N CaCl2 solution), the proportion of the total root length in the subsoils, and competition for K between roots in the top and subsoil. In subsoils with similar K contents, uptake from the subsoil decreased significantly from 65 to 21% of total K uptake, as K contents in the topsoils increased from 4 to 8 mg K/100 g. On sites with the same K contents in topsoils (9 mg K/100 g), the subsoil supplied 12 to 61% of total K uptake as the K contents of the subsoil increased from 2 to 27 mg K/100 g. The contribution of uptake of K from the subsoil increased with the development of the crop, from 8% at first node stage to 35% at ear emergence, as the proportion of total root length in the subsoil increased. High root length densities in the topsoil (9 cm/cm3) resulted in competition for K between roots and increased uptake of K from the subsoil.

Rooting Characteristics of Four Intermountain Meadow Community Types

Healthy meadow communities generally have excellent soil binding properties. However, belowground characteristics of these communities have seldom been evaluated. In 4 meadow community types (CTs) we measured root mass and root length density (RLD) at 10-cm intervals to 40 cm soil depth. The CTs occurred along a wet to dry soil moisture gradient. The ranking of CTs from wettest to driest was: Carex nebrascensis (CANE) > Juncus balticus (JUBA) > Carex douglasii (CADO) > Poa nevadensis (PONE). Total RLD and mass to 40 cm paralleled the order of soil wetness, i.e., there were more roots at the wetter sites. Values of total RLD and mass for the 4 CTs were: 95.6 cm cm-3 and 3,382 g m-2 respectively for CANE; 33.6 cm cm-3 and 2,545 g m-2 for JUBA; 25.7 cm cm-3 and 1,526 g m-2 for CADO; and 8.8 cm cm-3 and 555 g m-2 for PONE. Root mass and RLD declined with depth, a result consistent with other graminoid systems. The RLD values for CANE, JUBA, and CADO are exceptionally high compared to literature values from other graminoid plant communities. The high RLD of the wet CTs suggests that they have superior sitestabilizing characteristics.

Differences in Drought Resistance between Two Corn Hybrids. II. Component Analysis and Growth Rates1

AbstractRelatively little research has been conducted to evaluate differing responses to water stress among genotypes of the same species. The objective of this study was to identify differences in growth and development of plant parts resulting from water stress imposed on two corn (Zea mays L.) hybrids that had been observed to differ in their sensitivity to water stress. During 1983 and 1984, two corn hybrids (Pioneer Brands 3192 and 3165) were subjected to three water management treatments: optimal irrigation, rainfed, and stress during vegetative (1983) or early reproductive (1984) growth. Growth analysis revealed few differences between hybrids for leaf area index, and crop and seed growth rates when well‐watered or stressed during vegetative growth, except that hybrid 3192 showed more rapid early growth. When well‐watered, grain yield of hybrid 3192 was the same (1983) or higher (1984) than grain yield of hybrid 3165. However, the two hybrids differed in their ability to resist severe water stress. The greater grain yield of hybrid 3165 in the rainfed treatment was associated with relatively smaller reductions in crop growth rate, total biomass accumulation, seed number, effective filling period, and harvest index with stress when compared to hybrid 3192. The greater crop growth rate and final biomass and grain yield of hybrid 3165 during severe stress most likely resulted from the maintenance of higher leaf water and turgor potentials and lower leaf diffusive resistances that were apparently mediated by higher root length densities in deeper zones of the soil profile as described in a companion paper.