What Happens to Nitrogen in Soils?

This publication explains the chemistry of nitrogen, the processes by which nitrogen is added to and removed from the soil, and methods of preventing nitrogen losses on agricultural lands

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the majorxonstraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg- 1 soil, leaf P content increased from 0.65 to 7.0 g kg-1 . Both A and DM had maximal values near 51.7 mg P kg- 1 soil, which corresponded to a leaf P content of 3.2 g kg- 1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (gs) tripled, and mean leaf internal CO2 concentration ([CC^];) decreased from 260 to 92 pL L~'., thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both Km, which is mathematically equivalent to quantum efficiency, and Vmax, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg-1 , with peak values between 4 and 5 g P kg-1 . Polynomial equations relating Km and Vmax, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny

Nitrogen and Phosphorus Uptake in Pearl Millet and Its Relation to Nutrient and Transpiration Efficiency

Depending on soil and rainfall characteristics, pearl millet [Penniseturn glaucum (L.) R. Br.] production in the Sahel can be limited by inefficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared the efficiency with which N, P, and water are used for growth under varied soil P and water availability. Millet was grown outdoors in semiarid West Texas using rain-sheltered pots of low pH, P-deficient sandy soil. Treatments consisted of four P levels (0–56 g−2) and two water treatments (stressed and not). Plant P concentration decreased strongly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and increased with water stress, but decreased with added P. Because of the effects of age, water availability, and P level on organ nutrient concentration, P-use efficiency (PUE) increased with age, decreased with water stress, and decreased with added P. Nitrogen-use efficiency (NUE) also increased with age and decreased with water stress, but tended to increase with added P. Shoot transpiration efficiency (WUFT) increased with water stress and added P, and so varied inversely with PUE throughout the growth cycle. Phosphate root uptake efficiency (PRE) was less sensitive than PUE to age, P availability, and water stress, because of the compensating effect of root growth; PRE was also positively correlated with WUET and yield. For crop improvement programs interested in increasing both P- and water-use efficiency, PRE is probably a better selection index than PUE

Liquid Reaction Apparatus for Surface Analysis

A design for a liquid reaction apparatus is described which allows surfaces prepared in ultrahigh vacuum (UHV) to be reacted with solutions of a wide pH range under dry nitrogen atmosphere and subsequently returned to UHV for surface analysis

Estimating pearl millet leaf area and specific leaf area

Leaf area and specific leaf area (SLA) are important parameters in many agronomic and ecological processes, but can be difficult and expensive to measure. This study was made to test simplified methods of estimating pearl millet [Pennisetum glaucum (L.) R. Br.] leaf area and SLA. Leaf length, maximum width, area, and dry mass data were obtained 85 kg of acidic, P-deficient Betis sand (sandy, silicious, thermic Psammentic Paleustalf) and were treated with four P levels and two water treatments (stressed and nonstressed). Individual leaf area was estimated non-destructively with the following equations(...

Pearl millet growth as affected by phosphorus and water

In outdoor pot trials near Nacogdoches, Texas in 1988, pearl millet was given 0, 1.15, 3.38 or 7.77 g P/m² with or without water stress conditions. Whole plant DM at final harvest, 84 d after emergence (DAE) increased from about 145 g/pot without P to 626 g with 7.77 g P without water stress and from 64 g without P to 220 g with 7.77 g P with water stress. There was a highly significant water treatment × P rate interaction in terms of plant DM at harvests 28-84 DAE. Grain DM at 84 DAE increased with increasing P rate but was negligible without P without water stress and with <3.38 g P under water stress conditions. Maximum whole plant production rates occurred between 42 and 58 DAE without water stress, increased from 5.0 g/d without P to 18.5 g with 7.77 g P, and between 28 and 42 DAE in water stressed plants, increasing from 1.3 g without P to 8.5 g with 7.77 g P. Growth rates of panicles and grain increased with increasing P rate and were greater without than with water stress. There were no clear effects of P rate or water stress on NAR or RGR

Soil Phosphorus Availability and Pearl Millet Water-Use Efficiency

The effects of P and water stress on transpirational water-use efficiency (WUET) of pearl millet (Pennisetum glaucum) cv. ICTP 8203 were studied in outdoor pot and growth chamber experiments. Plants were grown outdoors under semiarid conditions in covered pots containing 85 kg of acid, P-deficient Betis sand (sandy, siliceous, thermic Psammentic Paleustalf). Pots were given 0-7.77 g P/m² (equivalent to 0-70 kg P/ha), water stressed or not stressed, and plants harvested at 14-d intervals. Significant main and interactive effects on WUET due to P level, water treatment, and harvesting date occurred. The slope of the curve relating DM to cumulative transpiration increased with P level and water stress when data from all harvests were pooled. In the growth chamber, WUET of non-water-stressed plants ranged with increasing P level from 3.22 to 9.12 g/kg at 29 d after sowing (DAS) in pots containing 6 kg soil, and from 0.84 to 9.24 g/kg at 49 DAS in pots containing 18 kg soil. The ratio of leaf net photosynthetic rate to transpiration (WUEgas) at 500 µmol/m² per s photosynthetic photon flux density (PPFD) ranged from 1.88 µg/mg for plants receiving no P to 10.25 µg/mg for those receiving 0.31 g P/6 kg soil. Between PPFD levels of 500 and 2000 µmol/m² per s plants receiving no P increased WUEgas to only 3.60 µg/mg, whereas those receiving higher levels of P increased WUEgas to as much as 18.2 µg/mg. It was concluded that water supply in semiarid environments cannot be effectively managed for improved crop production without addressing soil fertility constraints

Recommandations specifiques d'engrais: Calibration et validation du module phosphore du modele NuMaSS

Fertiliser recommendations in Mali as well as in many other countries of West Africa were made according to Chaminade's method. For socio-economic reasons, correcting deficiency rates of major nutrients were vulgarized. These blanket recommendation, when applied, lead to a continuous soil nutrient mining. The objective of this research was to calibrate and validate the P module of NuMass. Laboratory incubations were conducted to calibrate the P buffering coefficients used by the P module. Rates of N, P and lime predicted by NuMass model, considered as specific recommendations, were compared to the blanket recommendations in the field in order to validate them. The buffer coefficients were inversely proportional to the clay content. The buffering coefficient of sandy soils of Cinzana/Mali (0.73) and Kollo/Niger P3 (0.63) were higher compared to the clayey soils of Longorola-bf (0.22) and Kollo/Niger (0.21). Generally, buffering coefficients obtained by laboratory incubation (0.60) tended to be lower than the estimated coefficient by the P module NuMass (0.67). The range of the used soil texture (1.5-54.6 % clay) showed that the buffering coefficients estimated by the P module of NuMass were correct for flooded soils. Grain yield of different trials and tests do not indicate the expected higher performance of specific recommendations of fertilisers from NuMass model compared to the used blanket recommendation (1624 and 1582 kg ha-1 of maize; respectively