Biological N Fixation and N Transfer in an Intercropping System between Legumes and Organic Cherry Tomatoes in Succession to Green Corn

The aim of this study was to investigate the transfer of N from different legumes to cherry tomatoes in the intercropping system under residual straw of the previous green corn crop using the 15N natural abundance method. We also investigated the temporal variation in nitrogen transfer to a cherry tomato, the biological nitrogen fixation (BNF) of legumes, and the N concentration of green corn cultivated in the intercrop succession. The experimental design was a complete randomized block with eight treatments and five replications, described as follows: two controls consisting of a monocrop of cherry tomato with or without residual straw, cherry tomato and jack bean, sun hemp, dwarf velvet bean, mung bean, and white lupine or cowpea bean in intercropping system. The BNF was responsible for more than half of the N accumulated in the legumes. The N of legumes was transferred to cherry tomato in similar quantities, and the leaves and fruits of cherry tomato received more N transfer than shoots. It was shown that N transfer increases with the growth/development of cherry tomatoes. The intercropping system with legumes did not affect the 15N natural abundance of leaves and the aboveground biomass of green corn cultivated in succession.

A Research Road Map for Responsible Use of Agricultural Nitrogen

Nitrogen (N) is an essential but generally limiting nutrient for biological systems. Development of the Haber-Bosch industrial process for ammonia synthesis helped to relieve N limitation of agricultural production, fueling the Green Revolution and reducing hunger. However, the massive use of industrial N fertilizer has doubled the N moving through the global N cycle with dramatic environmental consequences that threaten planetary health. Thus, there is an urgent need to reduce losses of reactive N from agriculture, while ensuring sufficient N inputs for food security. Here we review current knowledge related to N use efficiency (NUE) in agriculture and identify research opportunities in the areas of agronomy, plant breeding, biological N fixation (BNF), soil N cycling, and modeling to achieve responsible, sustainable use of N in agriculture. Amongst these opportunities, improved agricultural practices that synchronize crop N demand with soil N availability are low-hanging fruit. Crop breeding that targets root and shoot physiological processes will likely increase N uptake and utilization of soil N, while breeding for BNF effectiveness in legumes will enhance overall system NUE. Likewise, engineering of novel N-fixing symbioses in non-legumes could reduce the need for chemical fertilizers in agroecosystems but is a much longer-term goal. The use of simulation modeling to conceptualize the complex, interwoven processes that affect agroecosystem NUE, along with multi-objective optimization, will also accelerate NUE gains.

Intercropping—A Low Input Agricultural Strategy for Food and Environmental Security

Intensive agriculture is based on the use of high-energy inputs and quality planting materials with assured irrigation, but it has failed to assure agricultural sustainability because of creation of ecological imbalance and degradation of natural resources. On the other hand, intercropping systems, also known as mixed cropping or polyculture, a traditional farming practice with diversified crop cultivation, uses comparatively low inputs and improves the quality of the agro-ecosystem. Intensification of crops can be done spatially and temporally by the adoption of the intercropping system targeting future need. Intercropping ensures multiple benefits like enhancement of yield, environmental security, production sustainability and greater ecosystem services. In intercropping, two or more crop species are grown concurrently as they coexist for a significant part of the crop cycle and interact among themselves and agro-ecosystems. Legumes as component crops in the intercropping system play versatile roles like biological N fixation and soil quality improvement, additional yield output including protein yield, and creation of functional diversity. But growing two or more crops together requires additional care and management for the creation of less competition among the crop species and efficient utilization of natural resources. Research evidence showed beneficial impacts of a properly managed intercropping system in terms of resource utilization and combined yield of crops grown with low-input use. The review highlights the principles and management of an intercropping system and its benefits and usefulness as a low-input agriculture for food and environmental security.

A “toy” model of biogeochemical dynamics on climate gradients

We used a simple “toy” model to aid in the evaluation of the controls of biogeochemical patterns along a climate gradient. The model includes simplified treatments of water balance (precipitation minus Potential Evapotranspiration), leaching, weathering of cation- and P-bearing minerals, N cycling and loss, biomass production, and biological N fixation. We use δ15N as a central integrator of biogeochemical processes, because δ15N integrates multiple pathways of N input, output, and transformation in ecosystems. The model simulated the location and magnitude of a peak in δ15N on a gradient on Kohala Volcano, Hawai‘i which peaked ~ + 14 ‰ in sites receiving ~ 3.5 cm/month average precipitation (− 1300 mm/year water balance); the model also captured a peak in total P in surface soil at intermediate levels of precipitation and water balance, and other biogeochemical features on the gradient. We then applied the model to understanding the patterns of and mechanisms underlying nutrient limitation to net primary production (NPP) and plant biomass on the gradient, testing for the existence and extent of N and P limitation by simulated additions of N and/or P in the model. Both a simulated symbiotic biological N fixer and a simulated non-fixer were limited by P supply across the gradient; the non-fixer was independently limited by N supply in wetter sites. By running the toy model with and without the influence of temperature, we demonstrated that water is the most important factor shaping biogeochemical patterns on this gradient.

Seed size influences the promoting activity of rhizobia on plant growth, nodulation and N fixation in lima bean

ABSTRACT: This study evaluated the activity of rhizobia isolates inoculated in large (18 mm) and small (11 mm) seeds on lima bean growth, nodulation and N fixation. Selected rhizobia isolates were compared with a reference strain CIAT899 and two controls without inoculation. Large seeds contributed for highest plant growth, nodulation and N fixation than small seeds. The isolates UFPI-59, UFPI-18 and UFPI-38 promoted the highest values of shoot and root dry weight, respectively. The isolates UFPI-32 promoted the highest values of nodule number, while UFPI-59 promoted the highest values of nodule dry weight. The isolates UFPI-38 and UFPI-59 promoted the highest accumulation of N. This study showed that seed size really influences lima bean growth, nodulation and BNF. Considering rhizobia isolates, UFPI-59, UFPI-38, and UFPI-18 contributed for plant growth, promoted better nodulation and effectiveness on biological N fixation.

Affect of Rhizotorphin on chlorophyll content and productivity of introduced soybean cultivars

Biotic nitrogen fi is a phenomenon mainly depended on mutualistic interrelation between host plant and root nodule bacteria. This interrelation affects photosynthesis and productivity of biological N-fixation and requires studies of biological particularities of grown legume cultivars and effectiveness of Bradyrhizobium strains used for seed inoculation. A field experiment was conducted on the territory of Nesvizhskaya Crop Testing Station (Minsk region, Republic of Belarus). Based on chlorophyll and nitrogen content in soybean leaves, number of nodules on roots of cultivars grown, and on quantity of nitrogen accumulated in plants, four soybean cultivars were assessed. The cultivar Pripyat (control) has poorly responded on inoculation, whereas cultivars Slavyankа an Sobrini responded well by increase of chlorophyll and nitrogen content in leaves and by larger number of root nodules. As a result, they produced unusually high seed yields. Therefore, these soybean cultivars may be recommended for wide use in regions of Belarus.

Accumulation and Distribution of Fertilizer Nitrogen and Nodule-Fixed Nitrogen in Soybeans with Dual Root Systems

The soybean (Glycine max L. Merr.) is a crop with a high demand for nitrogen (N). The root nodules that form in soybeans can fix atmospheric N effectively, yet the goal of achieving high yields cannot be met by relying solely on nodule-fixed N. Nonetheless, the application of N fertilizer may inhibit nodule formation and biological N fixation (BNF), but the underpinning mechanisms are still unclear. In this study, we grafted the roots of non-nodulated soybeans onto nodulated soybeans to generate plants with dual root system. The experiment included three treatments conducted under sand culture conditions with NO 3 − and NH 4 + as N sources. Treatment I: The non-nodulated roots on one side received 50 mg·L−1 15 NO 3 − or 15NH4+, and the nodulated roots on the other side were not treated. Treatment II: The non-nodulated roots received 50 mg·L−1 15 NO 3 − or 15 NH 4 + , and the nodulated roots received 50 mg·L−1 14 NO 3 − or 14 NH 4 + . Treatment III: Both non-nodulated and nodulated roots received 50 mg·L−1 15 NO 3 − or 15 NH 4 + . The results showed the following: (1) Up to 81.5%–87.1% of the N absorbed by the soybean roots and fixed by the root nodules was allocated to shoot growth, leaving 12.9%–18.5% for root and nodule growth. Soybeans preferentially used fertilizer N in the presence of a NO 3 − or NH 4 + supply. After the absorbed fertilizer N and nodule-fixed N was transported to the shoots, a portion of it was redistributed to the roots and nodules. The N required for root growth was primarily derived from the NO 3 − or NH 4 + assimilated by the roots and the N fixed by the nodules, with a small portion translocated from the shoots. The N required for nodule growth was primarily contributed by nodule-fixed N with a small portion translocated from the shoots, whereas the NO 3 − or NH 4 + that was assimilated by the roots was not directly supplied to the nodules. (2) Based on observations of the shoots and one side of the roots and nodules in the dual root system as an N translocation system, we proposed a method for calculating the N translocation from soybean shoots to roots and nodules during the R1–R5 stages based on the difference in the 15N abundance. Our calculations showed that when adding N at a concentration of 50 mg·L−1, the N translocated from the shoots during the R1–R5 stages accounts for 29.6%–52.3% of the N accumulation in nodulated roots (Rootn) and 9.4%–16.6% of the N accumulation in Nodulen of soybeans. Through the study of this experiment, the absorption, distribution and redistribution characteristics of fertilizer N and root nodule N fixation in soybean can be clarified, providing a theoretical reference for analyzing the mechanisms of the interaction between fertilizer N and nodule-fixed N.

Effect of Fertilization and Bacterial Inoculation on Nutrient Status in Coal Mine Soil under Alder (Alnus sibirica) Plantation

This study was conducted to assess the effect of fertilization and nitrogen fixing (N-fixing) bacterial inoculation on the available nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg), present in the coal mine soil, by growing N-fixing plant species, alder (Alnus sibirica). The study was conducted in a greenhouse of the Forest Science Department, Chungbuk National University, South Korea, during the period of May 2019 to July 2019. A completely randomized design (CRD) comprising of four treatments, including T0—non-fertilized non-inoculation (control), T1—fertilization, T2—bacterial inoculation and T3—fertilization along with bacterial inoculation with three replications were used in the study. The results of the study showed that available N (NH4+-N and NO3−-N) in the coal soil were increased by the applied treatments for alder, as compared to control. Apart from control, difference was also found for increasing ammonium (NH4+-N) between treatments T1 and T3 and for increasing nitrate (NO3−-N) between treatments T1 and T2 and treatments T2 and T3. Available P and K in the soil also increased when NPK fertilizer was applied solely, and together with inoculation to the plants but reduced at other treatments. Therefore, it can be concluded that fertilization and biological N fixation in alder plant can improve the fertility of coal mine soil, and hence, this plant species could be a good option for the reclamation of degraded coal mine soil.