Soil physico-chemical properties,biomass production,and root density in a green manure farming system from tropical ecosystem,North-eastern Brazil

Purpose

Soil physico-chemical properties, biomass production, and root density are considered key factors indicating soil health in an agroecosystem. The soil physico-chemical changes and plant growth (e.g., shoot biomass production and root density) in a 6-year cultivation of plant species used as green manure in a sandy soil from Tropical ecosystem, North-eastern Brazil, were investigated between July and December 2019.

Material and methods

We characterized soil physical and chemical properties, shoot biomass production, and root density under ten plant species used as green manure: Brachiaria decumbens Stapf. cv. Basilisk, Canavalia ensiformis (L.) DC, Crotalaria juncea L., Crotalaria ochroleuca G. Don, Crotalaria spectabilis Roth, Lablab purpureus (L.) Sweet, Mucuna pruriens (L.) DC, Neonotonia wightii (Wight & Arn.) J.A. Lackey, Pennisetum glaucum L., and Stilozobium aterrimum Piper and Tracy.

Results and discussion

The highest values of soil pH, exchangeable cations, CEC, and soil available water capacity were found on the plots where Poaceae plants were cultivated, whereas for H⁺+Al³⁺, C.E.C., soil available water, and soil available water capacity were found on the plots where Fabaceae plants were cultivated. On the plots where C. ensiformis and N. wightii were cultivated, we found the highest shoot dry biomass and root density, respectively. The results highlight the importance to consider plant species from both Poaceae and Fabaceae family used as green manure as soil conditioner (by promoting soil fertility, nutrient cycling, and hydraulic properties into plant root zone), and thus creating a positive plant-soil feedback.

Conclusions

Our findings suggest that (1) a consecutive green manure practice without any input of fertilizers after 6 years changed positively both soil physical and chemical properties, and improve plant growth (e.g., shoot dry biomass and root density) in tropical savanna climate conditions; and (2) by altering soil fertility, both Poaceae and Fabaceae plants used as green manure may create a sustainable cycle into the soil profile thus promoting soil health.

     

Production of Pearl Millet Irrigated with Different Levels of Brackish Water and Organic Matter

ABSTRACT

The objective is to determine the growth, yield and chemical characteristics of pearl millet irrigated with different levels of brackish water and organic matter in two cultivation cycles. The experimental design was randomized blocks in a 4 × 4 factorial arrangement, composed of 4 levels of brackish irrigation (25, 50, 75 and 100% evapotranspiration), 4 levels of organic matter (0, 15, 30 and 45 t ha^?1) with 3 repetitions. Along two cultivation cycles, pearl millet crop was analyzed for: plant growth variables, fresh and dry mass production, water-use efficiency, and chemical composition. There was significant interaction between applied water levels and organic matter for lignin in the 2nd cut (P < .05). The number of leaves, number of dead leaves and fresh mass production were influenced by the isolated effect of brackish water levels in cut 1 (P < .05). In turn, fresh mass production, dry mass production, plant height, leaves length, panicle length, fresh mass production, crude protein and ether extract were influenced by the isolated effect of saline water levels in the 2nd cut (P < .05). Growth, biomass production and chemical composition variables in second cut are positively influenced by different brackish irrigation levels under low rainfall conditions.     

15N-Urea Efficiency in Maize as Influenced by Humic Substances and Urease Inhibitors Treatments

Urea treated with urease inhibitors (UI) in association with humic substances (HS) is expected to improve urea efficiency by reducing ammonia losses and also provide the benefits of HS such as improve nitrogen (N) recovery by plants. Ammonia volatilization (AV), ¹⁵N recovery efficiency in the soil (NRE) and ¹⁵N use efficiency (NUE) were evaluated in maize (Zea mays L.) in a greenhouse pot trial. Treatments consisted of ¹⁵N-urea treated with UI (0, 0.4% boron (B) +0.15% copper (Cu), 0.64% B, and NBPT (N-(n-butyl) thiophosphoric triamide)) and three levels of HS (0%, 0.6%, and 1.2%). A control treatment (without N) was also included. N treatments were applied at V4 (vegetative leaf stage 4) on soil surface. HS was not efficient on AV reduction, NBPT had the greatest reduction in AV, and B had higher efficiency on AV reduction than Cu. At V8 (vegetative leaf stage 8), NBPT had the greatest NUE followed by B. At VT (tassel fully emerged), NUE from urea treated with NBPT reduced when increased levels of HS, and NBPT had the greatest NRE. UI in association with HS treated-urea does not reduce AV and it does not improve NUE by maize in vegetative stages.     

Spatial variability of short-term effect of tillage on soil penetration resistance

The effect of tillage on soil properties varies within field due to spatial variability of soils. Mapping changes of soil penetration resistance (PR) would be useful to understand and assess tillage practices to alleviate soil compaction. The objectives were to model the short-term effect of tillage on PR and its spatial structure, and to delineate homogeneous zones based on soil response in a Typic Argiudoll previously managed under no-till. A grid sampling for PR and soil water content (SWC) were performed before and after chiselling. Spatial analysis was performed on the effect of tillage on PR data by 10 cm layers and homogeneous zones were delineated by k-means cluster analysis. The effect of tillage was ?0.33 MPa in 10–20 and 20–30 cm layer. No differences of PR were found at 0–10 cm. Short range (5–7 m) spatial structure on the horizontal plane was observed in all layers. Only 45% of the field showed a marked effect of tillage on PR. Mapping the effect of tillage on PR would be a useful approach for evaluating the global and local response of soil to tillage, as well as for delineating of areas within field for site-specific tillage practices.     

Fostering sustainable water use in almond (Prunus dulcis Mill.) orchards in a semiarid Mediterranean environment

This work examines the long-term effects of deficit-irrigation (DI) practices in almond crop (Prunus dulcis Mill.) in agronomical and physiological terms. The trial was conducted during four-year monitoring period (2014–2017), in an experimental orchard (SW Spain), subjected to three irrigation regimes; i) a full-irrigation treatment (F_I), which received 100% of crop evapotranspiration (ET_C); ii) a regulated-deficit irrigation (RDI₅₀), which received 50% of ET_C during the kernel-filling period; and iii) a low-frequency deficit irrigation (LFDI), that was subjected to continuous periods of irrigation-restriction defined in terms of threshold values of leaf-water potential (Ψ_leaf) during the kernel-filling period. During the water stress period, there were monitored Ψ_leaf, stomatal conductance (g_s) and canopy temperature (T_C). Significant improvements in terms of water-use efficiency were found, as no differences in terms of yield between F_I and LFDI were found, leading to the conclusion that significant water savings (between 27 and 40%) can be achieved without compromising the yield. Moreover, threshold values of Ψ_leaf and thermal indicators were defined which will allow establishing future irrigation scheduling without compromising almond yield, especially when DI strategies are being applied.     

Coupling hysteresis analysis with sediment and hydrological connectivity in three agricultural catchments in Navarre,Spain

Purpose

Rain storm events mobilise large proportions of fine sediments in catchment systems. Sediments from agricultural catchments are often adsorbed by nutrients, heavy metals and other (in)organic pollutants that may impact downstream environments. To mitigate erosion, sediment transport and associated pollutant transport, it is crucial to know the origin of the sediment that is found in the drainage system, and therefore, it is important to understand catchment sediment dynamics throughout the continuity of runoff events.

Materials and methods

To assess the impact of the state of a catchment on the transport of fine suspended sediment to catchment outlets, an algorithm has been developed which classifies rain storm events into simple (clockwise, counter-clockwise) and compound (figure-of-eight; complex) events. This algorithm is the first tool that uses all available discharge and suspended sediment data and analyses these data automatically. A total of 797 runoff events from three experimental watersheds in Navarre (Spain) were analysed with the help of long-term, high-resolution discharge and sediment data that was collected between 2000 and 2014.

Results and discussion

Morphological complexity and in-stream vegetation structures acted as disconnecting landscape features which caused storage of sediment along the transport cascade. The occurrence of sediment storage along transport paths was therefore responsible for clockwise hysteresis due to the availability of in-stream sediment which could cause the “first flush” affect. Conversely, the catchment with steeper channel gradients and a lower stream density showed much more counter-clockwise hysteresis due to better downstream and lateral surface hydrological connectivity. In this research, hydrological connectivity is defined as the actual and potential transfer paths in a catchment. The classification of event SSC-Q hysteresis provided a seasonal benchmark value to which catchment managers can compare runoff events in order to understand the origin and locations of suspended sediment in the catchment.

Conclusions

A new algorithm uses all available discharge and suspended sediment data to assess catchment sediment dynamics. From these analyses, the catchment connectivity can be assessed which is useful to develop catchment land management.

     

A rapid method for the determination of chlorine, phosphorus, and sulfur in flours of grains and legumes using wavelength dispersive x-ray flourescence spectrometry

A rapid method for the determination of chlorine, phosphorus, and sulfur in commercial flours of wheat, barley, maize, rice, field bean, and soybean by wavelength dispersive x-ray fluorescence spectrometry has been developed. The flours are strained through a 425 microns sieve, then pelletized and measured. The total analysis time for the quantitation of chlorine, phosphorus, and sulfur is less than 20 min per sample. Calibration is carried out using a standard additions method with mixed standards. The method is accurate and precise, and appears to be adequate for routine analyses.     

Reduction of decomposition rates of scots pine needle litter due to heavy-metal pollution

Decomposition of unpolluted Scots pine needle litter was studied in two heavy-metal-pollution gradients in Sweden; one near a brass mill and the other around a primary smelter. In the latter area locally collected polluted Scots pine needle litter was also incubated. Decomposition rates were strongly influenced by the metal pollution and a decrease in the rate of mass-loss occurred. In the brass-mill gradient this occurred until about 1 km from the pollution source which corresponded to about 500 µg Cu and 1 000 µg Zn g^?1 soil. Data are presented to indicate that lignin decomposition was more sensitive to pollution than decomposition of whole litter and affected further away from the pollution sources. At the smelter sites, the metal-polluted needle litter decomposed more slowly than the unpolluted needle litter, and this difference was enhanced close to the smelter. The results indicate that heavy metals accumulated in needles prior to shedding have a long-term impact on the subsequent decomposition of the litter. Both litter quality and soil factors thus contribute to the reduced litter decomposition rate in metal-polluted forests. A new non-linear model with decreasing decay rate was used in the statistical evaluation. The model can be used to characterize the effects of pollution on decomposition rate.     

Effects of sewage sludge amendment on humic acids and microbiological properties of a semiarid Mediterranean soil

The residual effects of adding 40 t ha^–1 sewage sludge (SL) to a degraded soil cropped with barley were investigated after 9 and 36 months in a field experiment under semiarid conditions. The principal soil properties were apparently still affected by SL amendment 9 months after application but the effects disappeared after 36 months. With respect to control soil humic acids (HAs), the SL-HA was characterized by higher contents of S- and N-containing groups, smaller contents of acidic groups, a prevalent aliphaticity, extended molecular heterogeneity, and smaller degrees of aromatic polycondensation and humification. Amendment with SL caused an increase in N, H, S and aliphaticity contents and a decrease in C/N ratios and O and acidic functional group contents in soil HAs isolated 9 months after SL application. These effects tended to decrease after 36 months, most probably because the slightly humified SL-HA was mineralised over time through extended microbial oxidation, while only the most recalcitrant components such as S-containing and aromatic structures were partially accumulated by incorporation into soil HA. Microbial biomass, basal respiration, metabolic quotient and enzymatic activities increased in soil 9 months after SL application, possibly because of increased soil microbial metabolism and enhanced mineralisation processes. After 36 months these properties returned to values similar to those of the unamended soil, presumably due to the loss of energy sources.