Phosphate rock (PR) was applied to one conventional and two organic dairy fields and planted with buckwheat (Fagopyrum esculentum) as a green manure crop. In total, five types of PR were applied at three application rates in order to determine the yield, concentration of P in the aboveground tissue and the P uptake of buckwheat. It was found that PR of relatively high carbonate substitution and small particle diameter could increase buckwheat tissue concentrations to a quality such that mineralization of the buckwheat mulch could occur. Buckwheat mulch and residual PR increased soil P flux as determined by anion exchange membranes in situ in the following spring. This provides evidence that buckwheat of high P quality has the potential to supply P to a subsequent crop

Arcand, M M

Lynch, D H

van Straaten, P

Voroney, R P

English

Organic Eprints

Aspects of Applied Biology 79, 2006What will organic farming deliver? COR 2006283Improving green manure quality with phosphate rocks in Ontario CanadaBy M M ARCAND1, D H LYNCH2, R P VORONEY1 & P VAN STRAATEN11University of Guelph, Guelph, ON, N1G 2W1, Canada2Nova Scotia Agricultural College, Truro, NS, B2N 5E3, CanadaSummaryPhosphate rock (PR) was applied to one conventional and two organic dairy ﬁ  elds and planted with buckwheat (Fagopyrum esculentum) as a green manure crop.  In total, ﬁ  ve types of PR were applied at three application rates in order to determine the yield, concentration of P in the aboveground tissue and the P uptake of buckwheat. It was found that PR of relatively high carbonate substitution and small particle diameter could increase buckwheat tissue concentrations to a quality such that mineralization of the buckwheat mulch could occur.  Buckwheat mulch and residual PR increased soil P ﬂ  ux as determined by anion exchange membranes in situ in the following spring. This provides evidence that buckwheat of high P quality has the potential to supply P to a subsequent crop.  Keywords: Phosphate rock, Fagopyrum esculentum, green manure, soil phosphorusIntroductionAgricultural soils under long-term organic management can become deﬁ  cient in plant-available phosphorus (P) over time (Entz et al., 2001). P fertilisation on organic farms depends primarily on the on-farm recycling of organic materials, such as compost, green manures (GM), mulches and farmyard manures with minimal farm P inputs (Loes & Ogaard, 2001). In an attempt to avoid P deﬁ  ciencies in growing crops, application of phosphate rock (PR) has been proposed; however evidence of their effectiveness in calcareous soils is required before PR use can be widely recommended in Canada. Certain plant species exhibit mechanisms localized in the rhizosphere that allow for the efﬁ  cient use of P through the dissolution of PR. Buckwheat (Fagopyrum esculentum), a common cover crop in organic agriculture, has been shown to utilize P from PR even in calcareous soils (Zhu et al., 2002). Additionally, it has been found that the P concentration of buckwheat tissue can reach luxury levels (beyond 0.5% P) (Bekele et al., 1983). When grown as a green manure crop, buckwheat has the potential for supplying P to subsequent crops if the concentration of P in the tissue is high enough for mineralization to occur or to decrease P adsorption (Nziguheba et al., 1998). This ﬁ  eld study had two primary objectives: to evaluate the effects of ﬁ  ve PR of varying mineralogy and origin on yield and aboveground tissue P of a buckwheat crop; and to determine if mulching and incorporating the residues from buckwheat grown with PR inﬂ  uenced soil P availability the following spring.284Materials and MethodsPhosphate rock characterization and ﬁ  eld applicationThe experiment was conducted on one conventional (CON) and two organic (ORG1 and ORG2) dairy farms in Southwestern Ontario, Canada. The ﬁ  eld sites were on loam soils of the Podzol order and annual rainfall was 960 mm. In order to maximize the potential for PR treatment effects on plant growth, ﬁ  elds were selected based on low to medium (< 10.0 ppm P) available P (NaHCO3-extractable) levels. Soil pH was 7.5, 7.6 and 6.9 for ORG1, ORG2, and CON, respectively.   Additionally, ﬁ  elds previously cropped in alfalfa were chosen to ensure an adequate supply of N for the buckwheat crop. The PRs used in the experiment vary in geological and geographical origin and as a result will vary chemically and mineralogically. Table 1 highlights PR characteristics relevant to solubility and plant uptake. PR solubility increases with decreased particle size and length of the unit-cell a-axis, which indicates an increase in carbonate substitution of the apatite mineral.Table 1. Selected characteristics of the phosphate rocks PR Deposit location Total P Available P a-axis Particle size(%) (mg P kg rock-1) (Å) (% passing 0.125 mm)SRPR Ontario, Can.   1.4 0 no data no dataVPR Ontario, Can. 16.8 80 9.3712   8.3CPR Florida, USA   8.7 100 9.3520 93.0TPR Tennessee, USA 12.7 118 9.3396 10.3PPR N. Carolina, USA 10.1 24 9.3234   1.1At each site, the experiment was arranged as a two factor (P treatment and P application rate) randomized complete block design with four replicates. Three PR were applied on the organic ﬁ  eld sites, while ﬁ  ve PR and two soluble fertilizers (MAP and TSP) were applied on the conventional ﬁ  eld site for comparison. All of the P treatments were applied on ploughed soils at rates of 100, 400 and 800 kg total P ha-1 in June 2004 and immediately incorporated by rototilling to 10 cm. A control treatment with no addition of P was included. Buckwheat planting, harvesting and mulchingBuckwheat was sown at 67 kg ha-1, with no additional tillage, within one week following the incorporation of the P fertility treatments. Buckwheat biomass yield was determined at approximately seven weeks of growth (just prior to seed set) by cutting a 1.10 m × 5 m swath. The fresh biomass weight was taken in the ﬁ  eld and a subsample (1 kg) was retained, dried (60°C for 48 h) and ground (< 1 mm). The tissue P as a percentage of total plant biomass was determined by high temperature dry oxidation of the organic matter and dissolution of the ash with 1 M HCl. Total P in the digests was determined using atomic absorption. At the time of buckwheat harvest in August, all the aboveground buckwheat material (2.7 to 3.0 t DM ha-1) from each plot was returned to half of the plot (subplot). This gave subtreatments of unmulched and double rate mulching. The buckwheat mulch remained on the soil surface over the winter and was rototilled in spring of 2005. An annual ryegrass (Lolium multiﬂ  orum) crop was planted after rototilling with no additional tillage; however the ryegrass yield and nutrient data will not be presented here.   Soil sampling and analysisIn spring 2005, the ﬂ  ux of soil P (µg 10 cm-2) was determined using anion exchange membranes encased in plastic PRSTM probes (Plant Root SimulatorsTM, Western Ag Innovations, Saskatoon, SK, Canada). Three probes per subplot were inserted in the soil (0-10 cm depth) prior to tillage, 285removed and immediately replaced following rototilling of the buckwheat mulch. For time management reasons, only organic plots applied with CPR at the 400 and 800 kg P ha-1 rate and VPR at the 800 kg P ha-1 rate were analysed as well as the control plots. The ﬂ  ux of P was also monitored on the control and TSP (800 kg P ha-1 rate) main plots on the conventional site.  The probes were removed and replaced with clean probes every two weeks for a total of 8 weeks. The P accumulated in the probes was eluted with 0.5 M HCl and analysed using the Murphy-Riley method. Tukey-Kramer multiple comparisons test was used to determine differences (P < 0.05) between treatment means.ResultsConcentration of P in buckwheat tissue and P uptake due to PR applicationP fertility treatments signiﬁ  cantly affected buckwheat biomass yield on the conventional site only.  Mean yields for each farm site were 3.13, 2.79, and 2.81 t DM ha-1 for ORG1, ORG2, and CON, respectively. Fig. 1 highlights the response of the P concentration in buckwheat to P treatment and rates. VPR and the SRPR were ineffective at increasing buckwheat tissue P concentrations compared to the control on any of the farm sites. CPR improved the concentration of P in buckwheat tissue by as much as 103% on the ORG2 site compared to the control. Application rate did not signiﬁ  cantly affect yield on this site (data not shown).  ORG2 had the lowest initial available P (4.8 mg P kg soil-1), and it was expected that the response to P addition would be the most pronounced. The effectiveness of CPR was consistent across both organic farms. On the CON ﬁ  eld site, TPR and PPR at 800 kg P ha-1 produced similar gains in tissue P concentration as TSP and MAP at 100 and 400 kg P ha-1. The maximum concentration of P in the buckwheat tissue attained by any PR was 0.399% with application of 800 kg P ha-1 of CPR on the CON site. Among organic sites, the same treatment (CPR800) also produced the highest buckwheat tissue concentration, 0.347% on Fig 1. The concentration of P % in the aboveground buckwheat tissue for CON and ORG1 sites. Bars indicate standard errors (n=4 df=18).0.10.20.30.40.50.60.70.80 200 400 600 800 1000P application rate (kg P ha-1)BuckwheattissueP(%)CPR VPR SRPR PPRTPR TSP MAPCON0.10.20.30.40 200 400 600 800 1000P application rate (kg P ha-1)BuckwheattissueP(%)ORG1286site ORG1.  Effect of buckwheat mulch and residual PR on spring soil P ﬂ  uxIn spring 2005, cumulative soil P ﬂ  ux (µg P 10 cm-2), on mulched subplots for treatments CPR and TSP applied at 800 kg P ha-1 was signiﬁ  cantly greater (8.5 and 95.2, respectively) than the control (5.21 µg P 10 cm-2) over 8 weeks. The initial two weeks in May resulted in the largest ﬂ  ush of P (2.02 µg 10 cm-2), likely due to drought conditions in late May and early June which would limit P movement. Both rates of CPR application produced P ﬂ  uxes greater than the control in the ﬁ  rst two weeks of measurement in early May 2005 (Fig. 2). There were no signiﬁ  cant differences in P ﬂ  ux due to PR in subsequent dates apart from CPR at the highest rate in the ﬁ  nal two weeks (end of June 2005). There was no mulching and PR interaction; however mulching increased the average two week soil P ﬂ  ux over unmulched plots by 38%.  Available P in the soils was signiﬁ  cantly increased due to buckwheat mulching in April and June. CPR applied at 800 kg P ha-1 increased available P of soils sampled in June by 36% (data not shown).  Fig. 2. Soil P ﬂ  ux (µg P 10cm-2) over each two week period on site ORG 1 as sampled by PRSTM probes. There was a signiﬁ  cant sampling date, P treatment, and application rate interaction. Similar letters indicate no signiﬁ  cant difference between treatment means by Tukey-Kramer. Bars indicate standard errors (n=8 df=87). The arrow indicates the two week period where rototilling and ryegrass planting occurred.  DiscussionBuckwheat utilised P from CPR even in soils with high pH, suggesting that the limiting factor for the use of the PR is not necessarily due to soil or crop factors, but due to the characteristics of the rock. The very large grain size limits the use of PPR and TPR in supplying P to plants despite the high degree of carbonate substitution in these rocks. Grinding can improve the agronomic effectiveness of PR; however the cost to grind the material and the lack of appropriate machinery to spread such ﬁ  ne material would limit its adoption (Bolland & Gilkes, 1989). Buckwheat was able to utilize CPR most effectively due to the combination of the small grain size and relatively 0.000.501.001.502.002.503.003.504.00ControlVPR800CPR400CPR800ControlVPR800CPR400CPR800ControlVPR800CPR400CPR800ControlVPR800CPR400CPR800Week 1 to 2 Week 5 to 6 Week 7 to 8 Week 9 to10PR treatmentand application rate (kg P ha-1) andsampling periodsPflux(ìgP10cm-22weeks-1) ecda a a a a a ab ab abcabcdabcdbcdcd cd287high carbonate substitution of the apatite mineral in the PR. Additionally, the large volume of all PR applied to the soil likely increased PR contact with the buckwheat roots, increasing the likelihood of dissolution by H+ released by the plant.  The high P concentration of buckwheat tissue resulted in increased ﬂ  ux of P in soil of plots receiving CPR at the highest rate of application in the year following initial application. The concentration of P in the buckwheat was 0.35%, which is above the concentration that Nziguheba et al. (1998) found was necessary to decrease P adsorption in high P sorbing soils. In the present study, the initial concentration of P in the buckwheat residue explained 74% of the variation in cumulative soil P ﬂ  ux, while the total amount of P applied in the buckwheat residue could only explain 39% of the variation. Pypers et al. (2005) also found that when plant residues of varying P contents were added to soil at 45 kg P ha-1, the P concentration of the residue had more effect on P availability than the total amount of P added to the soil in the residue. Thus the quality rather than the quantity of the residue determines the availability of P from these organic materials.  Based on the present soil P ﬂ  ux data, buckwheat grown with CPR at high rates of application has the potential for supplying P to a subsequent crop. Further study is currently being conducted on the response of annual ryegrass to buckwheat mulching and residual PR.   AcknowledgementsThe authors wish to acknowledge the Natural Science and Engineering Research Council of Canada, the Ontario Ministry of Agriculture and Food, the Canada Research Chairs Programme and the Organic Agriculture Centre of Canada for ﬁ  nancial assistance. The authors also extend appreciation to the farmers for their participation in the study.ReferencesBekele T, Cino B J, Ehlert P A I, van Der Maas A A, van Diest A. 1983. An evaluation of plant-borne factors promoting the solubilization of alkaline rock phosphates. Plant and Soil 75: 361–378.Bolland M D A, Gilkes R J. 1989. Reactive rock phosphate fertilizers and soil testing for phosphorus: the effect of particle size of the rock phosphate. Fertilizer Research 21:75–93.Entz  M H, Guilford R,  Gulden R. 2001. Crop yield and soil nutrient status on 14 organic farms in the eastern portion of the northern great plains. Canadian Journal of Plant Science 81:351–354. Loes A-K, Ogaard A F. 2001. Long-term changes in extractable soil phosphorus (P) in organic dairy farming systems. Plant and Soil 237:321–332. Nziguheba G, Palm C A, Buresh R J, Smithson, P C. 1998. Soil phosphorus fractions and adsorption as affected by organic and inorganic sources. Plant and Soil 198:159–168. Pypers P, Verstraete S, Thi C P, Merckx R. 2005. Changes in mineral nitrogen, phosphorus availability and salt-extractable aluminium following the application of green manure residues in two weathered soils of South Vietnam. Soil Biology and Biochemistry 37:163–172.Zhu Y-, He Y-, Smith S E,  Smith F A. 2002. Buckwheat (Fagopyrum esculentum Moench) has high capacity to take up phosphorus (P) from a calcium (Ca)-bound source. Plant and Soil 239:1–8. 

Improving green manure quality with phosphate rocks in Ontario Canada

Abstract

Similar works

Full text

Available Versions

Organic Eprints