Soil & Tillage Research, 9 (1987) 79--89 79 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

E F F E C T O F S O I L M A N A G E M E N T O N R A I N - F E D W H E A T I N N O R T H E R N I N D I A . I I . N U T R I E N T U P T A K E , P L A N T G R O W T H A N D Y I E L D

P.D. SHARMA and C.L. ACHARYA

Department o f Soil Sciences and Water Management, Himachal Pradesh Agricultural University, Palampur-176062, H.P. (India)

(Accepted for publication 3 June 1986)

ABSTRACT

Sharma, P.D. and Acharya, C.L., 1987. Effect of soil management on rain-fed wheat in Northern India. II. Nutrient uptake, plant growth and yield. Soil Tillage Res., 9: 79--89.

Field experiments were conducted to study the effect of soil management practices such as zero cultivation (ZC), conventional cultivation (CC), CC + surface-applied pine needle mulch (CC + M), deep ploughing (DP) and inter-row compaction (IRC) on nutrient utilisation and growth of rainffed wheat (Triticum aestivum L.). The soil was a silty clay loam with compact sub-surface layers and classified as Alfisol, Typic Hapludalf. The con- centrations of NO3-N and NH4-N in soil, in general, were less under CC + M and DP and more under ZC and IRC compared to CC. Despite the low availability of N under CC + M and DP, the plants did not suffer from nitrogen stress compared to other treatments. In fact, the total uptake of N by plants at different growth stages was significantly higher than CC, except for DP during early growth. The total uptake of P and K was also sig- nificantly higher under CC + M than CC. However, under DP it was not always significant- ly higher than CC. Mulching resulted in significantly higher dry matter yield than CC at tillering, stem elongation and heading. DP also produced significantly higher dry matter yield than CC at heading. ZC and IRC behaved similar to CC in terms of nutrient uptake and dry matter yield. The grain yield of CC + M during 1981 and in CC + M and DP during 1982 was significantly higher than the remaining treatments.

INTRODUCTION

R e s t r i c t e d r o o t s y s t e m s c a n r e s u l t in r e d u c e d n u t r i e n t a b s o r p t i o n a n d g r o w t h o f p l a n t s ( D r e w , 1 9 7 8 ; P e t e r s o n e t al . , 1 9 8 4 ) . R o o t g r o w t h m a y b e a f f e c t e d as a r e s u l t o f an i n a d e q u a t e s u p p l y o f w a t e r , s u b - o p t i m a l soi l t e m p e - r a t u r e a n d m e c h a n i c a l i m p e d e n c e ( C h a u d h a r y a n d S a n d h u , 1 9 8 3 ) . S u c h un- f a v o u r a b l e c o n d i t i o n s f o r t h e g r o w t h o f w h e a t r o o t s a n d p l a n t s c o u l d b e o v e r c o m e b y t h e a d o p t i o n o f m a n a g e m e n t p r a c t i c e s p r o v i d i n g f o r c o v e r o n t h e soi l s u r f a c e (B lack , 1 9 7 0 ; Aase a n d S i d d o w a y , 1 9 8 0 ; W i l h e l m e t al . ,

0167-1987/87/$03.50 © 1987 Elsevier Science Publishers B.V.

80

1982; Chia, 1982; Chaudhary and Chopra, 1983), and deep ploughing (Reddy and Dakshinamurty, 1971; Kaddah, 1976). However, these practices may cause reduction in the available N content of soil (Anderson and Russell, 1964; Unger, 1979; Bakajev et al., 1981), possibly by encouraging its downward movement with water. In that situation, the nitrogen supply might become critical to the plants. It would be worthwhile, therefore, to evaluate these practices in terms of nutrient utilisation, especially nitrogen and plant growth under our situations in India where the aforesaid problems exist. The practice of zero tillage, which is less labour intensive compared to conventional cultivation and avoids the problem of clod formation, is also worth its evaluation. Inter-row compact ion is another practice favoured for inducing more vertical growth of roots to draw upon the water in deeper soil layers.

MATERIALS AND METHODS

Field experiments were conducted at the experimental farm of the Himachal Pradesh Agricultural University, Palampur, India, during 1980--81 and 1981--82 to study the effect of different soil management practices on nutrient uptake, growth and yield of rain-fed wheat. The soils have a pH value of 5.6, cation exchange capacity of 14 meq per 100 g and an organic carbon content of 0.75% in the surface (0--15-cm) layer. The soils are gen- erally low in available N and P.

The treatments, replicated seven times in 5 × 2.4-m plots, included zero cultivation without crop residues (ZC), conventional cultivation (CC), CC + surface applied pine needle mulch at a rate of 10 t ha -1 (CC + M), deep ploughing upto 30--35-cm depth (DP) and inter-row compaction (IRC). The details of experimental layout and soil physical properties have been described in the preceding paper (Bhagat and Acharya, 1987).

To determine the amount of available soil nitrogen under different management practices, soil samples were taken with a tube auger midway between the rows for every 15-cm soil layer down to the 90-cm depth. The samples were taken in triplicate before and 10, 25 and 40 days after fer- tiliser application at flag leaf stage. The amount of N O r N and NH4-N in moist soil was determined by the method outlined by Onken and Sunderman (1977).

To determine the dry matter yield and uptake of nutrients at different growth stages, viz., tillering, stem elongation and heading, plant samples were taken from a 50-cm row length of every third row in the plot from three replicates. The samples were oven-dried at 65°C to constant weight. The samples were analysed for total N, P and K by the methods of micro Kjel- dahl, molybdovanadate yellow colour and flame photometry , respectively (Jackson, 1973). In addition, grain and straw samples derived from the three replicates were analysed for total N, P and K.

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RESULTS AND DISCUSSION

Nitrogen availability

From long-term fertiliser experiments conducted on these soils for the last 14 years, it has been shown that there is very little contribution of nitrogen due to mineralisation at any time and plants could hardly sustain growth under control conditions (Yaduvanshi et al., 1981). As such, NO3-N and NH4-N in soils would vary largely in response to fertilisation. The concentra-

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tions of NO3-N and NH4-N before and at different intervals after fertilisation are shown in Figs. 1--3 for the first year (1980--81). The second year results were similar to those for the first year. The contents of NO~-N and NH4-N at various depths and at different intervals were invariably low under CC + M and DP treatments and higher under ZC, in comparison with CC treatment. The IRC treatment generally had more concentration in the surface 0--15- cm layer, but less in sub-surface layers compared to the CC treatment. The greater drop in the concentrations of NO3-N and NH4-N under CC + M and DP treatments could be due to more leaching of nitrogen with rain water, as suggested by a wetter soil moisture regime (Bhagat and Acharya, 1987) and higher infiltration rates (Acharya and Bhagat, 1984) under them. The reduc- tion in NO3-N content under mulching has also been reported by Anderson and Russell (1964) and Bakajev et al. (1981) in a humid climatic environ- ment. Anderson and Russell (1964) ascribed the reduced NO3-N availability under straw mulch compared to bare soil to reduced soil temperatures. How- ever, the reduced temperatures may not be the only factor causing repression in the NO3-N contents of soils under mulches in our study because the NO3- N contents under pine needle mulch, which generally had higher soil tem- peratures, were still low compared to the bare soil having relatively low soil temperatures. The wet regime under mulches might be a factor reducing N availability by affecting its downward flux. The higher concentration of NO3-N and NH4-N under ZC and IRC treatments could be expected due to less movement of N with rain water, brought about by an increase in the bulk density of surface layers (Bhagat and Acharya, 1987).

Nutrient uptake

In spite of low availability of N under CC + M and DP treatments, the N contents of plants at different growth stages and grain did not differ signif- icantly from other treatments. This suggests that plants under the practices supporting large root systems (Bhagat and Acharya, 1987) do not suffer from nitrogen stress even under low available N conditions. In fact, the total uptake by plants, calculated on a unit area basis, was significantly higher under CC + M than CC treatment at tillering, stem elongation and heading and at heading under DP (Table I). The total uptake by grain was also sig- nificantly higher under the CC + M and DP treatments than CC treatment. For instance, the total uptake under CC + M during 1980--81 was higher by about 39, 37 and 39% than CC treatment at stem elongation, heading and harvest (grain), respectively. The uptake was even more contrasting during 1981--82.

Although the ZC and IRC treatments had higher availability of nitrogen than CC + M, the uptake values were significantly lower. The ZC and IRC treatments also had decreased root growth. Peterson et al. (1984) also re- por ted less N uptake by winter wheat plants having a restricted root system than plants having a large root system, when adequate N was supplied in

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both situations. In their experiment, the plants with a large root system con- tained about 34% more N than the plants with a confined root system.

The P and K contents of plants at different growth stages did not differ significantly among treatments, but during 1980--81 the concentration in grains was significantly higher under CC + M than the other treatments. Moreover, the total uptake by plants at different growth stages, and by grain was significantly higher under the CC + M treatment than CC (Tables II and III). For example, P uptake at stem elongation, heading and harvest (grain) during 1980--81 was higher by 53, 50 and 68%, respectively, than for the CC treatment. Similarly, K uptake was higher by 47, 49 and 44%, respec- tively. The DP treatment also showed a similar trend in uptake by plants at stem elongation and heading and by grain. However, the significant increase over CC treatment was only during 1981--82, for P at all growth stages and for K at heading and harvest (grain). Enhanced uptake of P and K by wheat plants having large root systems compared with confined root systems has also been reported by Peterson et al. (1984). In their study, the concentra- tion of P in shoots of plants with a confined root system was higher than that of plants with a large root system, although the total uptake of P per gram of below-ground dry weight for plants with large root systems was al- most 40% more than that in plants with restricted root systems. Similarly, Apple and Butts (1953) at tr ibuted the increase of P in pole beans to a larger root system.

The higher nutrient utilisation under CC + M and DP treatments was prob- ably due to enhanced root growth that could have facilitated more removal of nutrients (Nielsen and Humphries, 1966; Terman et al., 1976; Chaudhary and Sandhu, 1983). The relatively more efficient utilisation under mulching could be expected because of an enlarged, fibrous and more active root sys- tem conditioned by relatively better moisture and thermal regimes (Black, 1970; Wilhelm et al., 1982; Bhagat and Acharya, 1987). The fibrous root system would have more nutrient absorptive surface area per unit root mass. There is sufficient evidence as to the importance of higher soil temperatures in increasing the uptake of nutrients by plants under mulching, possibly by influencing the growth and activity of roots (Nielsen and Cunningham, 1964; Case et al., 1964; Power et al., 1964; Knoll et al., 1964; Gingrich, 1965; Sutton, 1969; Terman et al., 1976). Although, no observations were made to determine if differences existed in the production of root hairs under different practices, the increased oxygen availability under mulch would increase the number of root hairs and possibly could enhance nutrient fluxes into wheat plants. Itoh and Barber (1983) found that root hairs con- tr ibuted to P uptake in six species, including wheat.

There was strikingly higher nutrient utilisation under mulching during the early growth phase, i.e., tillering, relative to CC treatment. The uptake of N, P and K was higher by 128, 259 and 274%, respectively, over the CC treat- ment during 1981--82. The higher soil moisture and temperatures and re- duced temperature fluctuations near the soil surfaces under mulch, resulted

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in an environment conducive to enhanced nutrient uptake during early growth. Unlike CC + M, the DP treatment showed no better nutrient utilisa- tion than the CC treatment during early crop growth. However, the effect became pronounced with the advancement of growth when roots started proliferating in the deep ploughed layers, thereby increasing nutrient uptake.

Plant growth and yield

The CC + M treatment had significantly higher dry matter yield than the CC treatment at different growth stages (Table IV). The dry matter yield in- creased by 207, 110 and 68% over CC treatment at tillering, stem elongation and heading, respectively, during 1981--82. Similarly, it increased by 46 and 57% over CC treatment at stem elongation and heading, respectively, during 1980--81. The DP treatment also produced significantly higher dry matter yield than CC at somewhat later stages of crop growth, i.e., at stem elonga- tion and heading during 1981--82 and at heading during 1980--81.

The grain yield (Table IV) in the CC + M treatment during the year 1981 (LSD at 5% = 333) and in CC + M and DP treatments during the year 1982 (LSD at 5% = 395) was significantly higher than the remaining treatments. During 1981, the grain yield in the DP treatment was significantly higher than the CC, ZC and IRC treatments. Treatments of ZC and CC and ZC and IRC produced statistically equal grain yields; however, the CC treatment pro- duced significantly higher grain yield than the IRC treatment. During 1982, the ZC, CC and IRC treatments, produced grain yields statistically at par.

The increased growth and/or grain yields of wheat have been reported earlier under management practices providing for cover on soil surface (Black, 1970; Bond et al., 1971; Aase and Siddoway, 1980; Bakajev et al., 1981; Chia, 1982; Wilhelm et al., 1982; Chaudhary and Chopra, 1983), and deep ploughing (Drezgic and Jevtic, 1963; Reddy and Dakshinamurty, 1971; Kaddah, 1976). Increased plant growth and grain yield under these treat- ments was a consequence of better physical soil environment that enhanced gross root growth and its activity and in turn shoot growth, owing to in- creased water and nutrient uptake. Besides water and nutrient uptake func-

TABLE IV

Dry mat ter yield of wheat plants at different growth stages and harvest under various managemen t practices

Trea tment Tillering Stem elongation Heading Harvest (grain) ( g m : ) ( g m : ) ( g m : ) ( k g h a ~)

1981--82 1980--81 1981--82 1980--81 1981- 82

15 133 111 324 347 2575 1950 20 198 163 346 361 2700 2300 62 290 342 5,15 607 3460 3450 20 198 249 442 556 3050 3225 18 131 184 315 409 2285 1925 18 38 62 50 143 333 395

ZC CC CC+ M DP IRC LSD (1%)

1908--81 1981--82

87

tions roots can markedly influence the activities of the shoot (Torey, 1976), thus affecting coordinated development of plants. Root-derived growth sub- stances are known to influence shoot growth, including the outgrowth of lateral shoots (Skene, 1975). Carmi and Heuer (1981) reported that restric- t ion of root growth in bean plants growing in very small pots leads to the development of dwarf plants. Similarly, Peterson et al. (1984) reported that winter wheat plants with restricted root systems were significantly reduced in size as measured by number of leaves and culms per plant, main stem height and final dry weight per plant. Their results suggested that restricted rooting will in itself limit the growth of plants, when supplied with adequate nutrients and water.

Strikingly more growth under CC + M at tillering relative to CC treatment revealed bet ter development of plants during the early stage of growth which otherwise may not be possible owing to frequent drought and sub-optimal soil temperature conditions during this period. The DP treatment produced significantly higher dry matter yield than the CC treatment at a somewhat later stage of crop growth. Thus, the significant benefit of DP became evi- dent only at a later stage when roots started proliferating in deep ploughed layers. The dry matter yield of CC, ZC and IRC treatments at different growth stages and harvest did not differ significantly.

CONCLUSIONS

Results indicated that the plants under the mulching and deep ploughing treatments did not show nitrogen stress despite the low availability of nitrogen. In fact, the dry matter product ion and the total uptake of nitrogen under these treatments were higher than conventional cultivation, except for deep ploughing during early growth. Similarly, the total uptake of P and K was also significantly higher under mulch than under bare soil. This suggests that plants may meet their nutritional requirements well, even under low fer- tility situations, with soil management practices that encourage an enlarged root system. The other practices like zero cultivation and inter-row compac- tion behaved similar to conventional cultivation. Since zero cultivation re- quires no elaborate tillage and nutrient utilisation, growth and grain yield are comparable to conventional cultivation, the former could be more eco- nomical than the latter.

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