The 15N isotope was used to compare the uptake and recovery of NH4 + and NO3 – nitrogen by ryegrass growing in soil under controlled simulated spring conditions when the temperature of the root was appreciably lower than that of the shoot. A preference was shown for NH4 + N over N03 – N, particularly at low soil temperatures. The limited uptake of NO3 – does not appear to be due to an inhibitory effect of the NH4 + ion. Ryegrass not only absorbed less N from NO3 – but also translocated a lower percentage of the total nitrogen taken up, to the shoots, the difference being greatest at low soil temperatures.

The results give increasing support for the recommendation that early spring nitrogen should be applied in the NH4 + form. However, the preferential uptake and translocation of NH4 + ions would be of agricultural importance only if it led to an increase in dry-matter production.

The ley-farming system (integrated cereal and livestock production in which cerealsrotate with self-regenerating pastures) is considered to be of great potential benefit to north Africa and west Asia. In the colder parts of this region (of which north Syria is typical) its application is limited by poor adaptation of commercial medic cultivars (mainly Medicago truncatula and M. littoralis). An extended selection programme hag identified M. rigidula as adapted to the soils and climate of the region but nothing is known of its adaptation to the ley-farming system itself.

An experiment which included 23 selections of M. rigidula and one each of M. rotata and M. noeana was conducted over 3 years during which herbage production, seed yield, and the fate of seeds were observed during the 1st year when pastures were established, the 2nd year when wheat was sown, and the 3rd year when the pasture regenerated. Of the 400–800 kg seed/ha produced in the 1st year an average of 87% remained in the soil in spring of the 3rd year. The weight of seed regenerating in the 3rd year varied from 30 to nearly 170 kg/ha, and herbage production, especially in winter, depended heavily on the number of regenerating seedlings. The most productive regenerating pastures produced nearly 2 t/ha of dried herbage by 1 January, and more than 6 t/ha for the whole growing season.

The results showed that there was sufficient residual and newly produced seed at the end of the 3rd year to be sure that subsequent regeneration would result in similar herbage yields in the 5th year, and that the pasture was assured of long-term persistence. The significance of this for livestock production is discussed, and it is concluded that the results should encourage further investigation of grazing management and socioeconomic factors seen as constraints to introducing the ley-farming system to north Syria.

Four experiments are reported which studied the effects of date of sowing on the development of winter and spring barley. The first three experiments (1979–80, 1980–1, 1982–3) were carried out at Trefloyne, Tenby and used the varieties Sonja (winter) and Jupiter (spring). The final experiment (1983–4) was carried out in Cambridge using the varieties Igri (winter) and Triumph (spring). A wide range of dates of sowing (August-June) was used and there were considerable differences in temperature between seasons.

In both Sonja and Igri, delaying sowing from August to mid-February reduced the number of mainstem leaves but further delay in sowing increased the number of leaves. In Jupiter, delaying sowing until late October had little effect but further delay consistently reduced the number of leaves. In Triumph, delaying sowing reduced final number of leaves over the whole range (October-May).

In all experiments rate of leaf emergence was characterized by long periods when leaves emerged linearly with time, despite considerable variation in temperature. The only consistent changes in rate of leaf emergence occurred shortly after each equinox, rates slowing in the autumn and increasing in the spring. Rates of leaf emergence were similar in different seasons and sites for similar periods despite differences in temperature.

Initiation of spikolet primordia proceeded linearly with time for most dates of sowing. For winter varieties rates of spikelet initiation increased with delay in sowing provided emergence occurred before the spring equinox. Further delay in sowing decreased the rate of spikelet initiation. In contrast in Jupiter and Triumph the rate increased with each delay in sowing. During periods of low temperature, rate of spikelet initiation slowed but frequently increased to faster rates in succeeding increasing temperatures. Such increasing temperatures had no effect on rate of initiation of later-sown treatments which had not experienced the low temperatures. Effects on spikelet initiation were found when no effects on leaf emergence could be detected.

Initiation of spikelet primordia in all varieties appeared to begin when a fixed number of leaves (different in some varieties) had emerged and end when a fixed number of leaves were left to emerge. Delaying sowing in winter varieties until February and in Jupiter over the whole range reduced the number of leaves emerging during spikelet initiation and was the developmental mechanism through which large differences in date of sowing became small differences in date of anthesis (and grain maturity).

Attempts to relate development to temperature were unsuccessful and the major influence on development appeared to be daylength. Number of emerged mainstem leaves was the most consistent measure of development over sites, seasons and varieties and for winter varieties was influenced by the direction of change of daylength at emergence. Two positive linear relationships between number of leaves and daylength at emergence were found for the periods from summer to winter solstice and from spring equinox to summer solstice. The slope of the latter relationship was greater than the former. For the period from winter solstice to spring equinox a negative linear relationship between number of leaves and daylength at emergence was found. In Triumph number of leaves decreased with decreasing daylength in the autumn and decreased further with increasing daylength. The effects in Jupiter were less clear but there was evidence of the effect of both daylength at emergence and direction of change on number of leaves.

In view of the control of number of leaves exercised by daylength, close negative linear relationships between time from sowing to anthesis and date of sowing were found. The significance of the results for relating agronomic practice to development is discussed.

The major portion of nitrogen nutrition of flooded rice is met through the mineralization of organic forms of N present in soil. This is true even when fertilizer nitrogen is added. The mineralization of organic matter under waterlogged conditions is governed mainly by the prevailing chemical and biological conditions. In recent years, attempts have been made to characterize the products of hydrolysis of soil organic nitrogen (Asami & Hara, 1970; Shinde, 1978; Subba Rao & Ghosh, 1981). Information on different fractions of nitrogen in waterlogged rice soils is scanty.

There is evidence from solution culture studies that ammonium nitrogen is taken up by grass preferentially to NO3-N at low temperatures (Clarkson & Warner, 1979). In addition NH4 ions are less subject to leaching losses or denitrification (Ryden, 1982). It has been speculated therefore that ammonium N could be the best form of nitrogen for early grass, especially in wet springs. Field experiments have studied the efficiency of different nitrogen forms at the first application over a number of years (McAllister et al. 1965; Van Burg, Dilz & Prins, 1982). The yield response has tended to be variable and may have depended on climatic and soil conditions. Investigations of climatic effects on fertilizer efficiency have often necessitated long-term field studies, but it is proposed that the importance of rainfall in particular could be investigated by means of a short-term irrigation experiment. This paper reports such an experiment using irrigation to simulate a wet spring while keeping other conditions the same for all treatments.

In the last two decades significant progress has been made in understanding the factors and processes affecting the K requirement of crops. Simultaneously analytical techniques to study the behaviour of K in soil have been developed, on the understanding that soil controls the supply of nutrients to crop plants by adsorbing and sometimes fixing nutrients. As in solution culture, the concentration of K in the soil solution governs the uptake of K by plants. The soil matrix serves as a reservoir from which the soil solution is replenished. Monitoring K status of the soil solution under fixed crop sequences can provide a useful basis for improving fertilizer recommendations. Kconcentrations in the soil solution have, therefore, been measured on a soil in which a number of crops have been grown in fixed annual sequences in field experiments.