The flux of N through mineralization–immobilization turnover (MIT) in grassland soils is a major determinant for plant N uptake and for N loss processes. In this study we investigated the dynamics of gross N transformation rates and potential N retention on mineral fertilizer addition in three permanent grassland soils of varying texture (loamy sand, loam, and clay loam). Gross N transformation rates were calculated with the 15N‐tracing model FLUAZ. Differentially 15N‐labeled NH4NO3 (at a rate of 100 mg N kg−1 soil) was added to the soils in paired laboratory incubation experiments. Size and 15N enrichment of the NH4+, NO3−, and soil organic N pools were measured at 0, 1, 3, 7, 14, and 30 d after NH4NO3 addition. The accuracy of the simulations of the data using FLUAZ were robust, but tended to decrease (i) with increasing incubation times, (ii) with increasing duration of the time intervals considered, and (iii) with increasing experimental variability. The proportion of the initial N content mineralized on incubation was largest in the loamy sand soil (2.5%), followed by the clay loam soil (1.2%) and the loam soil (0.8%). The actual gross nitrification and N immobilization activity followed the same trend. The loam soil showed the lowest relative N retention (ratio N immobilization over [gross N mineralization + gross nitrification]), which was attributed to its low C availability. In general, the 15N retention after addition of 15NH414NO3 was approximately five times larger than after addition of 14NH415NO3

BACKGROUNDThe mechanisms of calcium (Ca) absorption and transport in plants are still poorly understood. This study focused on assessing the absorption and distribution of Ca in different plant organs after root (soil), foliar, or fruit application to 6‐year‐old ‘Clemenules’ mandarin trees, grown in pots, using 45Ca as a tracer.RESULTSThe rate of 45Ca absorption and transportation in plant tissues varied according to the treatment method. The fruit and shoot Ca supply led to a rate of 97% to 98% 45Ca retention in such organs. In Ca‐treated fruits, 22% of the applied 45Ca moved to the pulp and 78% remained in the flavedo and albedo. The fruit peel was examined by scanning electron microscopy and transmission electron microscopy (SEM and TEM) and variations were observed during fruit development. Following 45Ca soil treatment, approximately 56% of 45Ca activity was measured in the soil, with 19.5% determined in the roots, 14.6% in the trunks (90% in bark and sapwood and only 10% in heartwood), 9.6% in shoots, and 0.3% in fruits.CONCLUSIONCalcium mobility in ‘Clemenules’ mandarin trees is limited and depends on the mode of Ca fertilizer application. The distribution of Ca to and within the fruits may be limited during development because of structural and functional constraints. © 2020 Society of Chemical Industry

Calcium (Ca) is often supplied to crop species to prevent the occurrence of Ca-related disorders. Mechanisms of Ca absorption and transport are not fully understood and the effectiveness of root and/or foliar Ca fertilization may be variable. To characterize the rate of Ca absorption and transport, trials were developed with chili pepper and sweet cherry plants, using 45 CaCl 2 as a tracer. The Ca treatments supplied were: (1) No 45 Ca (control); (2) 45 Ca soil application; (3) 45 Ca supply to basal leaves, and (4) 45 Ca application to apical leaves. After two months, plants were harvested for biomass and Ca content determination. The recovery of 45 Ca in different plant parts was measured with a liquid scintillation counter and leaf traits were observed by scanning electronic microscopy. In general, the highest 45 Ca concentrations were recovered in treated organs, while root applications led to highest 45 Ca translocation rates, which varied between chili pepper and cherry plants. For chili pepper, 45 Ca applied to the soil was detected mainly in roots (44 %) followed by leaves (36.6 %) stems (17.4 %) and fruits (2 %). In sweet cherry trees, soil-applied 45 Ca was principally recovered in roots (45.3 %), shoots (28.5 %), leaves (14.3 %) and trunks (11.9 %). The results provide evidence of increased absorption of root-applied Ca, as well as different degrees of Ca mobility between species. Foliar application led to major Ca increases in treated leaves, with Ca transported to other plant organs after apical leaf Ca supply chiefly in cherry trees.

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The Apalta catchment is a wine-producing area of 1300 ha, lying south of Santiago, located in the Colchagua Valley, near Santa Cruz in the VI Region of Chile. The vineyards are planted on slopes of up to 22 degrees, the rows being aligned mainly down the slope. This cropping system and its management lead to a potential contamination of natural resources. To assess the risk of environmental contamination due to the application of pesticides in different pest control strategies, indicators at a field level were derived according to a step-by-step procedure. Using these indicators, runoff was found to be the main process of impact. The different pest control strategies in this catchment caused different potential risks, though these in general were low.