Evaluation of a New Approach to the 15Nitrogen Isotope Dilution Technique, for Estimating, in the Field, Crop Nitrogen Uptake from Organic Residues

Crop residue return is a nutrient conservation practice that benefits crop production while also improving soil quality. One of the difficulties that scientists encountered was determining a reliable technique for measuring N release from these residues and tracking their fate in the plant-soil system. The disadvantage of the direct isotopic labeling method, which involves labeling crop residues with 15N, is that it is very expensive and frequently complex. The indirect technique, which uses the 15N tracer and unlabelled residues simultaneously and is based on the principle of isotopic dilution, is simpler and less expensive than the direct technique. However, it has limitations due to the temporary organization of an amount of nitrogen of the 15N tracer in the presence of organic residues, which causes a dilution of the isotopic labeling that is unrelated to the mineralisation of the applied residues. This results in an overestimation of the plant’s use of nitrogen residues. A modified approach to this technique was proposed to reduce errors associated with N pools substitution. It entails labeling the soil with 15N and allowing it to settle for several months before applying unlabeled residues. The mineral nitrogen native to the soil and the nitrogen organized by microorganisms have a similar enrichment in 15N as a result of this soil pre-labeling. A field experiment was carried out to put the new method for estimating crop N uptake from suflower residues to the test. The soil had already been labeled. with 15N by fertilizing sunflower crops with 15N-fertilizer (Helianthus annuus L. var. Viki). 14N plots with unlabeled fertilizer were also established. At harvest, 15N-labeled residues were added to unlabeled soils (direct technique), and unlabeled residues were added to 15N-labeled soils (indirect technique) (indirect technique). There were also no-residue control plots established. The wheat (Triticum aestivum L. var merchouch) – sunflower (Helianthus annuus L. var. Viki) cropping sequence was used in all plots. The goal of this study is to put the new approach to dilution to the test in the field and compare it to the direct technique. If the estimates of crop N uptake from organic res are correct, If the results of the two techniques are similar, it will strongly support the validity of the new approach tested. In the cropping sequence, the first and second crops derived 6,92% and 3,62% of crop residues estimated by the direct method, respectively, and 7,95% and 4.24 percent estimated by the indirect method. The results revealed no significant difference between the two techniques, implying that the new soil pre-labeling technique compares favorably to the direct technique. It also has the advantage of being less expensive and simpler to use for a wide variety of organic residues, including the most complex.

Author (s) Details

Nabila El Alami
Faculty of Sciences, University Moulay Ismail, Meknes, Morocco.

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