Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched 15N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (two-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44–58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha–1 and Peltophorum an estimated 42 kg N ha–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments.
Tag: nitrogen cycle
Nitrogen uptake of maize (Zea mays. L) from isotope-labeled biomass of Paraserianthes falcataria grown under controlled conditions
Roots can be an important though poorly quantified source of nitrogen (N) in agroforestry systems. Nitrogen uptake of maize using P. falcataria below- and aboveground biomass separately, and their combination, as source of N, was assessed in a controlled experiment using 15N isotope labeling techniques. The 15N-direct and the 15N-indirect labeling techniques were compared for discrepancies in measuring N cycling from P. falcataria tree residues. N contribution to maize production was as follows; 40–57% from below ground biomass and 10–18% from above ground biomass (P < 0.05). Residue N use efficiency (%rNE) by maize was between 99 and 106% for belowground biomass, 4–4.5% for aboveground biomass. This implies that though nutrient release characteristics of aboveground biomass are commonly used as a basis for selection of agroforestry trees, those of belowground biomass would be of fundamental importance as well. Combining P. falcataria below and aboveground biomass did not result in significant (P < 0.05) effects on N recovered by maize, suggesting the absence of decomposition interactions between the two bio-chemically contrasting residues. There were no significant methodological differences reflected in measured N cycled by maize from leaves (Ndfr); 15% and 18% as estimated by 15N direct and indirect method, respectively. The two methods compared very well (P < 0.05) as tools of estimating N cycling from surface applied leaves. However, the ability of the direct method to measure N without disturbing either the tree or the soil, would make it a more attractive and valuable tool in N cycling studies in agroforestry systems.
Giant milkweed (Calotropis gigantea): A new plant resource to inhibit protozoa and decrease ammoniagenesis of rumen microbiota in vitro without impairing fermentation
This study screened six different species of forest plants and then further evaluated the most promising plant, giant milkweed (Calotropis gigantea), for the potential to improve nitrogen utilization efficiency (NUE) through inhibiting rumen protozoa in vitro. Ground leaves of giant milkweed at 1.6 and 3.2 mg/mL decreased the counts of Entodinium cells by 41.30% and 58.89%, respectively, and damaged their cell surface structure. Dasytricha, Isotricha, Epidinium, Ophryoscolex, and Diplodinium were not affected, while total bacterial and archaeal populations did not decrease. Ammonia nitrogen (NH3-N) concentration decreased by 50.64% and 33.33% at 1.6 g/mL and 3.2 mg/mL, respectively. Volatile fatty acid (VFA) production and methane production remained unaffected, but butyrate production increased. The giant milkweed leaves contained (per gram of dry matter) 3636 μg phenolics including 205.9 μg of 3-hydroxybenzoic acid, 2079 μg flavonoids including 1197.5 μg of quercetin and 91.4 μg of myricetin, and 490 μg alkaloids including 219.8 μg of anthraquinone glycosides. The effective inhibition of Entodinium was accompanied by a decrease in NH3-N concentration, and methane production did not increase except for the dose of 1.6 mg/mL. Giant milkweed may be used as a new feed additive or an alternative to chemicals or antibiotics for sustainable animal husbandry enhancing NUE in ruminants.