Abstract:
THE EFFECT OF NITROGENOUS FERTILIZER ON WOOL PRODUCTION AND LIVEWEIGHT OF MERINO WETHER SHEEP IN SOUTH WESTERN AUSTRALIA H. LLOYD DAVIES*, E. A. N. GREENWOOD* and E. R. WATSON* Summary Three levels of ammonium sulphate (0, 280 and 840 kg per hectare) were applied as a split dressing each year at emergence and in August to a pasture of Bromus mollis L. and Trifolium subterraneum L. (var. Dwalganup), at Kojonup in south Western Australia for five years. The pasture was continuously grazed with medium Peppin Merino wether sheep at 8.65 and 12.36 sheep per hectare. In the first year, the ammonium sulphate increased liveweight of the sheep in autumn and winter and annual wool production. In later years, sheep, grazing plots top-dressed with ammonium sulphate, lost more weight from December to May and produced less wool per head than sheep on control (no nitrogen) plots. I. INTRODUCTION There is little critical information other than that of Tayler and Rudman (1960), Moloney and Murphy (1963) and Wedin, Donker and Martin (1965)) comparing the effect of application of nitrogenous fertilizer and nitrogen from a legume on animal production on a long term basis. In southern Australia, in the areas where sown pastures are used, reliance is traditionally placed upon a leguminous plant as a so'urce of nitrogen for pasture production. The work reported here was an investigation into the role o f fertilizer nitrogen upon animal production. II. MATERIALS AND METHODS This work was carried out at the C.S.I.R.O. Research Station, 'Glen Lossie,' Kojonup, Western Australia. The climate of the area has been described b y Rossiter (1961). An area of virgin country, a mixture of Kojonup sandy loam and Balgarup sandy loam (Smith 1948)) was cleared in 1956 and cultivated in 1961 and sown with Trifolium subterra:neum L. var. Dwalganup (25 kg/hat) and Bromus m&s L. (7 kg/ha) . There were three nitrogen treatments applied as ammonium sulphate (21 v. N) to the sward: -no ammonium sulphate. -280 kg/ha of ammonium sulphate; 140 kg/ha soon after emergence in autumn. and 140 kg in August. * C.S.I.R.O., Division of Plant Industry, W.A. Regional Laboratory, Nedlands, Western Australia. 'r 1 hectare = 2.47 acres. 222 -840 kg/ha of ammonium sulphate; 420 kg/ha applied soon after emergence and 420 kg in August. There were two stocking rate treatments: 8.65 sheep/ha and 12.36 sheep/ha. The stocking rate effect was obtained by altering plot size, each plot being grazed by six medium Peppin Merino wether sheep. The same sheep remained on the plots for the duration of the experiment, from November 1961 to August 1965, the sheep only coming off the plots for shearing. There tias no supplementar y feeding. The ammonium sulphate and stocking rate levels were factorially combined in three randomized blocks. Sheep were weighed at intervals of three weeks throughout the experiment and shorn each August. III. RESULTS (a) Iiveweight change The liveweight changes of the sheep for each year of the experiment (Figure 1) show the typical pattern of wether sheep on an unsupplemented pasture in a Mediterranean environment. The sheep usually began to gain weight three or four weeks after the opening rains in the autumn and continued to gain weight until December-January, although there was no further pasture growth after early November. The sheep lost weight from January onwards, the loss in weight becoming more severe in March until the new season's growth was sufficiently advanced to meet the requirements of the sheep for liveweight gain. In 1961-62, the sheep on the high nitrogen treatments, shown in Figure 1 , started to gain weight on June 21, those on the low nitrogen treatment started gaining weight on July 12 and those on the control treatment on August 2. In 1962-63, a false break in late March 19613 caused all sheep to gain weight for three weeks. All groups then lost weight until June when all groups commenced gaining weight. In 1963-64, the figure shows quite clearly the inverse relationship between the liveweight of the sheep and the level of nitrogen applied. There was a late (mid-June) break in this year which affected pasture growth and hence sheep liveweight. In 1964-65, the nitrogen effects were similar to those of 1963-64, but the earlier ` break of season' rains ensured liveweight gain earlier in the year. After the initial summer on the plots (December 1961 to April 1962) there was, at each level of nitrogen, a clear effect of stocking rate upon liveweight per head. The sheep being depastured at the lower stocking rate either gained weight more rapidly on green feed or lost weight more slowly on dry feed. However, there were instances after the second year (1962-63) when sheep on the higher stocking rate and at the Zower level of nitrogen fertilization were heavier than those being depastured at a lower stocking rate where the pasture had been top-dressed` with nitrogenous fertilizer. (b) Wool production Table 1 summarises the effect of nitrogenous fertilizer and stocking rate Nitrogenous fertilizer increased wool producupon wool production per head. tion in 1962 but not afterwards. FIGURE 1. Fig. 1. -Effect of different rates of nitrogenous fertilizer on liveweight of sheep at two stocking intensities. TABLE 1 of Wool Production (kg, greasy) per head and per hectare for each yem nitrogen x stocking rate experiment the Least Significant Differences for comparisons P<O.OS 0.24 kg P<O.Ol 0.31 kg P<O.OO 1 0.40 kg * P<O.O5 ** P<O.Ol * * * P<O.OOl TABLE 2 Botanical composition of pasture on offer in October, 1963 There was a highly significant interaction between years and nitrogen which arose from the positive effect of nitrogen upon wool production in the first year of the experiment, and the small or negative effect in the later years. (c) Pastures The botanical composition for October 1963 is shown in Table 2. The the first summer in Table value of extreme dominance of brome grass in the high nitrogen treatments after year implies a feed of low nutritive value for the sheep during the period. This is supported by the data on chemical composition shown 3. The addition of nitrogenous fertilizer did not affect the nitrogen brome grass over the summer. IV. DISICUSSION The results from this experiment suggest that caution must be applied before the use of nitrogenous fertilizers on sown pastures for wool production and maintenance of liveweight in wether sheep is recommended. The interesting negative effect of nitrogenous fertilizer upon animal production after the first year of the experiment is probably either a reflection of an interaction between nitrogenous fertilizer and stocking rate and grazing management or the direct effect of spring applications upon bontanical composition. This effect does not, however, explain the positive response in liveweight and TABLE 3 Chemical composition of the grass and clover on offer to the sheep in nitrogen x stocking rate experiment, March 1965