M. Silberbush

Sensitivity of simulated phosphorus uptake to parameters used by a mechanistic-mathematical model

SummaryChemical methods for determination of soil P available to plants do not take into account the effect of roots on P uptake by the plant. Moreover, the relative significance of root parameters, as compared to soil supply parameters in determining P uptake, is unknown. Simulation models have been verified for P uptake by corn (Zea mays L.) and soybeans (Glycine max L. Merr.). The objective of this paper was to use the Cushman simulation model, which has 11 plant and soil parameters, for a sensitivity analysis of the parameters involved in P uptake. Initial parameter values were those obtained from soybeans grown in Raub (Aquic Argiudoll) silt loam. Phosphorus uptake was simulated with each parameter changed independently, from 0.5 to 2.0 times initial value while all the other parameters remained constant. In addition, P uptake was simulated where interrelated parameters were changed according to their dependence. Root growth rate and root radius were the most sensitive parameters influencing P uptake. Soil P supply parameters were more sensitive than root physiological uptake parameters. Phosphorus concentration in soil solution affected P uptake more than the diffusion coefficient and buffer power. Reduction of root radius while root volume was maintained constant by increasing root length increased P uptake. Where both soil volume and root volume were kept constant, reduction of root radius to the size of root hairs or mycorrhizal hyphae gave the greatest P uptake.

Physiological aspects of ammonium and nitrate fertilization

Abstract Various physiological effects of ammonium, nitrate and mixed ammonium‐nitrate nutrition of plants have been studied in this laboratory during the last years. Some of the characteristic distinctions observed between plants growing on these nitrogen sources are described and discussed. Biomass production of ammonium‐grown plants increased with K+ concentration in the nutrient medium between 0.1 to 3 mM , while nitrate‐fed plants reached maximal growth around 0.25 mM K+ . The water use efficiency (WUE) of ammonium‐fed plants was lower and also more dependent on K+ than that of plants receiving nitrate. At low K+ levels (0.1 mM) in the medium, plants growing on ammonium‐N spent nearly twice as much water through transpiration per unit mass than nitrate‐fed plants. WUE of plants receiving NH4NO3 was poor at low K+ (similar to ammonium‐fed plants) but at high K+ this plants grew even better than nitrate‐grown plants. Overall transpiration per plant was little affected by K+ levels in the medium. Conseq...

Simulation study of nutrient uptake by plants from soilless cultures as affected by salinity buildup and transpiration

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis–Menten active mechanisms for K+, NO3−-N, NH4+-N, PO4-P, Ca2+, Mg2+ and SO42-, whose influx parameters are affected by Na and Cl−, but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations–anions concentrations is balanced by Cl− to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO3− and K+ uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K+ uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.

Salinity and nitrogen nutrition studies on peanut and cotton plants

Abstract The effect of the nitrogen form (NH4 + or NO3 ‐) added to the nutrient solution and salinity levels (NaCl) was studied in peanut and cotton plants grown in hydroponics. Salinity levels particularly affected the growth of NH4 +‐fed plants. Salinity and nitrogen form had different effects in the levels of K+ and Na+ in the shoots of these two species. Salinity only reduced photosynthesis in severely stressed cotton plants. A high correlation was observed between the level of K+ and stomatal conductance. Ammonium resulted in a less efficient use of nitrogen under saline conditions for both species.

Wheat growth as affected by nitrogen type, pH and salinity. I. biomass production and mineral composition

Abstract The interactions among the form of N supplied (ammonium or nitrate), NaCl concentration, and pH of the nutrient solution were studied on wheat (Triticum aestivum L. cv. Barkai) grown hydroponically. Plant growth was affected by increasing NaCl concentration from 0 to 100 mM. Increasing the pH from 5 to 8 resulted in reduced growth of ammonium‐fed plants, but not of nitrate‐fed plants, at all concentrations of NaCl applied. Potassium concentration in the shoot was inversely correlated with Na, but directly correlated with shoot dry weight. These correlations were affected, however, by the form of N in the nutrient media. The sensitivity of ammonium‐fed plants to NaCl may be due mainly to the decreased concentration of K in the shoot.

Physiological studies on salinity and nitrogen interaction in alfalfa. I. Biomass production and root development

Abstract The effects of the interaction between salinity, nitrogen (N) forms and concentration were studied with alfalfa (Medicago sativa L.) grown in pots with fine sand under greenhouse conditions. Increased salinity (0–100 mM NaCl) substantialy reduced the dry weight of roots and shoots, relative growth rate (RGR) of the plant, relative multiplication rate of root, mean extension rate of root, number of root branches, and root length. Additional N considerably moderated the salinity effects on these parameters. The promotive effect of nitrate‐N was more pronounced on shoot and root dry weight and root lengths while number of root tips relatively increased more by ammonium‐N on all salinity levels. Moreover, salinity affected root length per plant relatively more than number of root tips per plant. The plants were relatively tolerant at the second harvest to salinity and N levels. It is suggested that exogenous supply of N as nitrate would improve the vegetative growth of alfalfa by moderating the suppr...

RESPONSE OF MAIZE TO FOLIAR VS. SOIL APPLICATION OF NITROGEN–PHOSPHORUS–POTASSIUM FERTILIZERS

ABSTRACT Foliar fertilization is a widely used practice to correct nutritional deficiencies in plants caused by improper supply of nutrients to roots. The aim of the present study was to determine the efficiency of different forms of nitrogen–phosphorus–potassium (NPK) fertilizers applied to maize (Zea mays L.), either to the soil or to the leaves. Two sweet corn plants (CV Jubilee) were grown in plastic bags with 10.5 kg silt loam desert soil (Typic Haplocalcid). Before planting, the soil was mixed with zero (control), half or full dose of 0.6 g N, 0.4 g P, and 0.3 g K per pot as mineral forms, or as the “Global-Green” (GG) foliar fertilizer. Three forms of foliar fertilization were applied once a week in equivalent concentrations of N, P, and K (0.12 g N, 0.08 g P, and 0.06 g K/L): Mineral forms (NPK), GG, and “Fertilizers & Chemicals” (F&C) foliar fertilizers; plain water acted as the control. The plants were harvested after 55 days. The roots were washed from the soil and length measured. The shoots were measured for leaf area, fresh and dry wt, and leaf contents of chlorophyll, N, P, and K. All indices increased in response to all forms of foliar fertilization (FF), but no significant difference was obtained between the different forms. Global-Green was less effective as a soil fertilizer (SF) than NPK. The effectiveness of FF appeared to be limited by the holding capacity of leaf surface area for the liquid fertilizer. It was concluded that FF may partially compensate for insufficient uptake by the roots, but requires sufficient leaf area to become effective.

Use of an hydrophilic polymer to improve water storage and availability to crops grown in sand dunes I. Corn irrigated by trickling

Abstract The polyacrylamid (PAM) hydrophilic gel Agrosoak® was tested as a soil conditioner for improving water availability to crops grown on sand dunes. Corn ( Zea mays L.) was grown in the field, in a factorial design array using four rates of Agrosoak (0.00, 0.15, 0.30, 0.45% by weight in the upper 25 cm of the soil), three water amounts (70, 85 and 100% of the recommended Class A evaporation pan ratio), and two water salinity levels (1.2 and 6.5 dS·m −1 ). Irrigation and fertilization were provided by trickling. The water storage capacity of the soil increased with the rate of Agrosoak but the applied water was accumulated and stored in the vicinity of the emitters leaving relatively dry sections between the drippers. This caused a reduction in the density of the plants. Even so, yield components, except shoot dry weight per meter (cob yield per plant and per meter, and shoot dry weight per plant) increased with the Agrosoak application rate. Concentrations of nitrogen and sodium in the leaves increased, but phosphate and potassium were unaffected by the Agrosoak application rate with the use of fresh water or brackish water. The use of Agrosoak did not avoid salinity damage to the plants. The results show that the use of trickle irrigation with PAM soil conditioner require a reevaluation of the method of irrigation.

Calibration of minirhizotron readings against root length density data obtained from soil cores

The minirhiozotron (MR) root observation method was studied versus root length density (RLD) obtained from soil cores. Two plant species, acacia (Acacia saligna) and wheat (Triticum aestivum L.) were grown in a 1-m3 container on Silt Loam (Typic Torrifluvent) and on fine dune sand (Typic Torripsamment), respectively. Roots of both plants were measured periodically by the two methods. The MR observation tubes (MROT) were inserted, either vertically or at 45°. The correlation between the number of roots obtained by the MR and RLD was significant for the entire profile. However, an appreciable error in root estimation by the MR root observation method at the upper 10-cm soil might occur. No significant difference was obtained from MROT oriented vertically or at 45°. The differences between the correlation coefficients of the two methods were not significant, for both plants and soils, indicating that this correlation expresses the geometry of the two measurement systems, not affected by plant or soil types. We concluded that the MR method may be used as an in situ, non-destructive root measuring method with reasonable confidence.

Potassium, nitrogen, ammonium/nitrate ratio, and sodium chloride effects on wheat growth: I. Shoot and root growth and mineral composition

Abstract Fertigation with KNO3 as a means of reducing salinity hazards was tested with peanut (Arachis hypogaea) plants grown on dune sand, resulting in a reduction of plant growth and yield. The objective of this work was to study the interactions between N, K+ and NaCl as well as the effects of the NH4 +/NO3 ‐ ratio on vegetative and reproductive growth. Wheat (Triticum aestivum L.) plants were grown in polyethylene pots with fine calcareous dune sand with different proportions of NH4 + and NO3 ‐, under saline (60 mM NaCl) and non‐saline conditions. Three replicates were harvested at the beginning of flowering, and one was grown to grain maturity. NaCl reduced shoot dry weight in all the treatments. Increasing the NH4 + proportion in the total of 6 mM N in the nutrient solution, increased shoot dry weight, did not change nitrogen concentration in the dry mass but increased P percentage, either with or without 60 mM NaCl. The number of tillers produced in each treatment was correlated with dry matter yie...