RESPONSE OF ALFALFA TO CALCIUM LIGNITE FERTILIZER
T. Paré1, M. Saharinen1, M.J. Tudoret1, H. Dinel1, M. Schnitzer1 and D. Ozdoba2
1Eastern Cereals and Oilseeds Research Centre, Agriculture and Agri-Food Canada, Neatby Bldg, 960 Carling Ave., Ottawa, ON, Canada K1A 0C6
2Luscar Ltd, Specialty Products Division, 13044 Yellowhead Trail, Edmonton, Alberta, Canada T5L 3C1
Lignite is a low rank coal with low calorific value but potentially rich in humic substances (HSs), which are known to be non-polluting organic biostimulants particularly with regard to plant growth. They positively affect the nitrogen (N) and phosphorus (P) dynamics in soil1, stimulate nutrient uptake by plants2, 3, 4 by affecting some enzyme activities1, and so increase dry matter production2, 3, 4. Several authors assume that it is the functional groups (hydroxyl and carboxyl groups) contained in HSs which are mainly responsible for the responses obtained5, 6, 7, because they naturally chelate and transport cations and trace metals and make them more available to roots. These properties of HSs are utilized to produce organo-chemical fertilizers.
In the present study, we compared the effects of a calcium fertilizer produced from lignite to those of EDTA-Ca and calcium chloride (CaCl2) on the growth of alfalfa (Medicago sativa L.) and its nutrient uptake. We also compared the effects of the fertilizers when foliarly sprayed or applied on a growth substrate.
2 MATERIALS AND METHODS
2.1 Calcium Treatments
Three Ca treatments were used in this study: calcium chloride (CaCl2), EDTA-Ca and CaLF (a Ca fertilizer produced from lignite(Luscar Ltd)). Three levels of treatments were used : half of recommended rate of Ca for alfalfa (128.5 kg Ca ha-1), full rate (257 kg Ca ha-1) and full rate and half (385.5 kg Ca ha-1).These rates correspond to 78.3, 156.5 and 234.7 mg of Ca pot-1, respectively.
2.2 Greenhouse Experiment
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Alfalfa (Medicago sativa L., cv. Nitro) was used as test crop because of its high Ca requirements. Plants were grown in 1.6 L pots filled with 1.2 kg (dry mass basis) of a mixture of vermiculite and silica sand no. 24 (1:1 v/v). Each pot was sown with 10 g of seeds. The plants were watered with tap water and once a week with modified Hoagland solution without Ca. In addition, alfalfa was fertilized 17 days after sowing with half amount of N requirement (35 N kg ha-1 applied as NH4NO3), with full amount of P2O5 requirement (135 kg ha-1) and full amount of K2O requirement (275 kg ha-1). The rest of N (35 kg N ha-1) was applied 35 days after sowing as NH4NO3. Plants were first cut 35 days after sowing. Ca application was done in three stages, i.e, 35, 37 and 39 days after sowing. During each application, 50 mL of the appropriate Ca level was applied as foliar spray or on the substrate. Each treatment and the control (no Ca application) were replicated 5 times in a randomized complete block design. Plants were harvested 67 days after sowing and separated as shoots and roots.
2.4 Laboratory analyses
Shoots and roots were oven dried at 80°C for three days, weighed and ground to 60 mesh. They were digested with HNO3 + HClO4 + HF8 prior to ICP analysis for Ca, Mg, P and K. Nitrogen concentrations of shoots were determined as Kjedhal N. Because of the low dry masses of roots in some treatments, N and P in roots were not analyzed. Nutrient uptakes were calculated from concentrations and dry masses.
3 RESULTS AND DISCUSSION
3.1 Dry Masses
3.1.1 Applied as Foliar Spray
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CaLF and CaCl2 produced similar amounts of shoot dry masses (Fig. 1a). The highest shoot dry masses were obtained with the intermediate levels of CaLF (156.5 mg Ca pot-1) and the highest rate of CaCl2 (234.7 mg Ca pot-1). By contrast, EDTA-Ca application led to a decrease of shoot mass production. Shoot masses obtained with EDTA-Ca were on average 75 and 66% lower than those obtained with the application of CaLF and CaCl2, respectively (Fig. 1a). All levels of CaLF and CaCl2 produced similar amounts of root dry masses (Fig. 2a). By contrast, EDTA application decreased root dry mass by 64 to 83% compared to CaLF, and by 68 to 87% compared to CaCl2 (Fig. 2a). Alfalfa root dry mass production decreased with increasing rates of Ca applied as EDTA-Ca (Fig. 2a ). When foliarly sprayed, CaLF and CaCl2 produced similar whole plant dry masses, whereas EDTA-Ca led to a decrease of alfalfa whole plant dry masses (Fig. 3a).
3.1.2 Applied on the Substrate
When applied on the substrate, CaLF and CaCl2 produced similar amounts of alfalfa shoot dry masses (Fig. 1b). On the other hand, increasing EDTA-Ca rates led to a linear decrease of shoot masses. On the average, shoot dry mass was 62 and 71% lower when plant were fertilized with EDTA-Ca than with CaLF and CaCl2, respectively. CaLF and CaCl2 produced similar root dry masses, but on the average 67 % more root dry masses than did EDTA-Ca (Fig. 2b). Root mass reduction was dramatic and linear with the rates of EDTA-Ca applied. On the average, alfalfa whole-plant dry masses were, respectively, 88 and 101% higher when fertilized with CaLF and CaCl2 than with EDTA-Ca (Fig. 3b).
3.1.3 Comparison of both Modes of Ca Application
CaLF and CaCl2 produced more shoot masses when applied as foliar spray than when applied on the substrate, except at the lowest Ca rate, where the mode of application did not make a difference (Figs. 1a and b). Deleterious effects by EDTA-Ca on alfalfa shoot production were similar when this fertilizer was applied by spraying or on the substrate (Figs. 1a and b). Foliar spray of EDTA-Ca on average decreased root dry mass production by 39% compared to its application on substrate (Figs. 2 a and b). Applied as spray or on the substrate, CaLF and CaCl2 produced similar alfalfa root and whole-plant dry masses (Figs. 2a and b; 3a and b)
3.2. Ca Uptake
3.2.1 Applied by Spraying
For all fertilizers, alfalfa shoot Ca uptake increased with the rates of Ca applied (Fig. 1c). Calcium uptake by shoots was on average similar (ca. 94 mg pot-1) when plants were fertilized with CaLF and CaCl2 and, on the average 21% higher than EDTA-Ca (Fig. 1c). Calcium uptake by roots was similarly variable when CaLF and CaCl2 were sprayed on alfalfa plants (Fig. 2c) indicating that foliarly applied Ca was not translocated. By contrast, Ca uptake by roots decreased with increasing the rates of EDTA-Ca sprayed on plants (Fig. 2c), which was due to weak root growth. Whole-plant Ca uptake increased with the rates of Ca applied with CaLF and CaCl2, and there was no difference between the two fertilizers (Fig.3c). Except for a slight increase of uptake by whole plants following the foliar spray of 156.5 mg ca pot-1, EDTA-Ca did not stimulate any Ca uptake.
3.2.2 Applied on the Substrate
As shown in Fig. 1d, Ca uptake by alfalfa shoot fertilized with CaLF decreased with the increasing rates. By contrast, Ca uptake by shoots increased with increasing CaCl2 rates. Ca uptake by shoots following CaLF application was on the average 23% lower than that of plants fertilized with CaCl2. Shoots of alfalfa plants fertilized with CaLF on the average took up 17% more Ca than those fertilized with EDTA-Ca (Fig. 1d). On the other hand, Ca uptake by shoots of plants fertilized with CaCl2 was on the average 45% higher than those fertilized with EDTA-Ca. Root Ca uptake was similar (ca. 20 mg pot-1) when CaLF and CaCl2 were applied on the substrate. The application of the highest rate of both fertilizers led to a slight decrease of Ca uptake by roots (Fig. 2d). EDTA-Ca applied on the substrate drastically decreased Ca uptake by roots with increasing rates of Ca. Calcium uptake by whole plants was similar (95 mg pot-1) when CaLF and CaCl2 were applied on the substrates (Fig. 3d). EDTA-Ca application decreased Ca uptake by whole plants compared to CaLF and CaCl2.
3.2.3 Comparison of both Modes of Ca Application
Calcium uptake by shoots was higher when all Ca fertilizers were sprayed than when applied on substrates (Fig. 1c and 1d). Indeed, it was on average 44, 38 and 15% higher for CaLF, EDTA-Ca and CaCl2, respectively. Calcium uptake by shoots increased with the rates of Ca applied by spraying over those applied on substrates (Fig. 1c and d). Calcium uptake by roots was not affected by the application mode, but its uptake by whole plants was on average 29.6 % higher when sprayed than applied on the substrate (Figs. 2c-d and 3c-d).
3.3 Nitrogen, Phosphorus, Potassium and Magnesium Uptake
3.3.1 Applied by Spraying
Nitrogen uptake by shoots of alfalfa plants sprayed with CaLF did not vary with Ca rates applied (Table 1). However, N uptake by alfalfa shoots was higher with CaLF than with EDTA-Ca and CaCl2. Shoots of plants sprayed with CaLF and CaCl2 absorbed similar amounts of P, and on the average 32 and 27% more, respectively, than plants sprayed with EDTA-Ca (Table 1). Spraying CaLF on plants led to more K uptake by shoots than did spraying with EDTA-Ca and CaCl2. Shoots absorbed similar amounts of Mg when sprayed with CaLF and CaCl2, whereas Mg uptake following foliar spray with EDTA-Ca was considerably less (Table 1). Potassium absorption by roots decreased following applications of increasing rates of Ca for all fertilizers (Table 2), and was the lowest when EDTA-Ca was sprayed on alfalfa leaves. Magnesium absorption by roots decreased with Ca rates sprayed as EDTA-Ca, whereas this trend was not obvious with Ca rates applied as CaLF and CaCl2. Potassium absorption by all plants following CaLF application was on average 10 and 78% higher compared to applications of CaCl2 and EDTA-Ca, respectively (Table 3). Similarly whole plants absorbed more Mg following CaLF application than after CaCl2 and EDTA-Ca applications.
3.3.2 Applied on the Substrate
With substrate application of CaLF, N uptake in alfalfa shoots decreased with increasing rates; however, even at the highest application, N uptake was higher than with substrate application of CaCl2 or EDTA-Ca . Nitrogen average uptake by alfalfa shoots was 93 and 9% higher following CaLF application than following applications of EDTA-Ca and CaCl2, respectively (Table 1). Phosphorus uptake by shoots was similar when plants were fertilized with CaLF and CaCl2, but respectively, on average 13 and 24% higher than when fertilized with EDTA-Ca. Potassium uptake by shoots was not affected by the rate of CaLF applied. However, K uptake by shoots of plants fertilized with CaLF was on average 14% higher than when fertilized with CaCl2 (Table 1). EDTA-Ca application on the substrate decreased K uptake by half compared to the application of CaLF (Table 1). Except for EDTA-Ca which depressed K uptake by roots proportionally to the rates applied, similar amounts of this nutrient were absorbed by roots of plants fertilized with increasing rates of Ca applied as CaLF (Table 2). By contrast, K absorption by roots decreased when the highest rate of Ca was applied on the substrate as CaCl2. Magnesium absorption by alfalfa roots was lower following fertilization with CaLF than with CaCl2 (Table 2). The highest rate of Ca applied as EDTA-Ca considerably depressed Mg absorption by roots. CaLF application on the substrate stimulated more K absorption by whole plants than did EDTA-Ca and CaCl2 (Table 3). Similarly, whole plants in general absorbed more Mg when CaLF was applied on the substrate compared to EDTA-Ca, but 12% less than when CaCl2 was applied.
3.3.3 Comparison of both Modes of Ca Application
In general, foliar application of CaLF fertilizers stimulated more nutrient uptake in shoots compared to substrate application (Table 1). On the average, P and Mg uptake by shoots were, respectively, 14 and 36% higher when sprayed on leaves than when applied on the substrate (Table 1). Root K and Mg uptake were not affected by the mode of CaLF and CaCl2 applications, whereas the uptake of these two nutrients by roots was higher when EDTA-Ca was applied on the substrate than when sprayed on leaves (Table 2). Whole-plant Mg absorption was 28% higher when CaLF was sprayed on leaves than when applied on the substrate, whereas K absorption was not affected by the two modes of fertilization .
It is obvious from the results reported in this study that Ca fertilizer produced with lignite (CaLF) stimulated plant growth and nutrient uptake compared to the chemical fertilizer commonly used. Thus, our observations confirm earlier findings that HSs can increase dry matter production and nutrients uptake2,3,4. Plausible explanations for the effects of CaLF is that its functional groups complex Ca and so increase its solubility and availability to alfalfa plants. CaLF applied on substrates, could have also increased the permeability of alfalfa root membranes and so enhanced nutrients uptake2. According to Rauthan and Schnitzer2, HSs, particularly fulvic acid, contain structures that act like hormones which could facilitate the translocation of nutrients throughout the plants.
The data presented herein show that
1. Calcium lignite fertilizer and CaCl2 produced similar shoot, root and whole plant dry masses, which were much higher than when EDTA-Ca was applied.
2. Calcium uptake by shoots increased with Ca levels when foliarly applied. The levels and patterns of increase were similar when plants were sprayed with CaLF and CaCl2, and on average 22% higher than when sprayed with EDTA-Ca.
3. Calcium lignite fertilizer did not decrease N uptake, as observed with EDTA-Ca and CaCl2. N uptake by alfalfa shoots fertilized with CaLF was on average 91 and 20% higher than when fertilized with EDTA-Ca and CaCl2, respectively.
4. When sprayed on alfalfa leaves, CaLF stimulated more Mg and P uptake than did EDTA-Ca.
5. In general, foliar sprays of Ca fertilizers were more effective than substrate applications.
6. Calcium lignite fertilizer has a significant potential for not only correcting Ca deficiency, but also for stimulating the absorption of other nutrients.
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