EFFECT OF HEAVY STORE DRESSING WITH ROCK PHOSPHATE ON A FINE SAND SOIL Armi Kaila University ofHelsinki, Department ofAgricultural Chemistry Received March 10, 1969 In a previous paper (Hänninen and Kaila 1960) results were reported of an attempt to study the possibilities of improving the soil phosphorus status by a store dressing with rock phosphate to such a degree that an annual application of superphosphate would no more be profitable. It was found in two field trials that 1000 kg/ha of rock phosphate was not enough to produce the effect wanted, and that even higher amounts than 2000 kg/ha may be recommendable under Finnish conditions. Therefore, a new field trial was started in 1960 by the late Dr. Pentti Hänninen, then the head of the agricultural experiment station in Central Finland, with applications of rock phosphate in quantities from 4000 to 12000 kg/ha. This trial has been continued for nine years. Part of the results are reported in the present paper. The primary yield results and the samples were provided in the first four experimental years by Dr. Hänninen, in 1968 by the present head of the experiment station, Mr Paavo Simojoki. The analytical work has been performed by the author. Field trial In the spring 1960 the following amounts of finely ground North African rock phosphate (Hyper- phosphate) were applied to a fine sand soil; 1. No phosphate 2. Rock phosphate 4000 kg/ha 3. » » 8000 » 4. » » 12000 » Using the split plot technique, an annual dressing with 200 kg/ha ofsuperphosphatewas applied from 1961 to 1967. Basal dressings with nitrogen as ammonium nitrate limestone and with potassium as potassium chloride were used. The test crop was barley in the first year, as a nurse crop of the red clover-timothy ley which grew for six years. In the last two years barley was grown. https://www.c-info.fi/en/info/?token=AMO7yXiDrnilBJ7E.ZO6qJYhCRMIx4RUJzmo2ew.QIjx8V3B6giPLILg3caM0P6oUe0fUkh89E3lamPvhm5aNYhLxVPGknxp9LMZlfBDgjF9IXiG0AsahGemIq9eUXeCwfX-8tpEfRESzDzbgohoERn3C3LSV8cnWO_BXIl6JRm9ylpt7_EWd7oshcRxooeI_QOclrXr For the main treatments, the plots harvested were 25 m 2, the area of subplots harvested was 14 m 2. Both the main treatments and the subtreatments within a block were randomized, and the whole experi- ment consisted of four blocks. According to the manufacturer’s analysis, the rock phosphate used contained 12.6 % P. The P content of superphosphate was on average 8.5 %. The rock phosphate was carefully worked in with plough and spade harrow. Superphosphate was applied as surface dressing to the ley. Soil samples were collected in June 1960, or about four weeks after rock phosphate was applied, from successive layers of 2.5 cm down to the depth of 15 cm of all plots, and analysed separately. In 1968 soil samples were taken from the plough layer ofall remaining 27 subplots: 5 subplots were at that timerejected because of disturbance caused by ditching. Plant samples were collected at harvest from all plots or subplots in 1960—1963 and analysed sepa- rately. In 1968 grain samples were provided from all 27 remaining subplots, but only combined straw samples from the 8 subtreatments were available. Analytical methods Inorganic phosphorus in soil samples was fractionated by a somewhat modified method of Chang and Jackson (1957). Readily soluble phosphorus was estimated by extracting with 0.01 M CaCl2 for 18 hours in the ratio ofsoil to solution of 1 to 5. Also the Bray 1 test and an acetic acid test were used. Soil pH was measured in a 1 to 2.5 suspension in 0.01 M CaCl2 . Total phosphorus in plant samples was determined from ash solutions with the ammonium vanadate- molybdate method, total calcium and magnesium with versenate titration in 1960—1963, and with a Perkin Elmer Atomic absorption spectrophotometer 290 in 1968, and potassium with an EEL flame photometer. Total nitrogen was determined with the common Kjeldahl digestion. The results were treated with Duncan’s new multiple range test (Duncan 1955). Values marked by the same letter in the tables do not differ at the 5 per cent level. Results Years 1960 196 3. The pH-values in Table 1 show that the calcium carbonate in rock phosphate has significantly decreased the acidity in all layers, most at the depth from 2.5 to 15 cm. The soil was not well buffered, since it was rather coarse textured and had a low humus content (2.1 % organic carbon). In the previous trials (Hänninen and Kaila 1960) rock phosphate was worked in only by spade harrow, and the soil analyses indicated that a large part of the fertilizer remained in the top layer of 0 to 7.5 cm. The more effective mixing with both plough Table 1. pH in soil samples four weeks after the application ofrock phosphate. Depth Rock phosphate kg/ha cm 0 4000 8000 12000 0 2.5 4.8* 4.9C 4.9C 5.0* 2.5 5 4.7° 4.8* 4.9 C 5.1/ 5 7.5 4.7" 4.9C 5.0' 5.1/ 7.5—10 4.8* 4.9* 5.0* 5.2* 10 —12.5 4.7" 4.9" 4.9* 5.2* 12.5—15 4.7a 4.8* 5.C 5.1/ 134 135 and harrow in the present trial distributed the fertilizer fairly well at least until the depth of 15 cm, as may be seen from Table 2. Table 2. Fluoride-soluble and acid-soluble P fractions in soil samples four weeks after the application of 0, 4000, 8000, or 12000 kg/ha of rock phosphate. Inorganic P ppm extracted by Depth NH4F H 2 S04 cm 0 4000 8000 12000 0 4000 8000 12000 0 2.5 33" 53abc 60"6c 66bc 43o* 540* 740/* 2.5 5 33" 59" tc 59,ie 656c 4Bo* 610/ 880** 5 7.5 35"4 62"6c 69' 80* 310* 600/ 800/* 1160*' 7.5—10 35ab 6\abc 62 » » 8000 » » » 12000 » 2.91* 2.86* 1.26» 1.17*' 2.94* 2.89* 1.33 V 1.36 The surface dressing with superphosphate has distinctly increased the nitrogen content of clover and grasses, when the store dressing with rock phosphate was 0 or 4000 kg/ha. 139 This may not be attributed only to the effect of sulphur in superphosphate, but it is likely to be due to a better phosphate nutrition, since also the higher applications of rock phosphate alone have produced equal increases in the nitrogen content of theplant samples. Year 196 8. The soil samples collected at the end of the experimental period in 1968 did not show any accumulation of superphosphate phosphorus, although the total amount applied in seven years was not insignificant, coming up to about 120 kg/ha of P. The effect of the store dressing with rock phosphate on the soil phosphorus analyses was also less marked than could be expected. It is likely that the ploughing of the soil after the last ley crop was harvested brought the surface layers with their fertilizer phosphorus to a deeper level than the sampling depth in 1968. Table 6. Phosphorus fractions in the soil samples in 1968. Rock Inorganic P ppm extracted by phosphate NH,F XaOll H2 S04 in 1960 ■ 0 Super 0 Super 0 Super 0 36" 42"4 163/ 158/ 311* 297* 4000 6ibc 80crf 148/ 162/ 407** 397** 8000 95* 8icd' 166/ 169/ 636'>' 541*' 12000 95 A 99' 157/ 158/ 694'>' 758> The results of the phosphorus fractionation of these samples are recorded in Table 6. No effect offertilizers is found in the alkali-soluble fraction, representing iron bound phos- phorus. The fluoride-soluble fraction supposed to be aluminium bound phosphorus or some lower calcium phosphates, is the higher the heavier the store dressing was, but the annual superphosphate applications have not significantly increased these values. The large variation hampers comparing of the results, particularly those of the acid-soluble or apatite-like phosphorus. Yet, the largest part of the rock phosphate recovered by these analyses appears to exist in the more or less unchanged apatite. The results of the phosphorus tests are in accordance with the fractionation data. There was no indication of any effect of superphosphate either on the phosphorus con- tent of the grain or on that ofstraw of the cereal in 1968. The phosphorus content of grains was 3.86 % without phosphorus fertilizers, and it increased with increasing amounts of rock phosphate up to 4.00 % on the plots with the heaviest dressing. Because of the large variation, this difference is not statistically significant. The straw samples contained from 1.01 to 1.33 % P quite independent of the amount of fertilizers applied during the experi- mental period. No differences were found in the nitrogen, calcium, magnesium, or potassium contents of these plant samples. Discussion In this acid fine sand soil crops responded to the heavy store dressing with rock phos- phate, at least in the first four experimental years. From the second to the fourth year, the dry matter yield ofred clover-timothy ley from the rock phosphate plots was not increased 140 by the annual surface dressing with superphosphate. Superphosphate tended, however, to increase the phosphorus content of hay, though only in a few cases this increase was statistically significant. The lowest amount of rock phosphate, 4000 kg/ha, was effective enough to produce higher dry matter yields than the annual superphosphate application alone, and the phos- phorus content of hay was equal in both cases. The heavier store dressings, 8000 or 12000 kg/ha rock of phosphate, did no more increase the dry matter yields, but the phosphorus content of hay produced by them tended to be higher than that from the plots with 4000 kg/ha of rock phosphate. It is of interest to note that the apparent recovery of rock phosphate phosphorus re- mained at the same levels in the first four experimental years, or it was, on an average, 2.6 kg/year from 4000 kg, 3.7 kg/year from 8000 kg, and 4.6 kg/year from 12000 kg. The application of superphosphate decreased these recoveries, but only slightly. The apparent recovery of superphosphate phosphorus when no rock phosphate was used was 1.5 to 1.9 kg/ha, or only about ten per cent in these three years. The relatively efficient working down of rock phosphate was likely to improve its utilization and its reaction with the soil. In the first year samples the rock phosphate phos- phorus was almost completely recovered by the fluoride and acid extractions of the fractio- nation procedure. In the samples collected at the end of the trial, the recovery was much poorer. This may be partly attributed to the large variation of the soil in the experimental area, and partly to the possibility that the surface layers with their fertilizer phosphorus were brought by ploughing down to a deeper level than the sampling depth in 1968. The latter possibility may be responsible also to the fact that no sign of the application of superphosphate during seven years could be detected by the soil analyses in 1968. This fine sand soil seems to represent one of the extreme types of phosphate retention, or the soils which sorb applied soluble phosphorus almost completely by aluminium oxides and hydroxides, or as forms extractable by ammonium fluoride of the fractionation pro- cedure (Kaila 1965). At least, no effect offertilizers was found in the alkali-soluble fraction, supposed to be iron bound phosphorus and of a markedly lower availability than the fluoride-soluble phosphorus. Soils containing large amounts of active iron oxides and hydroxides are likely to sorb the slowly dissolving rock phosphate phosphorus so effectively that the response of crops to rock phosphate dressing may not be marked. In this soil 4000 kg/ha ofrock phosphate seemed to be enough to improve the phosphorus conditions to such degree that the annual applications of superphosphate were no more profitable. In a soil of the opposite retention type, e.g. in a Litorina soil rich in iron, far larger amounts of rock phosphate may be needed. It is likely that even in soils in which the sorbed phosphate is more equally distributed between the aluminium and iron bound forms, very heavy applications of rock phosphate will not be the most profitable way to the improvement of their phosphorus conditions. Summary Results are reported of a long-term field trial on acid fine sand soil in which the effects of store dressing with rock phosphate in amounts of 0, 4000, 8000, or 12000 kg/ha was 141 studied comparing them with an annual application of 200 kg/ha of superphosphate using the split plot technique. In the first four years, more thoroughly studied, the response to the store dressing with rock phosphate was distinct both in the dry matter yields and the phosphorus content of the cereal and the red clover-timothy hay. The differences between the various rates of rock phosphate treatments were not statistically significant, though there was some tend- ency to higher results with larger amounts of rock phosphate. The annual applications ofsuperphosphate as surface dressing to the ley did not brought about any significant increase in the dry matter yield of the rock phosphate plots, and although they tended to increase the phosphorus content of hay, the increase was statistic- ally significant only in a few cases. No effect was found on the phosphorus content ofbarley grain and straw in the ninth experimental year. No differenceswere found in the calcium, magnesium, or potassium content of the plant samples from the variously treated plots. Nitrogen content of clover and timothy was increased by both rock phosphate and superphosphate, particularly in the first year ley. In this soil, 4000 kg/ha of rock phosphate was effective enough to produce higher dry matter yields of hay, with equal phosphorus content, than the annual application of 200 kg/ha of superphosphate. Soil analyses indicated that this soil represented the extreme pattern of phosphorus retention in which applied phosphate is almost completely retained as aluminium bound forms of the fluoride soluble fraction supposed to be fairly available. 11 was suggested that in soils which retain the slowly dissolving rock phosphate phosphorus mainly as less available iron bound forms, heavy applications of rock phosphate will not be a profitable way to improve the phosphorus conditions. REFERENCES Chang, S. C. & Jackson, M. L. 1957. Fractionation of soil phosphorus. Soil Sci. 84: 133—144. Duncan, D. B. 1955: Multiple range and multiple F tests. Biometrics 11: 1—42. Hänninen, P. & Kaila, A. 1960. Field trials on the store dressing with rock phosphate. J. Sci. Agric. Soc. Finland 32: 107—117. Kaila, A. 1965. The fate of water-soluble phosphate applied to some mineral soils. Ibid. 37: 104—115. —»—- 1969. Residual effect of rock phosphate and superphosphate. Ibid. 41: 82—88. —»—- & Hänninen, P. 1960. Response of ley plants to rock phosphate and superphosphate. Ibid. 32: 52—61. SELOSTUS VOIMAKKAAN HIENOFOSFAATTI-PERUSLANNOITUKSEN VAIKUTUKSESTA HIETAMAASSA Armi Kaila Tliopiston maanviljelyskemian laitos, Viikki Tutkimuksessa on esitetty osa Keski-Suomen koeaseman edesmenneen johtajan tohtori Pentti Hänni- sen kanssa aloitetusta kenttäkokeesta, jossa yritettiin selvittää, voidaanko antamalla hyvin suuria hieno- fosfaattimääriä varastolannoituksena parantaa maan fosforitilaa niin paljon, että vuotuinen superfosfaatti- 142 lannoitus käy tarpeettomaksi. Hienofosfaattia annettiin v. 1960 huolellisesti maahan muokattuna 0, 4000, 8000 tai 12000 kg/ha ja seuraavasta vuodesta alkaen osaruutumenetelmää käyttäen 200 kg/ha superfosfaattia pintalannoituksena apila-timoteinurmelle. Todettiin, että neljän ensimmäisen koevuoden aikana ohra ja nurmi antoivat pienimmällä hienofos- faatin määrällä selvän sadonlisäyksen, joka ei merkitsevästi eronnut suuremmilla määrillä saaduista, joskin kasviaineksen fosforipitoisuus näytti lisääntyvän lannoitemäärän mukana. Superfosfaatti ei lisännyt hieno- fosfaattia saaneiden ruutujen sadon määrää eikä merkitsevästi sen fosforipitoisuuttakaan. 4000 kg/ha hienofosfaattia riitti ainakin saman tuloksen saavuttamiseen kuin vuotuinen pelkkä superfosfaattilannoitus tässä happamassa hietamaassa, jossa maa-analyysien mukaan voitiin todeta hienofosfaatista liuenneen fosforin pidättyneen yksinomaan fluoridiin uuttuvaan fraktioon, siis verraten käyttökelpoiseen muotoon. Tosin suurin osa hienofosfaatin fosforista näytti vielä kokeen lopussa eli 9 vuoden kuluttua olevan melko muuttumattomana apatiittina happoon liukenevassa fraktiossa. Ilmeisesti maissa, joissa hienofosfaatista hitaasti liukeneva fosfori pidättyy vaikeasti käytettävissä ole- viksi raudan komplekseiksi, hienofosfaatin teho jää heikommaksi kuin tässä maassa.