Relative effectiveness of organic and inorganic nutrient sources in improving yield, seed quality and nutrient uptake of canola ()
1. INTRODUCTION
Any nutrient(s) limiting in soil can cause a substantial reduction in crop yield. In the Canadian Prairies, most soils are deficient in available N, many are low in available P, and some contain insufficient amounts of available S (like many Gray and Dark Gray soils in the Parkland region) and K for optimum crop growth and yield, especially under organic agriculture [1-3]. Nutrient deficiencies in crops can be prevented by using organic and inorganic nutrient sources. Chemical fertilizers, because of their huge yield response, easy availability, and convenient transportation and application, are very attractive and commonly used to enhance crop production [4-7]. However, it is possible that the long-term use of increased amounts of only chemical fertilizers may degrade soil structure and deteriorate productive capacity of soils [8,9]. On the other hand, sole application of organic nutrient sources may not be able to maintain and synchronize the required supply of nutrients to the growing plants for optimum crop production, because of relatively less quantity of plant-available nutrients and more time needed for mineralization to release nutrients for effective plant uptake [10-17]. Judicious/proper use of organic and inorganic nutrient sources is important to decrease the sole dependence on chemical fertilizers for sustainable high crop production by minimizing nutrient losses to the environment and optimizing nutrient use efficiency [18-23]. Integrated/combined use of organic and inorganic amendments or chemicals may be a way to ensure high sustainable soil productivity, fertility and quality, and environmental quality [22,24-30].
In the semi-arid region of the Canadian Prairies, maintaining soil fertility is an important production issue facing organic agriculture [2]. The N deficiency in soils on organic farms can be minimized by growing N-fixing legume crops in the rotations as grain or green manure crops [31-37]. However in soils deficient in available P, K, S or other essential nutrients, the only alternative is to use external nutrient sources because synthetic fertilizers/chemicals cannot be applied to prevent nutrient deficiencies and increase yield in organic crops. Manure/ compost and some other organic amendments can provide these nutrients, but often there is not enough manure to apply on all farm fields, or the high cost of transportation of low nutrient content manure makes their use uneconomic [38-44]. On such soils, rock phosphate fertilizer, elemental S fertilizer, gypsum, wood ash (a waste product of forest industry) or other amendments may be useful to correct deficiencies of these nutrients.
The information on the relative comparisons of organic and inorganic nutrient sources in preventing nutrient deficiencies in the same experiment is lacking, especially in the Parkland region of Canada. The objective of this study was to determine the relative effectiveness of organic and inorganic nutrient sources (amendments/ chemicals), and their combined applications in preventing nutrient deficiencies in crops, and increasing crop yield, seed quality and nutrient uptake.
2. MATERIALS AND METHODS
The 4-year (2009 to 2012) field experiment was established in the spring of 2009 on a Gray Luvisol (Typic Haplocryalf) loam soil near Star City, Saskatchewan. Soil at this site has shown severe S deficiency in canola in previous years [45], and significant increase in forage yield of timothy from S application as well as non-significant increase in forage yield of timothy from P application [46]. Some characteristics of soils used in this experiment are presented in Table 1. Precipitation in the growing season (May, June, July and August) at the nearest Environment Canada Meteorological Station (AAFC Melfort Research Farm) is given in Table 2.
A randomized complete block design was used to lay out the treatments in four replications. Each plot was 7.5 m long and 1.8 m wide. There were 31 treatments (except Treatments 27, 30 and 31 missing in 2009, and Treatments 24 and 25 missing in 2012): 1. Control (no amendment); 2. Compost @ 20 Mg·ha−1; 3. Wood ash – fine @ 2 Mg·ha−1; 4. Alfalfa pellets @ 2 Mg·ha−1; 5. Alfalfa + canola meal pellets @ 2 Mg·ha−1; 6. Distiller grain (wheat) − wet @ 2 Mg·ha−1; 7. Distiller grain (wheat) − dry @ 1 Mg·ha−1; 8. Thin stillage @ 20,000 L·ha−1; 9. Glycerol @ 1 Mg·ha−1; 10. Fish food additive @ 1 Mg·ha−1; 11. Triple super phosphate (0-45-0) @
Table 1. Some characteristics of soil in spring 2009 at initiation of the field experiment at Star City, Saskatchewan.
Table 2. Growing season monthly and total precipitation for the four site-years, and average 30-yr average precipitation and temperature at Star City, Saskatchewan.
20 kg·P·ha−1 + ammonium nitrate (34-0-0) @ 80 kg·N·ha−1 + potassium sulfate (0-0-51-17) @ 20 kg·S·ha−1; 12. Penicillium bilaiae + 80 kg·N·ha−1 + 20 kg·S·ha−1; 13. Rock phosphate granular (International Compost) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 14. Rock phosphate finely-ground (International Compost) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 15. Rock phosphate granular (BC Mines) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 16. Rock phosphate finelyground (BC Mines) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 17. Gypsum @ 20 kg·S·ha−1 + 80 kg·N·ha−1 + 20 kg·P·ha−1; 18. Rapid release elemental S (RRES) @ 20 kg·S·ha−1 + 80 kg·N·ha−1 + 20 kg·P·ha−1; 19. Glycerol @ 1 Mg·ha−1 + 80 kg·N·ha−1; 20. Wood ash − fine @ 2 Mg·ha−1 + 80 kg·N·ha−1; 21. Distiller grain (corn) − dry @ 1 Mg·ha−1; 22. Treatment 15 + Penicillium bilaiae; 23. Treatment 16 + Penicillium bilaiae; 24. Rock phosphate + humates granular (BC Mines) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 25. Treatment 24 + Penicillium bilaiae; 26. Rock phosphate [powder] (BC Mines) @ 20 kg·P·ha−1 + 80 kg·N·ha−1 + 20 kg·S·ha−1; 27. N + S − 80 kg·N·ha−1 + 20 kg·S·ha−1; 28. Wood ash − granular @ 200 kg·ha−1 (applied side band); 29. Wood ash − granular @ 200 kg·ha−1 (applied side band) + 80 kg·N·ha−1; 30. N + P − 80 kg·N·ha−1 + 20 kg·P·ha−1; and 31. N only − 80 kg·N·ha−1. Estimated amounts of N, P, K or S applied annually in various treatments are presented in Table 3. In 2009, N only (Tr 31), NP (Tr 30) and NS (Tr 27) treatments were not applied. In 2012, we could not obtain rock phosphate + humates granular fertilizer, so Treatments 24 and 25 did not receive any amendments in 2012. Amendments were broadcast on surface and then incorporated to about 10 cm soil depth a few days prior to seeding. Plots were seeded with a double-disc press drill at 17.8 cm row spacing. Data were collected on seed and straw yield, and on concentration of total N, P, K and S in seed and straw. Seed yield was determined by combine harvesting a 7 m long and 1.2 m wide strip in each plot. Seed and straw samples were oven dried (60˚C), and analyzed for total N [47], total P [48], total K [49] and total S [50] to calculate total N, P, K and S uptake in seed and straw by multiplying seed or straw yields by the concentrations of these nutrients in seed or straw.
The data on each parameter were subjected to analyses of variance (ANOVA) using GLM procedure in SAS [51]. The least significant difference at P ≤ 0.05 (LSD0.05) was used to determine significant differences between treatment means.
3. RESULTS
3.1. Weather Conditions
The growing season precipitation (GSP) was near long-term average in 2009, with slightly lower than average precipitation in May and slightly higher than average precipitation in August (Table 2). In 2010 and 2012, the GSP was much higher than average (especially in June), and relatively cooler air temperatures in the summer. In 2011, the GSP was below average (especially in May during seeding season and in August during seed formation/filling), with relatively cooler air temperatures and wet conditions in June, and relatively warmer/hotter air temperatures and dry moisture conditions in late July
Table 3. Estimated amounts of N, P, K or S applied annually in different treatments at Star City, Saskatchewan.
and August.
3.2. Seed and Straw Yield
Combined application of N, P and S chemical fertilizers (NPS) produced considerably greater seed yield of canola compared to the unamended control in all four years (Table 4). In treatments with only organic amendments, thin stillage produced the highest seed yield in all years, and it was similar (or even slightly greater in some years) to the NPS balanced fertilization treatment. Compared to the control, fish food additive and distiller grain dry of wheat in 2009, 2011 and 2012, distiller grain dry of corn in 2009 and 2012, compost in 2011, and alfalfa pellets in 2011 and 2012 produced significantly greater seed yield. There was also a moderate increase in seed yield with compost and alfalfa pellets in 2009, alfalfa +
Table 4. Seed yield of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
canola meal pellets in 2009, 2011 and 2012, with wood ash fine in 2009 and 2012, with distiller grain wet of wheat in 2011 and 2012, and distiller grain dry of corn in 2011, although not significant. This suggests the potential of these treatments possibly with long term repeated annual applications. There was a slight reduction in seed yield of canola from wood ash granular, glycerol, distiller grain wet of wheat and distiller grain dry of corn in a few years.
In treatments where chemical fertilizers were also applied in addition to organic amendments, application of N fertilizer increased seed yield substantially in wood ash fine treatment in all years. This suggests that wood ash fine was lacking in N, and its application along with N fertilizer supplied the nutrients lacking in this soil (mainly S, and also possibly P to some extent). Application of N fertilizer also increased seed yield in wood ash granular treatment but mainly in 2009, 2011 and 2012, and to a lesser extent than wood ash fine. The poorer performance of wood ash granular than wood ash fine was most likely due to poor availability and/or possibly unequal distribution of nutrients to canola plants from sparse application of wood ash granules in relation to canola plants/roots. There was no beneficial effect of glycerol on seed yield, and application of N increased seed yield in glycerol treatment but only in 2009 and 2012 and seed yield was usually much less than gypsum + N + P or NPS fertilizer treatment, suggesting the lack of N, S, and/or P in this treatment for optimum crop growth.
Compared to the unamended control, there was a considerable reduction in canola seed yield in 2010 and 2011, and a slight/moderate reduction in 2012, when only N fertilizer was applied without any sulphate-S. Application of P along with N (NP) resulted in some increase in seed yield compared to the N alone treatment, butnot significantly better than the control. The combined application of N (as ammonium nitrate) + P (as triple super phosphate) + S (potassium sulphate) chemical fertilizers (NPS) produced considerably higher seed yield of canola compared to the control. This suggests that seed yield of canola can be improved significantly by using balanced NPS fertilization/nutrition on this soil, extremely deficient in plant-available N and S, and possibly containing insufficient amount of available P for optimum yield, especially with canola being a particular S-sensitive crop. Application of rapid release elemental S (RRES), along with N + P fertilizer, usually produced seed yield similar to gypsum + N + P treatment. Seed yields with both gypsum and RRES treatments were significantly greater than with the N only treatment, but slightly less than with the NPS treatment in some years.
Application of N + S, in combination with finelyground or powder rock phosphate, produced seed yield greater than that with granular rock phosphate, and it was similar to or only slightly lower than the NPS treatment, but only in 2011. This suggests the positive contribution of finely-ground or powder rock phosphate in increasing availability of P and improving seed yield of canola in the third growing season. The lower seed yield obtained with granular rock phosphate and/or Penicillium bilaiae, in combination with N + S, than the NPS treatment in all years suggests the poor performance of granular rock phosphate and/or Penicillium bilaiae in increasing P availability and improving seed yield of canola. The response trends of straw yield to all organic and inorganic amendments were generally similar to seed yield in most cases, with only a few exceptions (Table 5). For example, unlike seed yields, the straw yields were similar between NP and NPS treatments in 2011, and also there was some increase in straw yield with only N treatment compared to no amendment control in 2012.
3.3. Protein and Oil Concentration in Seed
Treatments including only organic amendments (i.e., without any chemical fertilizers) usually resulted in little or no significant effects on protein concentration in canola seed, although protein concentrations were increased or decreased in a few cases compared to the no amendment control treatment (Table 6). For example, there was an increase in protein concentration with thin stillage, fish food additive or distiller grain in 2011 or 2012, and a reduction in protein concentration in canola seed using compost and wood ash treatments in 2010 and 2011. In treatments where chemical fertilizers were also applied, in addition to amendments, protein concentration in canola seed increased or tended to increase with glycerol, gypsum, RRES or wood ash treatments in some years. There was no beneficial effect of any amendment + chemical fertilizer treatment on oil concentration in canola seed, but there was a tendency of decrease in oil concentration in canola seed in the N, glycerol + N and NP treatments in 2010, 2011 and 2012, and in the NS or NPS treatment in 2011 (Table 7).
3.4. Nutrient Uptake in Seed + Straw
The response trends of uptake of total N, P, K and S in seed and straw to organic and inorganic amendments were generally similar to the corresponding seed and straw yields, respectively (data not shown). The results on uptake of total N, P, K and S in seed + straw of canola are presented in Tables 8-11. In treatments with only organic amendments, total N uptake in seed + straw with thin stillage was similar (or even slightly higher in some cases) to the NPS balanced fertilization treatment (Table 8). Compared to the control, fish food additive in all four years, distiller grain dry of wheat in 2009, 2011 and 2012, distiller grain dry of corn in 2009 and 2012, and alfalfa pellets in 2012 produced significantly greater total N uptake in seed + straw. There was also a moderate increase in total N uptake in seed + straw with compost and alfalfa pellets in 2009 and 2011, alfalfa + canola meal pellets in 2009, 2011 and 2012, with wood ash fine in 2009 and 2012, with distiller grain wet of wheat in 2011 and 2012, and distiller grain dry of corn in 2011, although not significant. There was a slight reduction in total N uptake in seed + strawof canola from wood ash granular, glycerol, distiller grain wet of wheat and distiller grain dry of corn in a few years.
Table 5. Straw yield of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
In treatments where chemical fertilizers were also applied, in addition to organic amendments, application of N fertilizer substantially increased total N uptake in seed + straw with wood ash fine treatment in all years. This indicates that wood ash fine was lacking in N, and its application along with N fertilizer supplied the nutrients lacking in this soil (mainly S, and also possibly P to some extent), resulting in increased N uptake. Application of N fertilizer also increased total N uptake in seed + straw with wood ash granular treatment but mainly in 2009, 2011 and 2012, but to a lesser extent than with wood ash fine. The poor performance of wood ash granular
Table 6. Protein concentration in canola seed with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
compared to wood ash fine was most likely due to poor availability and/or possibly unequal distribution of nutrients to canola plants from sparse application of wood ash granules in relation to canola plants/roots. There was no beneficial effect of glycerol on total N uptake in seed + straw. Application of N fertilizer increased total N uptake in seed + straw with glycerol treatment only in 2009 and 2012, but total N uptake was usually much less than with gypsum + N + P or NPS fertilizer treatment, suggesting the lack of N, S, and/or P in this treatment for
Table 7. Oil concentration in canola seed with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
optimum crop growth.
Compared to the control, there was a substantial reduction in total N uptake in seed + straw of canola in 2010 (also slight in 2011), when only N fertilizer was applied without any sulphate-S. Application of P along with N (NP) resulted in some increase in total N uptake in seed + straw compared to the N alone and control treatments. The combined application of N (as ammonium nitrate) + P (as triple super phosphate + S (potassium sulphate) chemical fertilizers (NPS) produced
Table 8. Total N uptake in seed + straw of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
considerably higher total N uptake in seed + straw of canola, compared to the control, in all four years. This suggests that total N uptake in seed + straw of canola can be improved significantly by using balanced NPS fertilization/ nutrition on this soil, extremely deficient in plant-available S and possibly containing insufficient amount of available P for optimum crop growth, especially for canola being a particular S-sensitive crop. Application of RRES along with N + P fertilizer usually produced total N uptake in seed + straw of canola, similar
Table 9. Total P uptake in seed + straw of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
to gypsum + N + P treatment. Total N uptake in seed + straw with both gypsum and RRES treatments were significantly greater than with the N only treatment, but only slightly less than with the NPS treatment in some years.
Application of N + S, in combination with rock phosphate and/or Penicillium bilaiae, did not produce any significant increase in total N uptake in seed + straw compared to the N + S treatment. This suggests little or no contribution of rock phosphate and/or Penicillium bilaiae
Table 10. Total K uptake in seed + straw of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
Table 11. Total S uptake in seed + straw of canola with various amendments applied annually in 2009, 2010, 2011 and 2012 at Star City, Saskatchewan.
in increasing P availability to canola. The response trends of total P, K and S uptake in seed + straw of canola to various organic and inorganic amendments were usually similar to total N uptake in seed + straw in most cases (Tables 9-11).
4. DISCUSSION
Our study investigated many alternative nutrient sources (ANS) that can be potentially used to prevent/ eliminate nutrient deficiencies in organic and/or conventional cropping systems. In our study, we included a treatment with combined application of N, P and S chemical fertilizers (NPS) to prevent all major nutrient deficiencies in soil at the experimental site in order to obtain the best yield and nutrient uptake, so that all other organic and inorganic/mineral amendments can be compared to this NPS treatment for their relative effectiveness. The NPS treatment in our study produced considerably higher seed yield, straw yield and nutrient uptake of canola compared to the no amendment control. In the following sections, we discussed results on amendments applicable to organic crop production as well as to conventional farming systems separately.
In treatments receiving only organic amendments (applicable to organic crop production), thin stillage produced the highest seed yield, straw yield and nutrient uptake in both years, and it was similar to the NPS balanced fertilization treatment. This suggests a great potential of thin stillage as an organic amendment to prevent any nutrient deficiencies and subsequently increase crop yield by increasing the availability of nutrients to crop plants. Compared to the control, fish food additive (in both years) and distiller grain dry of both wheat and corn (in 2009) produced significantly higher seed yield, straw yield and nutrient uptake. The significant increase in nutrient uptake in seed + straw with fish food additive, distiller grain dry of both wheat and distiller grain of corn compared to control also suggest the potential of these amendments in increasing the availability of nutrients and subsequently improving yield of organic crops. There was a moderate (but non-significant) increase in seed yield, straw yield and nutrient uptake from compost, alfalfa + canola meal pellets, alfalfa pellets and wood ash fine, suggesting the potential of these amendments after perhaps a long-term use. Similarly, earlier studies have shown potential yield benefits of both organic and mineral amendments and soil activators/inoculants on crop yields, produce quality and nutrient uptake [34,36,52-59]. There was a slight reduction in seed yield, straw yield and nutrient uptake from glycerol, and this was most likely due to immobilization of N and S due to wide C:N ratio in this product. Composted manure is a good supplier of N, P, K, S, and other nutrients, and is expected to increase crop yields when these nutrients are liming in soil for optimum crop growth/yield [34]. Similarly, alfalfa pellets have narrow C:N ratio in plant materials and are expected to supply N, P and other nutrients after mineralization [60]. However, in our study, composted manure and alfalfa pellets generally were not very effective in increasing crop yield and nutrient uptake, when canola was the test crop. This was probably due to low yield potential of canola at this site, especially in 2010 because of adverse weather conditions during the growing season.
In treatments where chemical fertilizers were also applied in addition to organic amendments, application of N fertilizer substantially increased seed yield, straw yield and nutrient uptake when in combination with both fine and granular wood ash treatments (especially fine wood ash), suggesting the lack of N in these treatments. Application of N in combination with glycerol also increased seed yield, straw yield and nutrient uptake, but crop yield and nutrient uptake were much less than with the gypsum + N + P treatment, as discussed in following paragraph, suggesting the lack of both N and S in glycerol.
Earlier research has suggested that gypsum can be a suitable source of S to prevent S deficiency in grass when N is also applied [61]. Sulphur deficiency in canola can also be minimized and seed yield increased by proper application of elemental S fertilizers using broadcast spread/spray applications of fine particle elemental S as a suspension (or powder) on the surface of S-deficient soils [62]. Similarly, in our present study, the use of rapid release elemental S (RRES) granular along with N + P fertilizers produced seed yield, straw yield and nutrient uptake similar to gypsum + N + P treatment, and these two treatments produced seed yield, straw yield and nutrient uptake considerably higher than the unamended control. Based on the history of this site in relation to severe S deficiency in canola in previous years and considerable reduction in canola seed yield when only N was applied without any S fertilizer in 2010 and 2011, and also in previous years [45], it is possible that spring-applied RRES has the potential to provide available S to the crop in the same growing season to the same level as gypsum or other sulphate-S sources. These results with mineral S sources suggest that gypsum and RRES can prevent S deficiency in organic crops, provided N and other nutrients are not lacking in soil.
This soil is extremely deficient in available S, and has shown severe S deficiency in canola in the growing season and considerable reduction in canola seed yield when only N was applied without any S fertilizer. Based on the history of this site in relation to severe S deficiency in canola in the growing season in previous years [45] and our present results, the reduction in seed yield with only N application was most likely due to N and S imbalance in the plants [63,64]. Our results suggest the potential of gypsum and RRES in preventing S deficiency in organic crops when grown on S-deficient soils, provided other nutrients are not limiting in soil for crop growth. Our findings also suggest that RRES has the potential to prevent S deficiency in canola by providing available S to the crop in the growing season similar to gypsum, but seed yields of canola in our experiment were relatively lower than normal for this area, especially in 2010 and 2011. The lower than normal seed yields in our study were possibly because of the choice of a juncea canola cultivar in 2009, 2010 and 2011 (with relatively lower yield potential compared to hybrid canola), plus using moderate rate of N at 80 kg·N·ha−1, and very wet and cool weather conditions in 2012. In our other adjacent experiment, comparing granular RRES and sulphate S fertilizers applied in the previous autumn and in spring at seeding using various methods of placement on the same farm (with relatively high seed yield of hybrid canola grown at 120 kg·N·ha−1), spring applied RRES increased seed yield of canola compared to the zero-S control in the first year of application but seed yield was much less than sulphate-S fertilizer. Therefore, it is possible that under high seed yield conditions, spring applied sulphate-S may be more effective in increasing seed yield of canola than spring applied RRES, when broadcast/incorporated into soil in spring. In 2012, we replaced the juncea canola cultivar with a high yielding hybrid canola to find if RRES can be as effective as sulphate-S in preventing S deficiency in canola under high seed yield conditions. As mentioned earlier, that seed yield of hybrid canola in 2012 was lower than normal for this area, and the cumulative effect of RRES after four annual applications in increasing productivity, seed yield was almost similar to the similarly-applied sulphate-S fertilizer treatment in this study.
Research has shown that crops with deep taproots can absorb nutrients from deeper soil layers [65,66]. But, if the soil profileis low in available P, then the only alternative is to add external P source [67]. For example, the use of vesicular-arbuscularmychorrhiza (VAM), Penicillium bilaiae, rock phosphate, or bone meal can increase the release of P from soil and organic P fertilizers/amendments in order to prevent P deficiency in P-deficient soils and increase crop yields [52-54,57-59,68-70]. In a field study in Saskatchewan, Takeda [68] did not find any benefit of rock phosphate application on crop yield and P uptake over two years at any of three sites, but showed increases in crop yield and P uptake at two sites from the application of rock phosphate in combination with Penicillium bilaiae. Gleddie et al. [71] also reported positive responses to Penicillium bilaiae inoculation on soils that were extremely deficient in P for optimum growth. However, in our study, there was no effect of rock phosphate and/or Penicillium bilaiae on yield and P uptake of canola in any year, at this S-deficient site with also a potential of P-deficiency [46]. It is possible that the soil at this site may not be deficient in available P to a level the may limit yield of canola because of its low yield, especially in 2010. We expected increase in crop yield and/or P uptake from the finely ground rock phosphate, because of the increase in surface area, but it did not happen. As explained earlier, this could be due to low yield potential of canola, and also possibly the released P from the fine rock phosphate fertilizer may have become again immobilized/fixed into the soil organic fraction due to greater microbial or chemical reaction of P in the finely ground rock phosphate in soil.
5. CONCLUSION
Some organic amendments showed potential for improvement in organic crop production, and in some other cases highest seed yields were obtained when both organic amendments and chemical fertilizers were applied together, or from combined application of chemical N, S and P fertilizers. These findings suggest that some organic amendments can be used to improve crop yields under organic production. These findings also suggest the potential of some inorganic amendments (e.g., rapid release elemental S and gypsum) in preventing S deficiency in organic crops, provided other nutrients are not limited in soil. The implications of these findings are that it may be possible to increase the sustainability of crop production by improving nutrient use and water use efficiency through better plant and root growth under both organic and conventional farming systems. It may also result in higher net returns to producers, improved soil quality, by returning more residues to soil, and minimize environmental damage of nitrate-N (leaching to ground water and nitrous oxide emissions), by leaving less residual nitrate-N in soils.
6. ACKNOWLEDGEMENTS
The authors thank Sulphur Solutions Inc. for financial assistance, Western Alfalfa for supplying alfalfa pellets, and D. Leach and K. Strukofffor technical assistance.