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III. Nls,NH4+/NO3 - Ratios, and Plant Growth

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Figure 3. Ammonium-N and nitrate-N concentration in maize and rice soils. 0,without nitranitrate-N. Adapted from Prasad ef al. (1983).

pyrin; 0,with nitrapyrin; -, ammonium-N; -.-,

(1983) suggested the term "ammoniphilic plants" for species growing better with

NH,'. They maintained high concentrations (40-60 mg kg I NH,+-N soil) using NP (Fig. 3) and found that while maize plants suffered in growth, rice plants

did not (Table 111). Rice absorbed more N with NH4+,while maize absorbed less

N in the presence of higher concentrations of NH,'. They identified rice as an

ammoniphilic plant. Other species of ammoniphilic plants are known (Gigon and


Table 111

Plant Height and Dry Matter Accumulation in Rice and Maize Plants

Affected by N-Serve (NP) Treatment"



Plant height (cm)

Dry matter

(g per plant)






Without N-serve

With N-serve

LSD ( P= 0.05)













"Adapted from Prasad e t a / . (1983).



Rorison, 1972; Ingestad, 1976). In view of the growing concern over nitrate pollution of groundwater, there is a need for research on high-yielding ammoniphilic

cultivars of upland crop species.

Leaving aside the case of very high NH,+ concentrations resulting in toxicity,

Olsen (1986) cited several studies where the addition of NH,' to an all NO,system resulted in increased corn yields. Hageman ( 1 980, 1984) reviewed the effects of NH,' and NO,- nitrogen nutrition on plant growth and cited several experiments indicating that higher crop yields were obtained with a mixture of NO,

and NH,' than with either source alone. Ganmore-Neumann and Kafkafi (1983),

working with nutrient solutions varying in NO,- and NH,' concentrations, obtained optimal growth for strawberries with an equal ratio of NO,- to NH,'. Bock

(1987) observed a 19 to 47% increase in wheat yield with basal NO,--N +

urea + nitrapyrin compared to NO,--N alone. In two greenhouse studies, Camberato and Bock (1989) reported a 15- 18% increase in the grain yield of sorghum

when a higher NH,' concentration was obtained using urea and NP. Under field

conditions Israeli et ul. (1985) obtained a maximum yield of bananas when equal

ratios of NH,' to NO,- were present in the soil extracts. Bock (1986) found that

nutrient solution culture studies differed from those obtained under field conditions. Also, crop variety and stage of growth should be taken into account for

optimal utilization of the NH,+/NO,- ratio. Cosgrove et al. (1985), working

with snapbeans, found that the NO,- to NH,' ratio is critical for maximum

yields. Teyker and Hobbs (1992) reported that with coarse-textured soils and

slightly alkaline pH, an enhanced NH,' regime may be advantageous for the

growth of corn. They also observed that the differences in pH regimes between

the hydroponic and soil-based experiments may account for the contrasting results. In a study at Illinois (Gentry and Below, 1992), a continuous supply of

mixed NO,--N and NH,+-N increased corn yield by an average of 12% compared to NO,-N alone.

Shaviv er al. (1987) reported on the basis of pot culture experiments that wheat

and millet (Setaria italica) exposed to NH,' only with DCD produced lower

yields than those exposed to a mixture of NH,' and NO,-- with DCD. In wheat,

NH,' to NO,- ratios of 50/50 and 75/25 seem to be optimal. A 25/75 NH,+/

NO,- ratio produced the highest yield at maturity. Calcium and Mg2' uptake by

wheat and Mg2+uptake by millet were reduced as the proportions of NH,+ in soil

were increased. In the studies of Diest (1976) and Gashaw and Mugwira (1981).

maximum growth of wheat was obtained with a solution culture of 50: 50 proportion of NH,+ and NO,-. Based on data from a field study using DCD, Joseph

(1992) and Joseph and Prasad ( 1993a,b) reported that the optimum concentration

of NH,+-N in soil for maximum grain yield of wheat gradually decreased with

the age of the crop from 54.6 to 63.6 mg kg - I soil at 15 days after sowing (DAS)

to 22.7 to 26 mg k g - - ' soil at 30 DAS. In the case of NO,--N, its optimum


2 46


concentration for maximum grain yield increased with the age of the crop from

25.1 to 30 mg kg-I soil at 15 DAS to 31.6 to 34 mg kg-I soil at 45 DAS and

decreased thereafter.

Tsai et a/. ( 1 978) found that a greater amount of sucrose in corn (as measured

by I4C)was translocated from leaves to grain under NH,+-rich conditions, resulting in higher grain yield. Warren et al. (1975) found a reduction in “stalk rot”

incidence and increased yield of corn when N was kept as NH,’ for a longer

period with the help of NP.

As compared to NO3-, the assimilation of NH,’ in plants is not as well understood. According to Ivanko and Inguerson (1971) and Raven and Smith (1976),

NH,’ is almost completely converted to organic N in roots prior to translocation. Ammonium can be assimilated either through reductive amination of aketoglutarate with the glutamine dehydrogenase enzyme (GDH) system or by

incorporation into glutamate with glutamine synthetase (GS) and subsequent

transfer of the amide amino group of glutamine to a-ketoglutamate with glutamate synthetase (GOGAT) (Givan, 1979; Milfin and Lea, 1976; Srivastava and

Singh, 1987). Although increased activity of these enzymes does not necessarily

indicate their role in assimilation, increased GDH in the presence of NH,+ has

been reported in roots of pea, pumpkin, soybean, sunflower, and corn (Weisman,

1972; Magalhaes and Huber, 1989). GS activity in roots and shoots of rice is

reported to be higher than in the tissues of tomato and corn; in rice it increased

sharply in the presence of NH,+ (Magalhaes and Huber, 1989).

The NH,+/NO,- ratios and plant growth studies lead to the following conclusions: (1) The growth of most upland crop plants is best when both NH,’ and

NO3- forms of N are available for absorption; their relative amounts and ratios

vary with species, cultivars and age of plant; and (2) NIs can help in maintaining

NH,’ in soil in larger amounts and for longer periods of plant growth.


Experiments with NIs have been conducted with a fairly large number of crops,

including rice (Oryza sativa L.), corn (Zea mays L.), wheat (Triticurn aestivum

L.), grain sorghum (Sorghum bicolor L. Moench), sweet corn (Zea mays L. Rigosa), sugarcane (Saccharum oficinarum L.), bell pepper (Capsicum annum L.),

potato (Solanurn tuberosum L.), tomato (Lycopersicon esculentum Mill.), cotton

(Gossypium hirsutum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.),

sugarbeet (Beta vulgaris L.), spinach (Spinacia oleracea L.), lettuce (Latuca saliva L. var. Capitata L.), radish (Raphanus sativus L. var. radicula Pers.), cucumber (Cucumis safivus L.), cabbage [Brassica oleracea convar. Capitata (L) Alef

var. Alba DC], endive (Cichorium endivia L), turnip (Brassica rapa L.), and sev-



era1 grasses, including Lolium prenne L., Dactylis glomerata L., and Kentucky

bluegrass (Poa pmtensis L.) (Slangen and Kerkhoff, 1984; Waddington et al.,

1989). This chapter is restricted to major food and fiber crops of the world: rice,

corn, wheat, grain sorghum, potato, sugarcane, and cotton.



The wet conditions that exist during rice production and the preference of rice

for NH,+-N over NO,-N suggest that the application of NIs with NH4+-or

NH,+-producing fertilizers, such as urea, would be a sound N management practice. Prasad et al. (1986) suggested the use of NP for increasing N efficiency in

rice. Field experiments were conducted with NP, AM, and ST (Lakhdive and Prasad, 1970; Reddy and Prasad, 1977) and these clearly showed that on rice soils

with high percolation rates, nitrification inhibitors can be usefully employed for

increased rice yields and N efficiency. Nitrification inhibitors were specifically

effective in reducing N losses under alternate wetting and drying conditions frequently encountered in rice fields (Rajale and Prasad, 1972). Thomas and Prasad

(1987) reported that for direct-seeded rice, NP-blended urea produced 4.7 mg

grain ha ' compared to 3.7 mg ha I with urea. However, under similar conditions, DCD showed no advantage (Sudhakara and Prasad, 1986b).

Results from experiments conducted at different centers in Japan showed that

ammonium sulfate treated with NP increased rice yield by 15-20% over untreated

ammonium sulfate (Nishihara and Tsunyoshi, 1968). Similarly, in field tests carried out with AM in Japan, they showed that yields of transplanted as well as

direct-seeded rice were increased by the use of 5-6 kg ha-' AM along with ammoniacal fertilizers.

In the United States, Wells (1976) reported rice grain yield increases from the

addition of 1.12 and 2.24 kg h a - ' of NP applied with 67 to 178 kg h a - ' of

preplant-applied urea-N. In another study in Arkansas and Louisiana, no increase

in yield due to NP was recorded in 1977, but in 1978 there was a positive grain

yield response to NP (Touchton and Boswell, 1980). In Louisiana, Patrick et al.

(1968) reported no advantage with NP for rice. Wells ef al. (1989) summarized

results with DCD from Arkansas, California, Louisiana, Mississippi, and Texas.

DCD delayed nitrification and tended to result in rice grain yield increases compared to urea-applied preplant without DCD in drill seeding. In water-seeded continuously flooded rice, using DCD was advantageous only if the flood was delayed

for more than 14 days after urea application. At the International Rice Research

Institute, application of prilled urea with 10 or 15%DCD during the final harrowing produced lowland rice yields comparable to those with split applied prilled

urea without DCD (De Datta, 1986).

Bains et al. (1971) reported the effectiveness of neem (A. indica Juss) seed



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