SUMMARYFertilizer nitrogen did not delay tuber initiation by the potato variety King Edward in the field, but slowed the early growth of tubers. Later, N hastened tuber growth and the largest amounts prolonged it. Leaf and stem growth were increased by N from an early stage. Leaf area index (L) reached maxima of 2.5 to 3.0 with the largest amounts of N, and 1.0 with no nitrogen: L decreased after late July, faster with increased N, and only the largest amount prolonged the life of the haulm. N increased leaf area duration (D) by up to 125% in both years. D was 21% greater in 1964 than 1963, and net assimilation rate in August and September was larger; consequently mean yield was 50% more in 1964. Uptake of nitrogen and N % of dry matter were increased by increasing nitrogen. The N % of tuber dry weight remained constant or increased slightly from about 2 weeks after tuber formation, while N % of the leaves and stems decreased rapidly, and much N was transferred from tops to tubers. The 1964 results suggest that tuber growth depends on continued nitrogen uptake by the plant.P and K had small effects compared with those of N. K increased leaf area duration by 9% in 1963 and 3% in 1964, and yield by 11 and 8% respectively. P increased leaf area duration by 17% and yield by 9% in 1964. K had very small effects until the end of the season, when it prolonged the period of growth. P increased growth rates of all parts of the plant up to 4 weeks from emergence, and the differences in dry weight at that time persisted to maturity but did not increase.

The changeover from fertilizers containing calcium or ammonium sulphate to those containing little or no sulphur has led to the occurrence of sulphur deficiency in many areas of the world (McNaught & Christoffels, 1961). In the United Kingdom, it was thought that even in the absence of fertilizer sulphur, atmospheric inputs were sufficient to ensure an adequate supply for crops. Recent work in the north of Scotland has shown that this is not so, that many soils in the area are low in sulphur, and yield responses have been obtained following application of sulphur to grass (Soott et al. 1983; Scott, 1984). The purpose of the present experiments was to extend the work to cereals, in particular to examine the response to added sulphur of the grain yield of winter barley, and to measure the effect of sulphur on the chemical composition of plants.

S U M M A R YTwenty-five field experiments on barley were done at four sites from 1970 to 1975, with an additional site in 1975, comparing five rates of nitrogen application. The crops were sampled at c. 14-day intervals from about the four-leaf stage to maturity to follow changes with time in the dry weights of the constituent plant parts and to measure fertile tiller number, grain number per ear and grain weight. Some data have been selected from this body of information and regression analysis has been used to assess the possible importance of pre-and post-anthesis growth in determining the yield of barley. Ear emergence was taken as an approximate indicator of anthesis. Yield was closely related ( r = +0*96) and almost equal to the amount of dry matter accumulated before ear emergence for twenty-one of the experiments, with a regression coefficient of 0'95. I n two of the remaining experiments the regression coefficient was greater, 1-14; and smaller in the other two, 0.81. Plant population is also shown to affect the regression coefficient. Despite these anomalies grain yield was more closely related to plant dry weight at ear emergence than to the increase in weight after ear emergence ( r = +0-79). The increase in plant dry weight after ear emergence was frequently less than the yield of grain, suggesting that the plant can compensate for inadequate photosynthesis during grain filling. The result of this compensation is a reduction in straw dry weight. This implies that previously assimilated dry matter is transported to the grain, or that respiratory losses from the straw are not replaced by current photosynthesis. These observations suggest that yield may be limited by sink capacity rather than by photosynthesis after ear emergence. The main component of sink capacity, grain number per m2 was closely related to yield ( r = +o95) and is known to be determined at or before anthesis. Grain size was shown to be related to grain number per ear ( Y = + 0*99), suggesting that grain size is also, at least partially, determined at ear emergence. Therefore, all the yield components are determined, wholly or partly before ear emergence. I N T R O D U C T I O NA programme was initiated in 1969 to intensify studies on the responses of arable crops to management, soil type and environmental factors. I n particular, information was required concerning the factors which cause variation in response to fertilizer, and hence affect the validity of fertilizer recommendations. The first requirement of 405-422.

The effects of gibberellic acid (GA) and (2‐chloroethyl)trimethylammonium chloride (or Chlorocholine chloride, CCC), on growth of potatoes in pots were measured by growth analysis. GA was applied to the'seed piecesand CCC to the soil at emergence. GA accelerated emergence and stem growth but delayed leaf and tuber growth. CCC decreased growth of stems, leaves and stolons and caused tubers to form earlier. CCC did not modify the effects of GA. The initial effects of both regulators were reversed in the later stages of growth, so that yield and leaf area duration were unchanged.

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