The capture and utilization of P and K, two non-mobile soil resources, were examined by decomposing crop production/unit area into uptake/unit area (capture) and production/unit uptake (utilization efficiency). Resource capture and utilization efficiencies by intercrops were compared to those of sole crops by contrasting intercrop means against the weighted means of sole crops. Weightings were based on the proportion of each species in the intercrop. On average, intercrops took up 43% more P (4 to 83%) and 35% more K ( 10 to 87%) than the sole crops. Where nutrients were not limiting, P and K uptake increased as dry-matter yield increased, evidence that uptake was a function of crop growth rather than conversely. Even where soil P was deficient, uptake by a dominated crop was decided more by factors that determined the outcome of competition than by P availability. The combined root systems, likely to be larger and functional for a longer duration under intercrops than under either sole crop, were postulated to explain the greater capture of non-mobile nutrients like P and K. An enlarged root system provides an expanded root surface area to which non-mobile nutrients can diffuse. For mobile nutrients which move to root surfaces largely by mass flow, shading of the dominated canopy may explain the positive association observed between intecrop dry-matter accumulation and Ca capture. Shading reduces carbon assimilation and transpiration of the understory canopy and, therefore, would reduce mass flow of Ca as well.Competition for P and K by intercropped species, even when nutrient supplies were abundant, was affected by degree of growth concurrency, canopy domination and planting geometry. When a dominating species was harvested much earlier than the dominated species, the uptake rate of the longer-duration crop usually recovered from competition after the first crop was harvested. Exceptions occurred when development of the dominated crop was so badly impaired during concurrent growth that vegetative enlargement was inhibited after harvest of the early species. Uptake rates by pigeon pea and cassava, which are exceptionally long-maturing species that have relatively low daily P and K uptake requirements, appeared capable of fully recovering even on soils in which nutrient availabilities were marginal for other species.
Tag: nutrient uptake
Mass flow and diffusion of nutrients to a root with constant or zero-sink uptake. 1. Constant uptake.
This paper deals with transport of nutrients in soil by mass flow and diffusion towards plant roots. The root system is assumed to consist of uniformly distributed cylindrical vertical parallel roots, all taking up nutrients at the same constant rate. Each root thus can be thought to be surrounded by a separate soil cylinder. Steady-state conditions with respect to flow of water to the root are assumed. Two situations with respect to the steady-state water flow are distinguished: one where replenishment of the water taken up by the root takes place at the outer boundary of the soil cylinder, and one where replenishment takes place uniformly over the soil cylinder. Analytical solutions to the transport problem are derived. The constant uptake condition leads to concentration distributions converging eventually to a steady-rate solution, where the decrease in concentration is independent of time. With these, the period of unconstrained uptake Tu, i.e., the period during which transport in the soil allows the required uptake, is calculated. It is shown that transport by mass flow is more important the stronger the nutrients are adsorbed by the soil. The solutions for the two situations of steady-state water flow are shown to differ only slightly.
Mass flow and diffusion of nutrients to a root with constant or zero-sink uptake. 2. Zero-sink uptake.
This paper deals with a model for zero-sink uptake of nutrients by a plant root. Transport to the root is by diffusion and mass flow. A solution for the transport equation is derived where the initial distribution of the concentration around the root is that of steady-rate as was obtained in the first of this set of papers. Also, relatively simple approximations of the analytical solutions obtained are derived. It is shown that a good approximation to the uptake rate is proportional to the average concentration. With the help of these approximations, macroscopic uptake by a root system can be calculated.
Nutrient harvesting-the tree-root safety net
The hypothesis that deep rooting trees intercept nutrients which have leached below the crop rooting zone and compete for nutrients less strongly than trees rooting mainly within the crop root zone was tested in a mixed alley-cropping system on an Ultisol in North Lampung, Sumatra by measuring uptake of 15N placed at varying soildepths. Gliricidia sepillm, with its predominantly shallow root system, competed strongly for N with the crop and took up little 15N from lower soil depths. In contrast Peltophorum dasyrrachis roots exhibited a higher nutrient uptake activity at lower soildepth thus providing an active ‘safety-net’. Root activity as well as root length density has to be taken into account when assessing the efficiency of the safety-net.i’rellnlnary modelling results using WaNuLCAS suggested that Peltophonlln roots inthe 40-60 cm soil layer could reduce leaching by 5-10% over the course of a maize crop cycle in the rainy season.
Approaches to modeling root growth and the uptake of water and nutrients
This review presents information about root systems of crops and trees and describes approaches that have been used to model uptake of water and nutrients in crops that may have application to agroforestry systems. Only a few measurements of the distribution of tree roots in agroforestry systems have been published and these are predominantly in alley cropping systems with young trees. Therefore, a major limitation to developing water and nutrient uptake models for trees is the lack of adequate measurements and conceptual models for describing the distribution of roots spatially and temporally. Most process-based modelling approaches to water and nutrient uptake integrate the activities of a single root over the whole root system. Several difficulties can be foreseen with applying these approaches to roots of older trees including the presence of mycorrhizal associations so that the root surface is not the site of uptake, the uncertainty as to whether all tree roots are active in taking up water and nutrients, and the fact that, unlike annual crops, trees have substantial reserves of nutrients that can be mobilised to support growth so that the notion of a plant demand regulating uptake may prove difficult to define. The review concludes that a programme of experimental measurements is required together with modelling using approaches both in which roots are implicit, and in which process-based models with roots allow competitive ability to be assessed.
A static model of nutrient flow on mixed farms in the highlands of western Kenya to explore the possible impact of improved management
Currently there is much interest in the potential role of agroforestry in the mitigation of nutrientdepletion in sub-Saharan Africa. Using data from farm surveys and trials static models of nutrient flowfor existing farm systems and improved agroforestry systems were constructed. These included boundary plantings of trees, hedgerow intercropping for green manure or fodder, and a well-managed zero-grazing system with moderate fertiliser inputs. The objective was to explore the possible impacton nutrient budgets of improved management options. Major nitrogen (N) losses (70% of total farmloss) occurred in the field and hedgerow compartments, principally through leaching and denitrification, which exceeded 60 kg N/ha per annum in all systems. However, there was uncertainty in predicted net mineralisation and the potential amounts of soil-N losses, and the study indicatedsubstantial potential for N mineralisation in deep subsoils. In contrast, phosphorus (P) was efficiently conserved in the farm system, and moderate additions of inorganic P fertilisers could maintain soil-P stocks. Net soil nutrient balances ranged from –39 to –118 kg N/ha per annum and from –7 to +31 kgP/ha per annum in the different simulated systems. N inputs through biological N fixation and deep N capture were significant in agroforestry systems (up to 122 kg N/ha per annum), but when trees were used for production purposes these additional inputs were offset by increases in consumable N harvested (grain, wood and milk) which ranged from 35 to 195 kg N/ha. Improved manure management reduced soil-N deficits by 70 kg N/ha per annum in a zero-grazing system with a highmanure flux. Research priorities for the humid highland farming systems include the quantification and dynamic modelling of (1) N mineralisation and N dynamics throughout soil profiles, (2) spatial and temporal patterns of N uptake by trees in agroforestry systems, and (3) nutrient budgets inlong-term systems trials
Estimating nutrient concentrations and uptake in rice grain in sub-Saharan Africa using linear mixed-effects regression
Context or problem: Quantification of nutrient concentrations in rice grain is essential for evaluating nutrient uptake, use efficiency, and balance to develop fertilizer recommendation guidelines. Accurate estimation of nutrient concentrations without relying on plant laboratory analysis is needed in sub-Saharan Africa (SSA), where farmers do not generally have access to laboratories. Objective or research question: The objectives are to 1) examine if the concentrations of macro- (N, P, K, Ca, Mg, S) and micronutrients (Fe, Mn, B, Cu) in rice grain can be estimated using agro-ecological zones (AEZ), production systems, soil properties, and mineral fertilizer application (N, P, and K) rates as predictor variables, and 2) to identify if nutrient uptakes estimated by best-fitted models with above variables provide improved prediction of actual nutrient uptakes (predicted nutrient concentrations x grain yield) compared to average-based uptakes (average nutrient concentrations in SSA x grain yield). Methods: Cross-sectional data from 998 farmers’ fields across 20 countries across 4 AEZs (arid/semi-arid, humid, sub-humid, and highlands) in SSA and 3 different production systems: irrigated lowland, rainfed lowland, and rainfed upland were used to test hypotheses of nutrient concentration being estimable with a set of predictor variables among above-cited factors using linear mixed-effects regression models. Results: All 10 nutrients were reasonably predicted [Nakagawa’s R2 ranging from 0.27 (Ca) to 0.79 (B), and modeling efficiency ranging from 0.178 (Ca) to 0.584 (B)]. However, only the estimation of K and B concentrations was satisfactory with a modeling efficiency superior to 0.5. The country variable contributed more to the variation of concentrations of these nutrients than AEZ and production systems in our best predictive models. There were greater positive relationships (up to 0.18 of difference in correlation coefficient R) between actual nutrient uptakes and model estimation-based uptakes than those between actual nutrient uptakes and average-based uptakes. Nevertheless, only the estimation of B uptake had significant improvement among all nutrients investigated. Conclusions: Our findings suggest that with the exception of B associated with high model EF and an improved uptake over the average-based uptake, estimates of the macronutrient and micronutrient uptakes in rice grain can be obtained simply by using average concentrations of each nutrient at the regional scale for SSA. Implications: Further investigation of other factors such as the timing of fertilizer applications, rice variety, occurrence of drought periods, and atmospheric CO2 concentration is warranted for improved prediction accuracy of nutrient concentrations.
Yields and the nutritive value of early harvested common bean (Phaseolusvulgaris L.) crop residues for ruminants
The yields and nutritive value of haulm (stem and leaf) and pod wall (HPW) crop residues of common bean early-harvested atthe green pod fill stage were measured in nine genotypes grown in two dissimilar environments (Boricha and Mandura) inEthiopia. The concentrations of total N, neutral detergent fibre (NDF) and acid detergent fibre (ADF), and the in vitro DMdigestibility (IVDMD), in the HPW fractions (stem, leaf and pod wall) were measured. At Mandura the yields of seed and HPWaveraged 1.03 and 2.26 t/ha, respectively, and varied (p0.001) among genotypes (0.31-1.57 t/ha and 1.19-2.93 t/ha,respectively). However no such differences among genotypes (p0.05) were observed at Boricha. Stem, leaf and pod wallcomprised 52.4, 23.1 and 24.5% of HPW, respectively. The concentrations of N, NDF and ADF, and IVDMD in the HPW, andthe HPW fractions, generally varied (p0.05) among genotypes. The digestible DM (DDM) yields of HPW ranged amonggenotypes from 0.75-1.81 t/ ha at Mandura, and averaged 1.89 t/ha at Boricha. N yield ranged from 35.3-70.3 kg N/ha atBoricha and 18.3-43.4 kg N/ha at Mandura. Since yields of seed were positively correlated with yields of HPW DM, DDM andN, common bean genotypes can be selected concurrently for seed and HPW yields. Uses of high-yielding genotype can doublethe N and DDM yields without reducing seed yield. The N and IVDMD of HPW residue showed that early-harvested commonbean is a high nutritive value feedstuff for ruminants. © 2021 Fundacion CIPAV. All rights reserved.
Deciphering microplastic ecotoxicology: impacts on crops and soil ecosystem functions
Review on microplastic toxicity in agroecosystems is scarce. Thus, we develop a conceptual model (based on literature to date) that describes various microplastic effects using a size-scale. We also classify crops depending on their observed responses, and discuss several conceptual mechanisms of soil functions. The model shows that microplastic effects on crops can be positive, toxic, lethal and no-effect. Predominantly, microfibers in a wide range of sizes can positively affect crops. However, toxic effects of microplastics with/without other pollutants are more common at different sizes. Surprisingly, biodegradable plastic effects are lethal, calling into question their environmental friendliness. No-effect on crops is also possible but less observed. Unlike other crops (e.g., wheat, maize and bean), only onion seems resistant to microplastics. Crop uptake of micro/nanoplastic demands a clear benchmark to ensure food-safety. Furthermore, mixed effects are observed on soil functions. Alternation in soil enzymes and litter decomposition can affect nutrients and organic matter biogeochemistry. Hydrophobicity can be induced by increasing evaporation. Shifts in microbial community structure and activities are inevitable.
Biofilm forming rhizobacteria enhance growth and salt tolerance in sunflower plants by stimulating antioxidant enzymes activity
Salinity stress is one of the major environmental stresses that impose global socio-economic impacts, as well as hindering crop productivity. Halotolerant plant growth-promoting rhizobacteria (PGPR) having potential to cope with salinity stress can be employed to counter this issue in eco-friendly way. In the present investigation, halotolerant PGPR strains, AP6 and PB5, were isolated from saline soil and characterized for their biochemical, molecular and physiological traits. Sequencing of 16 S rRNA gene and comparative analysis confirmed the taxonomic affiliation of AP6 with Bacillus licheniformis and PB5 with Pseudomonas plecoglossicida. The study was carried out in pots with different levels of induced soil salinity viz. 0, 5, 10 and 15 dSm−1 to evaluate the potential of bacterial inoculants in counteracting salinity stress in sunflower at different plant growth stages (30, 45 and 60 days after sowing). Both the bacterial inoculants were capable of producing indole acetic acid and biofilm, solubilizing inorganic rock phosphate, and also expressed ACC deaminase activity. The PGPR inoculated plants showed significantly higher fresh and dry biomass, plant height, root length and yield plant−1. Ameliorative significance of applied bacterial inoculants was also evidenced by mitigating oxidative stress through upregulation of catalase (CAT), superoxide dismutase (SOD) and guaiacol peroxidase (GPX) antioxidant enzymes. Increase in photosynthetic pigments, gas exchange activities and nutrient uptake are crucial salt stress adaptations, which were enhanced with the inoculation of salt tolerant biofilm producing PGPR in sunflower plants. Although increase in salinity stress levels has gradually decreased the plant’s output compared to non-salinized plants, the plants inoculated with PGPR confronted salinity stress in much better way than uninoculated plants. Owing to the wide action spectrum of these bacterial inoculants, it was concluded that these biofilm PGPR could serve as effective bioinoculants and salinity stress alleviator for sunflower (oil seed crop) by increasing crop productivity in marginalized agricultural systems. © 2020 Elsevier Masson SAS