Campbell, C.A.

Verma, G.P.

English

eCommons@USASK

Effect of soil moisture and method of N application on root growth of wheat

University of Saskatchewan Research Archive

- 219 -· EFFECT OF SOIL MOISTURE AND METHOD OF N APPLICATION ON ROOT GROWTH OF WHEAT C. A. Campbell*& G. P. Verma INTRODUCTION In a field experiment carried out by Dr. Verma in India there was an indication that splitting the N fertilizer application increased yield in a humid year but not in a dry year. The availability of some large weighing lysimeters at the Swift Current Research Station prompted us into setting up this study. Objectives were to determine (a) the relative efficiency of plant uptake of N applied in split applications)and to roots vs leaves and (b) how this might be influenced by soil moisture. MATERIALS AND METHODS Manitou wheat was grown on Wood Mountain clay loam (Mitchell et al., 1944) in weighing lysimeters (150 em deep x 40 em diameter). Four N treatments were combined factorially with three soil moisture regimes. Nitrogen treatments were (a) No N applied; (b) all N applied 2.5 em below the seed (basal); (c) 1/2 theN applied basal and 1/2 applied by foliar spray at tillering; and (d) 1/2 basal + 1/2 the N top-dressed at tillering. The moisture regimes were (a) rainfall only (dry treatment), (h) water added to adjust moisture to field capacity whenever depletion reached 10% of available moisture (medium·w~, and (c) moisture adjusted to field capacity whenever depletion reached 70% of available moisture (wet). The growing season rainfall in 1973 was 5.0 em which was much below the long time average of 16.57 em. There were three replicates per treatment; one of each replicate lysimeter was sacrificed for root determination at the end of the experiment. The N was applied in the form of urea at rates of 25 kg/ha for the dry treatment and 100 kg/ha where water was added. Phosphorus was applied at a rate of 100 kg/ha P20s to all treatments. Forty seeds of wheat were planted per tank and these thinned to 20 plants per tank after germination. The number of heads, the weight and N content of straw and roots were determined. (Because of grasshopper damage to grain only straw and root data were obtained). Roots were determined at maturity by cutting the cylinders lengthwise then sectioning the soil crosswise at 30 em intervals. The soil was ground, a subsample taken for moisture determination and the remainder soaked overnight in a Na2co3 solution to disperse it. The soil suspension was then washed through a nest of sieves and the roots collected and ovendried. RESULTS AND DISCUSSION The number of heads had been counted before the grasshopper damage "'"' 220 ~ occurred. The number of heads was increased to the same extent by the medium-wet and wet-treatments [compare to dry treatment (Table 1)]. Under dry conditions there was no effect of N application on the number of heads irrespective of the method of application. When water was added application of N increased the number of heads but there was no difference between method of N application. Table 1. Effect of soil moisture & method of N applicat~~n-~ on No. of heada/lysimeter ~ Rainfall only 10 to 100% field Treatment (dry) capacity (medium wet) Whole N basal 27 82 1/2 N basal + 1/2 foliart 24 78 1/2 N basal+ 1/2 top dressedt 25 80 No N applied 24 41 t . ~ '''''"" . ,.... , ,,,., .,, .... ,, ''''"''"' 70 to 100% field capacity (wet) 79 76 80 37 As expected, straw weight was directly proportional to moisture content (Table 2). However, root weight of the dry treatment was surprisingly greater than that of the medium-wet and as great as that of the wet treatment. Furthermore, in three of the four dry treatments, root weight was twice as great as straw weight (grain excluded). Some workers have reported greatest root growth under dry conditions while others report the opposite (Gardner, 1960). Hurd (1974) suggests that one reason why root growth in dry soils may appear better than growth in wet soils might be because of poor aeration associated with wet soils. Although this was possible in our study it is not consistent with our results since the weee ~est treatment outyielded the medium-wet treatment with respect to root weight. - 221 -~-, •. M<~> ,, "" ~'""'" .... '""' •• ' "'""'"" .. ,,., " Table 2 of straw & roots & on the straw/root ratio Rainfall only Treatments StraW* 10 to 100% field capacity Straw* Straw. Roo.ts root"""" Straw Roots root"-(g/lysfmeter) ratio (g/lysimeter) ratio Whole N basal 22 0.50 66 15 4.2 1/2 N basal + 1/2 foliar t 11 21 0.43 64 17 3.6 1/2 N baaal + 1/2 top dressed t 11 12 0.98 64 10 5.9 No N applied 6 14 0.49 26 10 2. 3 ~ ,..., .. .,,, ~ ·~""''"' """ ~- ....... 0><'"• .,.., dra11ina & foliar apray applied at tillering 70 to 100% field capacity ~ Straw Roots root (g/lysfmete'iT ratio 85 24 3.3 80 22 3. 7 82 10 8.5 32 10 3. 7 ~ Straw weight was increased by the addition of N but there was no difference between methods of application (Table 2). The same was generally true for root weight except where N was added 1/2 basal + 1/2 top dressed. These findings are not in keeping with those reported by others (Hurd, 1974) that split applications of N gave best yields and the most roots. The straw to root ratio was less than one in dry treatments and greater than one in wetter treatments. This indicates that under the dry conditions roots made more efficient use of the energy available to the plant than did the shoots. Similar observations have been made by others (Hurd, 1974). Generally; there was no consistent effect of N or method of N application ort straw/root ratio. Under dry conditions the roots were, in general, distributed evenly throughout the top 90 em of the profile with a significant propor-tion located below this depth (Figure 1). In the two wetter treatments, the major proportion of the roots were located in the top 60 em of the profile. Typical soil moisture distribution associated with the three moisture treatments are shown in Figure 2. Wiersum (1967) found that roots grew best where soil water suction was low. Singh (1952) reported that deeper roots are an advantage under conditions of high suction. The pattern of distribution observed in this study are therefore in keeping with the findings of Wiersum)l967 and Singh> 1952. It was also mn keeping with the fact that roots initially take water from surface layers but as suction increases in these layers they tend to take water from progressively deeper layers where suction is lower (Hurd, 1974). ~0 1-~ 25 ::11 "' "' 222 ~ o~-L-L-L~~~L-----~J_-L-L-L~------L-L-~~~-L----~~L-L-L-~J_---6 Vl ~ ::! 1-2 '" "' ~ 2~ a . ~ 0 -8 0: --' "' 1-0 1--u. 0 ~ ----------- NATURAL RAINfALL (CRY)--------------- ----~ Eigure 1 - Effect of method of N application and soil moisture on root distributions of Manitou grown in lysimeters 10 --- ---· -;W.P.--:E "' ~ o~~~~-L~~75rL~-.,~,2.-~ ,.. DEPTH {em) 0 c: 30 6 10 to 100"1. Field Cop. ------ f. C.- --- --~~ § 20, • • ~ ~ z 0 u w 0:: 10 -----W.P.-----~ o~--~3~7~~~7~~~~~,~12.-~ B DEPTH {em) :lE ..J 30 Natural Ralnloll 0 (/') -----f.C·--- -----20 f I f • f ___.....-I -10 .-- -----w.P.- ----112 DEPTH {em) Figure 2 - Soil moisture distribution - 22.3 -When both water and N were added the tendency was for over 50% of the roots to congregate in the top 30 em of the profile (Figure 1), but there was no differential effect of method of N application on root distribution. Bosemark (1954) has reported that increasing the N in soil caused increased root growth in the surface layers at the expense of depth of penetration. Percent N in straw and roots generally decreased with increasing soil wetness (data not shown). In general the addition of N tended to increase straw and root N but the method of N application had no differential effect. In conclusion, it would appear that under the conditions of this.study the three methods of N application had no differential effect on top or root growth, although all three methods generally increased growth compared to when no N was applied. Secondly, it was surprising to find that root growth under dry conditions was greater than under some of the more favoUl;able moisture regimes and also that under dry conditions root weight was .greater than straw weight. These findings would appear to require further verification. REFERENCES BOSEMARK, N. 0. 1954. The influence of nitrogen on root development. Physiol. Plant I: 497-502. GARDNER, W. R. 1960. Soil-water relationships in arid and semiarid conditions. In ."Plant Water Relationships in Arid and Semi-Arid Conditions." pp. 37-62. UNESCO Pub. Bucher, Lucerne, Switzerland. HURD, E. A. 1974. Root patterns in crops as related to water and nutrient uptake. pp. 167-235. In u.s. Gupta (ed.) Physiolog,cal Aspects of Dryland Farming. Oxford & IBH Publishing Co. New Delhi, India. MITCHELL, J., MOSS, H. C., CLAYTON, J. S., and EDMUNDS, F. H. i944. Soil Survey Rep •. No. 12. Univ. of Saskatchewan, Saskatoon, Sask. SINGH, K. 1952. Effect of soil cultivation on the growth and yield of winter wheat. IV. Effect of cultivation on root development V. Sci. Food Agr. 3, 514-525. WIERSUM, L. K. 1967. The mass-flow theory of phloem transport; a supporting caiculation. J. Exp. Bot. 18: 160-162. Comment: Concern was expressed over the method of split nitrogen applications as to whet~er this allowed the nitrogen enou~h time to b~ fully utilized by the crop. 

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Effect of soil moisture and method of N application on root growth of wheat

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