Assessment of Root System Dynamics of Species Grown in Mixtures under Field Conditions using Herbicide Injection and 15N Natural Abundance Methods: A Case Study with Pea, Barley and Mustard

Abstract

Two methods were developed and used to study the root system dynamics of two species grown together or separately under field conditions. The first method, based on herbicide injection at different soil depths, was used to determine the rooting depth penetration rate of each species in pea-barley and pea-mustard mixtures. The roots absorbed the herbicide when they reached the treated zone leading to visible symptoms on the leaves which could be readily monitored. The second method used differences in 15 N natural abundance and N concentration between legume and non-legume species to quantify the contribution of each species to root biomass of a pea-barley mixture. Each contribution was calculated using 15 N abundance and N concentration of root mixtures and of subsamples of roots of individual species within mixtures. Both methods can indeed be used to distinguish roots of species in mixtures and thus to study belowground competition between associated species. The use of these methods demonstrated species differences in root system dynamics between species but also significant effects of interactions between species in mixtures. The rooting depth penetration rate was mainly species specific whereas root biomass was dependant on plant growth, allocation of dry matter between shoot and root components and growth factors such as N fertilization. Root biomass of each species may vary therefore with the level of competition between species.

The efficiency of a durum wheat-winter pea intercrop to improve yield and wheat grain protein concentration depends on N availability during early growth

“…This confirms that the cereal had access to a greater proportion of soil inorganic N when intercropped as compared with the sole cropping situation, supported by the increase in the percentage of plant N derived from N 2 fixation (% Ndfa) of pea which agrees with several other studies (e.g. Corre-Hellou 2005;Hauggaard-Nielsen et al 2003;Corre-Hellou and Crozat 2005). Hence, due to the complementary use of N sources by intercrop components, N accumulated by the whole intercrop was only slightly affected by N fertilization.…”

“…The advantage of such systems can be explained by the fact that the two intercropped species do not compete for exactly the same resource niche and thereby tend to use resources in a complementary way (Snaydon and Satorre 1989;Hauggaard-Nielsen et al 2001a, b). Cereals in particular seem to be more competitive for soil inorganic N (Jensen 1996) compared to grain legumes such as peas, due to faster and deeper root growth and the higher N demand of the cereal (Fujita et al 1992;Corre-Hellou 2005;Hauggaard-Nielsen et al 2003;Corre-Hellou and Crozat 2005). Consequently, the grain legume increases its reliance on symbiotic N 2 fixation (Li et al 2008).…”

“…Thus, when intercropped, the cereal should have access to a greater proportion of soil inorganic N because of greater interspecific competitive ability explained by a faster and deeper root growth and higher N demand of the cereal (Corre-Hellou and Crozat 2005), whereas the intercropped legume should increase its symbiotic N 2 fixation to satisfy its N requirements (Crozat et al 1994;Voisin et al 2002) as compared with sole cropping conditions.…”

Intercropping green manure crops—effects on rooting patterns

“…Staining roots with Congo red may facilitate the distinction of roots between monocot and dicot species (Ward et al 1978), but the stain is highly toxic and cannot be used in situations having more than two monocots or dicots. Injecting tracers or herbicides at different soil depths and spaces (Corre-Hellou and Crozat 2005;Hawkes and Casper 2002;Veresoglou and Fitter 1984) is useful to evaluate whether root activities of respective species exist at certain locations in the soil, but the data can vary greatly because the root distribution is not necessarily symmetrical; roots may not hit the tracer or herbicide patch by chance. In contrast, the multicolor staining method (injection of a dye solution to the root through the xylem) developed by Murakami et al (2006) can distinguish roots among several intercropped species.…”

Enhancing yield and profitability of cassava in the savannah and forest zones of Democratic Republic of Congo through intercropping with groundnut

“…These constraints can be effectively curbed through application of rational management utilizing the most appropriate cultural practices. Several advantages are attributed to intercropping, among them: (i) reducing the pressure of weeds, diseases and pests (Trenbath, 1993), thus making the practice an alternative to chemical control often criticized by proponents of conservation of the natural environment (Hauggaard-Nielsen et al 2001), (ii) reducing soil erosion through better coverage and good root development (Anil et al 1998), (iii) improving resistance to lodging (Anil et al 1998), (iv) reducing the leaching risk of nitrate (Corre-Hellou, 2005) and (v) better stability of interannual yield (Lithourgidis et al 2006). Intercropping reduces the use of chemical inputs and improves the economical and environmental performance of production systems.…”