Flavio H. Gutierrez Boem

The K/Na and Ca/Na ratios and rapeseed yield, under soil salinity or sodicity

Rapeseed (Brassica napus) is a crop relatively tolerant to salt and sodium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of soil salinity or sodicity.Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three salinity levels (2.3 dS m-1; 6.0 dS m-1 and 10.0 dS m-1) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 and 44). The soil was kept near field capacity.As soil salinity increased, the K/Na and Ca/Na ratios in the tissues decreased markedly but yields and aerial biomass production were not affected. As soil SAR value increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na selectivities decreased. Plants could not maintain their Ca concentration in soil with a high SAR. The grain yield and biomass production diminished significantly in the highest SAR treatment. Our results are consistent with those showing detrimental osmotic effects of salts in Brassica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and biomass production. These results show that the effects of sodicity are different from those of salinity.

Note on the effects of winter and spring waterlogging on growth, chemical composition and yield of rapeseed

Abstract In regions where climatic conditions are adequate for rapeseed production soils may suffer waterlogging of varying duration. A pot trial was conducted to determine the effects of waterlogging on the growth, nutrient absorption and yield of rapeseed. As the effect of anoxia is known to depend on temperature the study was carried with winter or spring floods of 3, 7 or 14 days duration compared with a control without flooding. Seed yield was affected by 3 or more days of waterlogging. Winter waterlogging decreased the number of seed per plant, due to fewer branches, siliques and seeds per silique. Spring waterlogging, by contrast, reduced individual seed weight and seed oil content. The uptake of N, P, K and Ca decreased significantly with flooding but that of Na increased with spring waterlogging. Yield decline was greater with winter than with spring flooding. Temperature during the flooded period was not the only factor determining the effects of waterlogging: the stage of development, when waterlogging occurred, is also an important factor.

Seed number and yield determination in sulfur deficient soybean crops

ABSTRACT In soybean, seed number and yield is largely determined by the environmental conditions between initial bloom and the beginning of seed filling. Four field experiments were conducted to determine the effects of two sources of sulfur (S) on crop growth during the critical period of seed number determination and yield. Ammonium sulfate and gypsum were applied at a rate of 15 kg S ha− 1. Seed yield was closely related to the number of seeds per m2 (R2 = 0.93), but seed number was not related to crop growth between bloom and the beginning of seed filling. There was no effect of fertilization on aboveground biomass accumulation until the seed filling period began. The results from this study suggest that a moderate S deficiency reduced seed yield by affecting crop growth during the seed filling period. This late effect of a moderate S deficiency could be a consequence of the known high sulfate mobility in soils and low S remobilization in plants.

The effect of root exudates on root architecture in Arabidopsis thaliana

Root architecture is of key importance for plant nutrition and performance. It is known that root architecture is determined by genetics and environmental conditions. The aim of the present study was to evaluate if root exudation within a given plant has a role in the development of root architecture. We conducted a series of experiments using Arabidopsis thaliana Ler and Col grown with and without activated charcoal (AC). The addition of AC lowered the concentration of secondary metabolites in the growth media by more than 90%. Our results consistently showed that the addition of AC significantly decreased the number of lateral roots (38% in Ler and 27% in Col), but this decrease was compensated by an increase in the root length per unit of lateral root (83% in Ler and 96% in Col). This compensation resulted in a non-significant effect of AC on the total length of lateral roots. The effects of AC on root architecture were partially or totally reverted by the differential supplementation of root exudates from other plants of the same ecotype. Our results indicate a direct role of secondary metabolites present in the root exudates in the development of root architecture.

Distribution and vertical stratification of carbon and nitrogen in soil under different managements in the pampean region of Argentina

One of the expected benefits of no-tillage systems is a higher rate of soil C sequestration. However, higher C retention in soil is not always apparent when no-tillage is applied, due e.g., to substantial differences in soil type and initial C content. The main purpose of this study was to evaluate the potential of no-tillage management to increase the stock of total organic C in soils of the Pampas region in Argentina. Forty crop fields under no-tillage and conventional tillage systems and seven undisturbed soils were sampled. Total organic C, total N, their fractions and stratification ratios and the C storage capacity of the soils under different managements were assessed in samples to a depth of 30 cm, in three layers (0-5, 5-15 and 15-30 cm). The differences between the C pools of the undisturbed and cultivated soils were significant (p no-tillage > conventional tillage). Based on the stratification ratio of the labile C pool (0-5/5-15 cm), the untilled were separated from conventionally tilled areas. Much of the variation in potentially mineralizable C was explained by this active C fraction (R2 = 0.61) and by total organic C (R2 = 0.67). No-till soils did not accumulate more organic C than conventionally tilled soils in the 0-30 cm layer, but there was substantial stratification of total and active C pools at no till sites. If the C stratification ratio is really an indicator of soil quality, then the C storage potential of no-tillage would be greater than in conventional tillage, at least in the surface layers. Particulate organic C and potentially mineralizable C may be useful to evaluate variations in topsoil organic matter.

Soil Phosphorus Extracted by Bray 1 and Mehlich 3 Soil Tests as Affected by the Soil/Solution Ratio in Mollisols

Different relationships between soil-test methods results have been reported in several agricultural regions. Differences in the same soil-test procedure (e.g., soil/solution ratio) exist between soil-testing laboratories from different agricultural regions. Our objectives were to (1) determine the effect of soil/solution ratio on the amount of phosphorus removed by Bray 1 and Mehlich 3 methods, (2) compare the amounts of phosphorus removed by Bray 1 and Mehlich 3 in Mollisols from the Pampean region, and (3) determine whether soil/solution ratio affects the relationship between Bray 1 and Mehlich 3. Soil phosphorus availability was determined with two extractants (Bray 1 and Mehlich 3), using two soil/solution ratios (1:10 and 1:8, wt/v) in 72 soils (noncalcareous, loess-derived Molisolls) from the Pampean region. The amount of phosphorus removed was 20–24% greater when using 1:10 than 1:8 (wt/v) soil/solution ratio. This effect was significantly greater in Bray 1 than in Mehlich 3 (p = 0.04). When compared using the same soil/solution ratio, Mehlich 3 removed 4 to 8% more phosphorus than Bray 1. The soil/solution ratio used in the comparison affected the relationship between both extractants. The difference between extractants was slightly greater with a soil/solution ratio of 1:8 than of 1:10 (p = 0.03). Our results showed that even when using the same method, changes in the procedure (like soil/solution ratio) may cause different soil-test results and also differences in the relationship between two extracting solutions. Therefore, reported relationships between two methods are only valid for the soils and region where the relationship was developed and should not be extrapolated to other regions, even with similar soils.

Post-anthesis N and P dynamics and its impact on grain yield and quality in mycorrhizal barley plants.

An essential goal for modern agriculture is the simultaneous improvement of productivity efficiency and nutrient use efficiency. One way to achieve this goal in crops is to enhance nitrogen (N) and phosphorus (P) acquisition through the mycorrhizal association. This study examined the effect of mycorrhization on post-anthesis N and P dynamics and its impact on grain yield and quality in barley. In addition, the efficiency of both N and P utilization and remobilization was evaluated. With those purposes, barley plants inoculated or not with Rhizophagus intraradices were grown in a soil poor in N and P under greenhouse conditions. Inoculation with R. intraradices in barley enhanced both N and P content in grain and vegetative tissue and reduced phloem amino acid export rate. On the other hand, both N and P vegetative tissue content and phloem amino acid and P export rates decreased during grain filling, whereas N and P grain content increased in both treatments according to the senescence process. However, whereas N grain concentration decreased during grain filling, P grain concentration did not vary, thus suggesting a differential regulation on grain filling. Inoculation with R. intraradices improved the yield and grain quality, thus demonstrating that inoculation with R. intraradices in barley is beneficial, but mycorrhization caused a diminution in nutrient utilization efficiency. As the phloem remobilization rate of amino acids and P did not decrease during grain filling in R. intraradices-inoculated plants compared to non-inoculated ones, these results suggest that nutrient utilization efficiency is most probably regulated by sink strength rather by a mycorrhizal effect.

Phloem transport of assimilates in relation to flowering time and senescence in barley grown with different availabilities of nitrogen and phosphorus

ABSTRACT Understanding the way in which N and P availability affects the transport of sugar and amino acids is crucial to improve grain quality and yield. Thus, in the present study, two greenhouse and field experiments were conducted with barley plants grown with different N and P availabilities to assess the dynamics of the phloem transport of assimilates in relation to the beginning of flowering and senescence. The phloem transport of assimilates decreased before the beginning of protein degradation in all treatments, but the onset of flowering and senescence varied according to the N and P availability, as evidenced by the concentrations of proteins, amino acids, and sugar and the gene expression of senescence-related proteases and all glutamine synthetase isoforms. In N-deficient plants, the phloem transport decreased before flowering, but only when P was not limiting; in N- and P-sufficient plants it decreased at flowering; and in P-deficient plants it decreased after flowering. Therefore, only N-deficient but P-sufficient plants have a post-anthesis period with high export rate of assimilates. This alteration of phenology in relation to phloem leads to important consequences in assimilate utilization, as shown by the higher yield and N content of the former compared to P-deficient plants.

Interlaboratory and Intralaboratory Testing of Soil Sulfate Analysis in Mollisols of the Pampas

Sulfur (S) deficiencies in grain and forage crops have been detected in many agricultural regions of the world, but soil tests are not commonly used as the basis for S fertilizer recommendation programs. Errors of measurements of soil sulfate were determined to assess whether the variation among and within soil-testing laboratories could be a factor that prevent the adoption of soil testing to assess soil sulfate availability. Subsamples of 10 selected soils (Mollisols) from the Pampas (Argentina) were sent in two batches to five soil-testing laboratories. Laboratories were unaware of the existence of subsamples and performed routine sulfate analysis as if these soils came from 60 different fields. Soil sulfate ranged from 3.3 to 20.6 mg kg−1. One laboratory reported sulfate values greater than the other ones, having a mean bias of 4.1 mg kg−1 S sulfate (SO4). The other four laboratories reported similar sulfate values when soils had low sulfate availability (less than 10 mg S kg−1), even when they used different extractants. Considering only these four laboratories, average interlaboratory coefficients of variations ranged from 6 to 24% for the 10 soils. Within-laboratory mean coefficients of variation (CVs) ranged from 12 to 22%. However, mean absolute errors of all laboratories were less than 1.2 mg kg−1 S-SO4. Two laboratories reported different sulfate values for the two batches of shipment (an average difference of 4.7 and 3.8 mg kg−1 of S-SO4). Laboratories using different extractants obtained similar results, suggesting that using the same extractant is not a prerequisite to standardize laboratory results in these soils. Differences between laboratories in our study were smaller than in other interlaboratory comparisons for soil sulfate. These differences could be easily detected and corrected if laboratories participate in an interlaboratory control system. The observed low mean absolute errors suggested that, in general, all laboratories achieve acceptable precision when evaluating within the same batch of determinations. Differences between batches of shipment (within laboratory error) stressed the importance of using reference material for internal quality control.