Enhancing Carbon Sequestration in Mediterranean Agroforestry Systems: A Review

ReviewThe agroforestry systems with a high potential for C sequestration are those degraded by poor management strategies. Studies on changes in soil C status in these ecosystems mostly take into account labile C pools. Labile and stable soil organic matter (SOM) fractions are affected by soil management and land-use changes. Stable C pools are essential to understanding effects of land-use on soil C storage in the long term. The SOM stability is partly enhanced by the interaction of SOM with minerals and its inclusion into soil aggregates. Recalcitrant substances (e.g., lignin and chitin) also contribute to the passive SOM fraction. Macroaggregates mostly reflect the influence of plant roots and coarse intra-aggregate particulate SOM (POM), whereas microaggregates reflect the influence of fine interaggregate POM, clay concentration and humified SOM fraction. Often, POM is more sensitive to soil management changes than total SOM. Glomalin is a recalcitrant protein consisting of chitin produced by mycorrhizal fungi to protect hyphae. Glomalin has implications on C sequestration in agroforestry soils, but further research is needed before any prediction can be made. One challenge is reducing the CO2 emission from roots, and increasing the recalcitrant root Cinfo:eu-repo/semantics/publishedVersio

Nitrogen distribution, remobilization and re-cycling in young orchard of non-bearing Rocha pear trees

In newly planted orchards, special attention must be paid to fertilization to build up the permanent structure of the trees so that high yield and fruit quality can be reached later on. Nitrogen (N) plays a major role in the fertilization plan, although few studies have assessed its use efficiency in young nonbearing trees, especially in field conditions. In this work, 1–3 years old ‘Rocha’ pear trees, grafted on quince BA29, were planted in a Mediterranean region, and fertigated with 6 g N tree 1 year 1 as ammonium nitrate with 5 at.% 15N enrichment to study the fertilizer N uptake during the vegetative cycle, the overall fertilizer N use efficiency at the end of each year, and the plant–soil N balance for this period. Nitrogen remobilization and the re-cycling of N from senescent leaves were also studied by fertilizing some pear trees with 10 at.% 15N enrichment. Nitrogen uptake was minimum at bud break and peaked in June/July remainingmore or less constant until leaf fall. About 25% of the fertilizer N taken up by 3 years old trees in the previous year was found in the new tissues formed (flowers, leaves and 1-year-old shoots), reaching 27% when fine roots were also included. In those trees, 32% and 54% of the 15N stored in the previous year in the trunk and older shoots, respectively, were mobilized to the new growth in the following year. Fertilizer N use efficiency by trees increased from the first to the third year but was generally small (6%, 14% and 33%), and estimated N losses were large (89%, 46% and 53%, respectively in the first, second and third years). Irrigation water and soil provided more N to the trees than fertilizer N

Underestimated role of legume roots for soil N fertility

Research ArticleNitrogen (N) is a major fertilizing element for plants. The distribution of N in legumes is influencing the efficiency of the next crop. Nitrogen storage in legumes is actually estimated by N fixation in shoots, whereas there is little knowledge on the contribution of roots and nodules to legume N and soil N. Here, we studied the contribution of roots and nodules of grain and pasture legumes to plant N and soil N in Mediterranean fields. Experiments were run under rainfed conditions for a 2-year period in three regions of Portugal. Entire plants including top plant and visible roots and nodules were sampled at the end of the growing seasons for grain legumes, sweet and yellow lupine, and over two harvests in case of pastures. N2 fixation was measured for grain legumes and pasture legumes using 15N tracing. Our results show that aboveground N concentration did not vary among legumes, but differed in the belowground tissues. Field studies show that 7–11%of total legume N was associated with roots and nodules. Data also show an allocation of 11– 14 kg N fixed t−1 belowground dry matter in indeterminate legumes, which represents half the amount of total aboveground plant. This finding demonstrates that investigation relying only on shoot Nunderestimates the role of legumes for soil N fertilityinfo:eu-repo/semantics/publishedVersio

Impact of application of urea modes and rates on yield and nitrous oxide emissions in grapevine (Vitis vinifera L.) on sandy soils in subtropical climate

Grapevines subjected to applications of nitrogen (N) doses on the soil surface can use only a small amount of the nutrient, probably because of losses, such as nitrous oxide (N2O) emissions to the atmosphere. An alternative to reduce these N losses may be the application of N via fertigation. The study aimed to evaluate the N2O emissions and grape yield (Vitis vinifera L.), in grapevines submitted to the application of modes and doses of N cultivated in sandy soil in a subtropical climate. 'Alicante Bouschet' grapevines were subjected to a factorial scheme with three N rates: 0, 40 and 80 kg N ha-1 year-1; and two application modes: surface (NS) and via fertigation (NF). Evaluations of N2O emissions and ammonium (NH4+) and nitrate (NO3-) contents in the soil, N concentration in leaves, grape yield, and number of clusters per plant were carried out. Grapevines cultivated with applications of 40 and 80 kg N ha-1 yr-1, in NF and NS modes, respectively, present-ed higher N2O emissions. N2O emission peaks occurred in the first 9 days after N application. Cumulative N2O emissions ranged from 161.74 ± 34.67 to 496.18 ± 37.00 g ha-1 of N2O-N, in soils that received 0 and 40 kg N ha-1 yr-1, respectively, both in NF mode. Accumulated N2O emissions had a linearly positive relation with the mineral N content in the soil (NH4+ and NO3-) and these had a negative relation with grape yield.  

Nitrogen Nutrition of Fruit Trees to Reconcile Productivity and Environmental Concerns

Although perennial fruit crops represent 1% of global agricultural land, they are of a great economic importance in world trade and in the economy of many regions. The perennial woody nature of fruit trees, their physiological stages of growth, the root distribution pattern, and the presence of herbaceous vegetation in alleys make orchard systems efficient in the use and recycling of nitrogen (N). The present paper intends to review the existing literature on N nutrition of young and mature deciduous and evergreen fruit trees with special emphasis to temperate and Mediterranean climates. There are two major sources of N contributing to vegetative tree growth and reproduction: root N uptake and internal N cycling. Optimisation of the use of external and internal N sources is important for a sustainable fruit production, as N use efficiency by young and mature fruit trees is generally lower than 55% and losses of fertilizer N may occur with the consequent economic and environmental concern. Organic alternatives to mineral N fertilizer like the application of manure, compost, mulching, and cover crops are scarcely used in perennial fruit trees, in spite of the fact that society’s expectations call for more sustainable production techniques and the demand for organic fruits is increasing

Avaliacao de alguns processos do ciclo do azoto em solos Portugueses, designadamente atraves do marcador 15N

It is necessary to obtain more detailed information on the processes involved in the N cycle of the soil-plant system. Thus, the fixing ability of several legumes was quantified and the N balance on Winter wheat, at Elves (Portugal) was evaluated, using "1"5#NU# isotope. Fababeans presented the highest fixing capacity (53 - 90% N derived from the fertilizer N dfa), even without inoculation, and under drought stress. Chickpea also showed a high fixing rate (44-80% N dfa), but total N_2 fixed was low (20 Kg N ha"-"1). Symbiosis with peas was depressed by water deficit and by Mo deficiency. Under favourable conditions, fixation rate reached 88%. Soybeans and green showed low fixation rates, probably due to inefficient rhizobium strains and/or inadequate plant genotypes. Sub clover mixed with non-legumes fixed 50% of its N in the above ground plant material, but no significant N transfer was observed to the non-legumes. The fertilizer use efficiency by Winter wheat was 19% - 44%. The fertilizer N recovered in the soil varied from 15% to 66%. Unaccounted N reached a maximum value of 55% of the applied N. Leaching of NO_3_- was the main loss, but denitrification and volatilization also occurredAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Yield Prediction Models for ‘Royal Gala’ and ‘Fuji Suprema’ Apple Varieties Cultivated under a Subtropical Climate

Nitrogen (N) effect on crop yield depends on several factors such as soil type, climatic characteristics and orchard management, including plant density and N fertilization. These variables can be used to develop yield prediction models, which are scarce in the horticulture sector. This study aimed to evaluate the effect of nitrogen fertilization, orchards and cultivars and to predict the yields of ‘Royal Gala’ and ‘Fuji Suprema’ apples cultivated in a subtropical climate under different soil N availabilities. During the four seasons, nitrogen fertilization was applied a rates of 0, 25, 50, 100 and 150 kg N ha−1 year−1 for ‘Royal Gala’ and ‘Fuji Suprema’ apples located in southern Brazil. Yield, average fruit weight and leaf and fruit pulp N concentration were evaluated. Yield prediction models were developed based on the following variables: concentration of N in leaves and fruits, air temperature, chilling units, relative humidity and rainfall. “Cultivar” was the variable responsible for the greatest variation of yield, followed by “years/season”, and then the “orchard management. The N rates applied in the four seasons did not predict crop yield. In the model, “orchard” was the greatest determinant for leaf N concentration, and “season” was the main determinant for fruit-pulp N concentration. Mathematical model (3), based on leaf and fruit pulp N concentration, and certain climatic variables (minimum air temperature, annual rainfall and chilling hours < 7.2 °C) had the greatest potential for predicting yield in orchards of ‘Royal Gala’ and ‘Fuji Suprema’

Nitrogen Transfer from Cover Crop Residues to Onion Grown under Minimum Tillage in Southern Brazil

<div><p>ABSTRACT Nitrogen derived from cover crop residues may contribute to the nutrition of onion grown under minimum tillage (MT) and cultivated in rotation. The aim of this study was to evaluate the N transferred from different cover crop residues to the onion crop cultivated under MT in southern Brazil. In June 2014, oilseed radish, black oat, and oilseed radish + black oat residues labeled with 15N were deposited on the soil surface before transplanting onions. During the growth season and at harvest, young expanded onion leaves, complete plants, and samples from different soil layers were collected and analyzed for recovery of 15N-labeled residue. Oilseed radish decomposed faster than other residues and 4 % of residue N was recovered in leaves and bulbs at harvest, but in general, N in plant organs was derived from sources other than the cover crop residues. In addition, leaf N was in the proper range for all treatments and was adequately mobilized to the bases for bulbing. The N derived from decomposing residues contributed little to onion development and the use of these plants should be chosen based on their advantages for physical and biological soil quality.</p></div