INFLUENCE OF IRRIGATION AND SUPPLY OF AVAIL- ABLE NITROGEN ON GROWTH AND NUTRIENT CONTENT OF SPRING WHEAT Armi Kaila and Paavo Elonen University of Helsinki, Department of Agricultural Chemistry Received February 6, 1970 The Law of Minimum states that the amount of plant growth is regulated by the factor present in minimum amount. In southern Finland this factor is often water, partic- ularly, when spring cereals are in question, and an improvement in the water supply during the critical period in June will increase the yield, provided no other factor will start to limit the growth. According to recent experience, on mineral soils this second factor may be nitrogen, if not more than the normal amount of fertilizer nitrogen is applied. It is obvious that an increase in the amounts of the minimum factors will have an influence on the metabolism of the plant and on the uptake of other nutrients. Thus, effects both on the quantity and on the quality of the yield may be detected. In order to study the dependence of growth and the nutrient content of cereals on the supply of water and nitrogen, samples of the aerial parts of spring wheat were collected at various stages of development from a field trial on irrigation and placement of nitrogen fertilizers. A part of the results of this trial have been treated from the point of view of the effect of irrigation on the uptake of nitrogen (Kaila and Elonen 1970); in the present study attention is paid to the effect of irrigation and supply of available nitrogen on the growth and the content of nutrients in the wheat plants. Experimental The field trial was carried out in the dry summer 1969 in cooperation with the Finnish Research Institute of Agricultural Engineering. The experimental field was in the neigh- bourhood of Helsinki, on silty clay soil of about pH 6 (in 0.01 M CaCl2 ) with 5 per cent of organic carbon and a satisfactory content of exchangeable potassium and »available» phosphorus. https://www.c-info.fi/en/info/?token=oGcoiRgx91Kq26_k.5YGsoOb4iYt-J0wRns3WMw.gZNPIKW_wu4LDfK-45YDs1rgWeTOw3XNYxHH0Zpt3fb4viYp-9gz0nJ94NhE3THiNk2tUwMO6FY-Ua0HgkO8VLDT4Cgq8qZc3RPe6HdZsDJ6nf9QAXlgqMImk7wxbJMtFpYnH6q6OkHGH9BsvH5q_pFvswWPB1Lpp9xWqESxqDTBOKA6aWPtA9k 206 As a basal dressing 800 kg/ha ofFinnish ammoniated PK-fertilizer was placed in rows at the depth of 8 cm. Thus, 16 kg N, 59 kg P and 100 kg K were applied per hectare. An additional amount of 120 kg N/ha was applied as a Ureaform-preparate, urea, or the Finnish ammonium nitrate limestone »Oulunsalpietari», all of them both as surface dressing or as placement. Since there was no significant difference in the effects of urea and Oulunsalpietari applied in the same way, the results obtained from these plots were combined in the present study. As surface application the effect of these fertilizers was distinctly lower than when they were placed. The response to ureaform remained rather poor, and it was equal in both manners of application. Thus, the supply of available nitrogen in this trial may be taken to represent four rates: Very low: only the basal dressing of 16 kg N/ha. Low: 120 kg/ha of N in ureaform. Good: 120 kg/ha of N in urea or Oulunsalpietari as surface dressing. Very good; placement of 120 kg/ha of N as urea or Oulunsalpietari. The experimental plant was »Ruso»-spring wheat, sown on May 8. It sprouted on May 20, came into ear on July 2, and was harvested on August 20. Plant samples were collected from nonirrigated plots, and from plots irrigated with slow sprinklers on June 9 and June 17,at both times with 30 mm ofdrainage ditch water. The sampling dates were June 16, June 30, July 21, and August 18. The shoots were cut from carefully measured strips at the end ofall the replicate plots. The sampling area was 0.84 m 2 and 0.50 m 2 in June, and 0.42 m 2 in July and August. In July and August the ears were cut from the samples and analysed separately. The grain samples were taken from the winnowed material. The samples were air-dried at room temperature, and ground in a Wiley mill. Total nitrogen was determined by the common Kjeldahl procedure. The total content of phos- phorus, potassium, magnesium and calcium was measured from acid ash solution: phos- phorus was determined by the ammonium vanadate molybdate method, potassium by an EEL-flame photometer, and magnesium and calcium by a Perkin-Elmer atomic absorption spectrophotometer. The results were treated with Duncan’s new multiple range test. Values of each sampling date marked by the same letter in the table do not differ at P = 0.05. Results The growth of spring wheat under different treatments was estimated on the basis of the amount of dry matter in the plant samples collected. These results are reported in Table 1 calculated to correspond to the amount of dry matter as kg/ha. It is of interest to note that on June 16, there was not yet any response to the 30 mm of irrigation water applied one week before this sampling date. At the end of the month, or about two weeks since the application of the second 30 mm of irrigation water, the yields of the irrigated plots contained 750 to 1000 kg/ha more dry matter than those of the nonirrigated plots, except when the supply of available nitrogen was very low. The positive effect of nitrogen on the production ofplant matter was apparent already on June 16. It tended to increase at the later stages of development, particularly on the irrigated plots. On these plots, the amount of dry matter produced when the nitrogen 207 Table 1. Dry matter of spring wheat, kg/ha. Irrigation Supply of available N mm Very low Low Good Very good June 16 Shoots 0 800 840ab 900 ab 1080d 30 850ab 830ab 920bc 1020cd June 30 Shoots 0 2550a 2620a 2920ab 3250bc 30 + 30 2660a 3620 C 3670c 4170 d July 21 Straw 0 3310 a 3690a 4020ab 3950ab 30 + 30 3930ab 4570 b 5770c 6300c Ears 0 1210m 1320™ 1430» 1370™ 30 + 30 1320™ 1410» 1680° 1720° August 18 Straw 0 2210a 2570 ab 2750abc SlOO 1^ 30 + 30 3110bc 3550c 4760d 5380 d Ears 0 2830 1» 3360™ 3670™ 4050» 30 + 30 4070» 4180" 5590° 6120° supply was very good was on June 16, June 30, July 21, and August 18 about 20, 36, 53, and 61 per cent higher, respectively, than the corresponding yields on the plots with very low nitrogen supply. The positive effect of irrigation appears to be markedly higher with good or very good supply of available nitrogen than with low or very low supply. On July 21, e.g., the increase in the total dry matter yield by irrigation was less than 20 per cent when the supply of nitrogen was very low or low, but 37 per cent when the nitrogen supply was good, and more than 50 per cent when it was very good. On the basis of the results of August 18, the response to the placement of 120 kg/ha of soluble fertilizer nitrogen was 2200 kg/ha of dry matter, the effect of irrigation alone corresponded to 2140 kg/ha, and the combined effect of both these treatments resulted in an increase of 6460 kg/ha in the dry matter production. The positive interaction of water and nitrogen supply is obvious. The nitrogen content of the plant samples (Table 2) gives a slightly different picture. The nitrogen percentage tended, of course, to rise with the improvement in the supply of available nitrogen, but the effect of irrigation was more complicated on the nitrogen content than on the dry matter yield. In June, the samples collected from the irrigated plots contained, in most cases, significantly more nitrogen than the corresponding samples of nonirrigated plots. In the July samples, there is no more any significant difference be- tween the nitrogen content of the corresponding samples. In the ears, there is some tend- ency to lower nitrogen content in the irrigated samples, and this is statistically significant in the samples of August 18, except when the nitrogen supply was very low. In the straw samples this difference is significant only with very good nitrogen supply. Table 2. N in spring wheat, per cent of dry matter. Irrigation Supply of available N ram Very low Low Good Very good June 16 Shoots 0 2.71“ 2.86“ 3.21 b 3.85' 30 2.85» 3.30b 3.95' 4.30d June 30 Shoots 0 1.53» 1.67b 1.86' 2.08 d 30 + 30 1.68b 1.85' 2.33' 2.50f July 21 Straw 0 0.85» 0.99b 1.32' 1.56' 30 + 30 0.95»b 0.92»b 1.38'd 1.47d' Ears 0 2.20™ 2.34™“ 2.50"° 2.58° 30 + 30 2.21™ 2.21™ 2.38™“ 2.46”° August 18 Straw 0 0.38“ 0.43“ 0.52b 0.69' 30 + 30 0.35“ 0.36“ 0.55b 0.58b Ears 0 1.78™ 2.00" 2.47 P 2.72