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Improving water productivity is one important strategy for addressing future water scarcity, which is driven particularly by increasing human population and potential climate and land use changes. Although an understanding of water productivity is required to develop improved water management strategies, little is known about it in irrigated systems of the sub-Saharan Africa. This study assesses the physical crop water productivity at farm and scheme scales for two distinct systems: a medium and small reservoir in semi-arid environment of the Upper East Region in Ghana. The study concludes that water productivity for the study reservoirs is low, and that potential for improvement exists through improved irrigation water management and agronomic practices.

One month of incubation experiment was implemented to evaluate the changes of phosphorus fraction in inorganic P (Pi) and organic P (Po) induced by phosphorus fertilizer (KH2P04),cow manure ( manure) and CaC03 (lime). A 0.5 kg oven-dried weight of arable layers of Latosol from Darmaga, Bogor was used in this study. The rates of manure were 0, 12.5 and 25 ffha, lime were 0, 1, 3 times the CaC03 equivalent required to neutralize exchangeable aluminum amounting to 0, 3.01, 9.03 t/ha respectively and the rates of phosphorus fertilizer in KH2P04 were 0, 40 and 80 kg Plha. All treatments increased resin-Pi (biologically available P). Application of phosphorus fertilizer also increased NaHC03-Pi which is also included as biologically available PI whi!e manure and lime only tended to increase this fraction. Phosphorus fertilizer and manure application were able to enhance NaOH-Pi (moderately resistant P related to AI-P and Fe-P ) but lime did not affect it.Phosphorus fertilizer, manure and lime increased HCI-Pi (moderately resistant P related to Ca-P).The changes of NaHC03-Pi to resin-Pi and P immobilization by microorganism, which was indicated by the increase of NaHCOrPo (readily mineralizable), can be attributed to the decrease of NaHC03- Pi. The increase of NaOH-Pi by phosphorus fertilizer and manure indicated that the complexation of P fixation sites by PO6 and organic acids likely had occurred.

Remobilization of leaf nitrogen during the seed filling stage was investigated in relation to patterns of leaf abscission with three pigeonpea genotypes (Cajanus cajan) of different maturity duration (extra-short (ESD), short (SD), and medium (MD)). Leaflet abscission (trifoliate leaf) started from the bottom of the plants. The life span of defined leaf layers in the canopy differed among the genotypes and tended to be longer toward the top of the plants. At harvest, the leaf layer close to the pod-bearing top of the plant had a survival rate of 75% and 31% in ESD and SD pigeonpea, respectively, indicating that a large number of leaves in ESD was not entirely exploited for nutrient redistribution to the seed. Net remobilization of nitrogen from leaves during the reproductive stage was obtained from an above-ground plant budget for N and amounted to 35, 47, and 37% of the pod''s requirement for N in ESD, SD, and MD, respectively. The amount of nitrogen in the defined leaf layers decreased exponentially with time, and the rate of N loss was calculated from the regressions in terms of half-life. For most of the layers half-life was longest in ESD pigeonpea indicating slower abscission and remobilization compared with both other genotypes. It is suggested that the efficiency to remobilize leaf nitrogen for seed development is related to the pattern of leaf abscission in pigeonpeas, and that SD pigeonpeas remobilize leaf N more efficiently than ESD and MD

Urea is the main form of fertilizer nitrogen applied to wetland rice. As part of an effort to evaluate the efficiency of nitrogen fertilizers, conventional urea and modified urea products such as sulfur-coated urea (SCU), urea supergranules (USG), and sulfur-coated urea supergranules (SCUSG) were compared with ammonium sulfate on an Aquic Tropudalf at the experimental farm of the International Rice Research Institute (IRRI) in the Philippines. The sulfur-coated materials were prepared in the laboratory and were not completely representative of commercial SCU. Two experiments were conducted in the wet season (1978, 1979) and one in the dry season (1979). All fertilizers were labeled with 5% or 10% excess15N so that the fertilizer-N balance at two or three sampling times during the growing season could be constructed and the magnitude of N loss assessed. The SCU, USG, and SCUSG were applied at transplanting, and the whole dose of nitrogen was15N-labeled. The urea and ammonium sulfate applications were split: two-thirds was broadcast and incorporated at transplanting, and one-third was broadcast at panicle initiation; only the initial dose was15N-labeled.

Data pertaining to grain yield, yield parameters, and N uptake during different periods of rice growth, in three field experiments, were subjected to the statistical procedure of path coefficient analysis. The observed grain yield response to the applied fertilizer N was predominantly reflected in an increased panicle density and spikelet number. The 1,000‐grain weight was only slightly influenced by N fertilization. Since both panicle density and spikelet number are known to be largely determined within 70 days after transplanting (DAT), N uptake during this ‐period was found to be critical to achieve a maximum grain yield response to applied N. The K uptake during 0–40 DAT correlated positively with panicle density, whereas absorption of N during 40–70 DAT determined both panicle density and spikelet number. Since N uptake during 0–20 DAT exerted a significant positive influence on grain yield through increased panicle density, the basal application of a part of fertilizer at the time of transp...

In an effort to provide an explanation for the reported variability in fertilizer N efficiency from deepplaced urea on flooded rice, a set of controlled experiments was conducted to evaluate the effect of water percolation on fertilizer loss and plant uptake from15N labeled urea supergranules. Three soils of different texture (silt loam-clay) were subjected to various percolation rates (0–20 mm/day) while planted to rice which was harvested after approximately 40 days.

On alkaline coarse-textured soils (Psamments) of Punjab, India, urea is applied after the irrigation event to minimize leaching and denitrification loss. However, placement of urea on the wet surface of alkaline soils promotes NH3 volatilization. This experiment compared (i) urea, (ii) urea plus dicyandiamide (DCD), a nitrification inhibitor, (iii) urea plus phenylphosphorodiamidate (PPD), a urease inhibitor, and (iv) potassium nitrate (KNO3) applied before or 20 h after the irrigation event. Grain yield of wheat (Triticum durum L. var. DWL5023) and N use efficiency were observed in a 2-yr study. During the first year all of the fertilizers were N labeled. Potassium nitrate gave the highest yield and maximum N recovery by the crop indicating that leaching and denitrification were not significant loss mechanisms. Grain yield was increased from 3.6 to 4.4 Mg ha and loss of urea-N was reduced from 42 to 16% by applying urea just prior to irrigation compared to following irrigation. DCD did not alter the effect of fertilizer timing with respect to irrigation on N recovery or wheat yield. Urea applied with PPD yielded 0.4 Mg ha more than urea alone when applied on wet soil. This suggests that NH3 volatilization was the major N loss mechanism. This study suggested that for higher N use efficiency and grain yield of wheat, urea should be topdressed before the irrigation event on the coarsetextured soils. Additional Index Words: wheat, nitrogen-15 balance, dicyandiamide, phenylphosphorodiamidate, potassium nitrate. View complete article To view this complete article, insert Disc 5 then click button8