Knowledge to increase the microbial biomass nitrogen (MBN) as a bulk of free-living microbes in paddy soil is limited. The potential benefit of these microorganisms was evaluated, in this study, under different nitrogen sources and two paddy soils. The results revealed that pots treated with organic matter recorded the maximum value of the total N uptake and MBN, followed by the Urea treated pots. Pots amended with sludge exhibited a higher microbial N forming ability than those amended with straw compost under both soils. But ammonium concentration in soil increased with straw compost application. Under fresh soil treatment, microbial N uptake rate and proportion of plant nitrogen derived from microbial nitrogen sources () were higher than autoclaved soil. A positive correlation was found between the and the total N in rice shoot in both soils. Finally, we can say that MBN was governed not only by the soil nitrogen content but also by the type of the nitrogen source. The addition of sludge to fresh soil increased total MBN and consequently could be indirectly beneficial to rice production especially in poor soils. Thus, soil microbes contribute to plant growth by serving the available nitrogen during the season.

Two desert wadies of contradictory ecological conditions were studied. The water factor seems to be the most critical ecological factor in determining the type of vegetation as well as its richness. In Wadi Gimal, of extremely dry conditions (both climatic and edaphic) a typical xerophytic community dominated by Zilla spinosa, Pulicaria undulata and Cassia italica was identified, together with a less xeric (but more tolerant to salinity) community of Tamarix aphylla — Limonium axillare exist in the deltaic part of the wadi near the Red Sea coast. In Wadi El‐Miyah, of fairly rich water resources, 3 communities were identified the species composition of each reflects different degrees of aridity which is related to local physiography in the wadi coarse. These communities are: 1. Community of Salsola delileana — Francoeuria crispa, 2. Community of Acacia raddiana — Pergularia tomentosa and, 3. Community of Zygophyllum coccineum — Pulicaria undulata.

The response of elements of the water balance of olive plants grown in desert farms to partiall irrigation was investigated. A m o n g these are transpiration, leaf relative water content, the number of leaves carried by trees and the osmotic pressure of the leaf sap. The proper time for irrigation and suitable ways of its application were also studied. A method of applying subsurface irrigation, to minimize direct evaporation from the soil, is described. The results show a slight decrease in transpiration rate of irrigated plants compared to the controls. However, an increase in the number of leaves as a result of irrigation was found to result in increased total transpirational water loss. An inverse relation seem to exist oetween the a m o u n t of foliage and its relative water content in periods ot no active growth. This relation is reversed during active growth. The osmotic pressure of leaf sap also responded inversely to changes in leaf water content during periods of inactive growth. On time of active growth, relative water content and osmotic pressure rose more or less together. The results indicate t h a t among the methods of irrigation studied, summer subsurface irrigation is more favourable for the water balance of the plant.

Soybean (Glycine max) was grown with root systems divided between adjacent cartons containing nutrient solution or soil. By adding polyethylene glycol (Carbowax 6000) to reduce solute potential or withholding water to reduce soil matric potential until water absorption from that side stopped, the root xylem water potential could be ascertained. Carbowax appeared to increase root resistance. An imbalance technique is described with which soil moisture contents of adjacent containers were followed individually. The patterns of water absorption obtained following repeated additions of water or addition of CaCI2 solutions to one side indicated soil hydraulic conductivity became limiting at a soil water potential of -2 bars. A high concentration of CaCl2 added to one side greatly reduced transpiration and produced severe plant injury. With part of the root system developing in nutrient solution, growth of roots into and water absorption from soil were slow; however, reduction of solute potential in the solution side greatly increased water absorption from the soil side.Divided root systems have been grown in solutions to investigate the uptake of mineral elements (8,9,21,23), to check the effects of solute concentration on salt and/or water absorption (5, 7, 21) and on water potential (4') of leaves and solute potential (48) (19), to compare the effects of inorganic and organic solutes (21), and to determine average (day + night) 4' of roots (7). Micropotometers have been devised and used on various sections of isolated single roots grown in solution to investigate both water and ion absorption and the effects of various osmotica on these processes (3-5, 10-12, 25).Divided root systems in soil have been used to study cross transfer of minerals (1) and flooding injury (16); however, most work has been directed toward investigation of root growth into, water loss from roots to, and mineral absorption from dry soil (2,13,15,26,27).The use of divided root systems in determining root 4' and following patterns of water absorption in different situations is described here.