Sergio Valdivia Vega. Agronomy ABSTRACT

Transcription

1 Agronomy Sergio Valdivia Vega ABSTRACT The effect of Na on yield of sugarcane of the variety H studied in a slightly saline'soil, predominantly sodic, in the ZaAa ey on the north coast of Peru. This work was done under field conditions, in 20 plots, varying ze between 2.058m2 and 2.352m2 and with between 2 and 44% xchangeable Na. There was hardly any reduction in yield with 10% exchangeable Na. Exchangeable Na at 15% was established as the critical level which causes the yield of sugar or cane to decrease by 15%. The production of cane or sugar was reduced by half when the ESP was between 25 and 26. INTRODUCTION In the arid coast of Peru, the planting of sugarcane is spreading more and more to different types of soils previously considered non-productive: unplowed lands of coarse texture, lands without cultivation with salinity problems, or lands that previously had been used for highly tolerant crop plants, such as cotton and :'gramalote" (Parzicum purpurascens), or lands that had been used for crop plants, such as rice and sorghum which are semitolerant to salts (US Salinity Laboratory6) and to sodium (FAO- UNESC02). The yield of sugarcane in this kind of land usually decreases very considerably because sugarcane is sensitive to salts (FAO-UNESC02). The effect of salts have been well studied, and the maximum permissible level for a normal development of different crop plants has been determined. The US Salinity Laboratory6 has expressed tolerance to salts as a reduction of up to 50% in yield. On the other hand, Bernstein (in Reeve and Firemand) considers the criterion to be from 10 to 15% reduction in yield. ~here'is indeed little information on the effect of excess of exchangeable sodium on the yield of different crop plants, although some observations have been made on the effect on sugarcane. Bonnet1 observed that sugarcane grows poorly in salty lands that contain from 20.0 to 72.9% of extractable sodium. Good sugarcane growth was observed when the land contained from 4.5 to 11.4%. Fogliata and Aso3 found a negative correlation between cane yield and sodium (meq/l). Rizk and Normand5 state that it would not be economically feasible to grow sugarcane of the variety CP in Louisiana, in soils containing more than 1% sodium.

2 This work was done with the purpose of finding the required concentration of sodium in the soil to make it possible to plant sugarcane and obtain good economic yields. Taking into consideration that the sugarcane industry is highly competitive and that prices have recently decreased suddenly on the world market and in the North American market, we are obliged to obtain high yields. We consider that a yield reduction of more than 10% would make an economic profit doubtful, and that a reduction of 15% would indicate the maximum permissible level of Na in the soil. EXPERIMENTAL PROCEDURE The study was carried out on the northern coast of Peru, in field Santa Rosa, Cooperative Cayalti, Zafia Valley, where the average annual precipitation is 34mm, the average annual evaporation is 5.8 mm/day, and the average annual temperature is 22.2OC. The field was planted in September 1972 with the cane cultivar H All the plots had similar cultural treatment such as is normally used in industrial fields. The area where the 20 plots were situated was selected 13 months after the sugarcane has been planted. The area of the plots varied between m2 and mz. An attempt was made to group areas in a uniform way, with the following characteristics: a) areas where the sugarcane did not sprout, b) areas where the sugarcane grew very stunted and scarcely sprouted, c) areas with stunted growth, d),areas with vigorous growth of sugarcane, and, e) areas with lull-sized, vigorous sugarcane. After planting, 7 samples were taken from the bottom of the furrow, sites being evenly distributed in,each plot. Samples were taken at three depths: 0-30, and cm. The 7 samples from an equal depth were pooled to form one complex sample representing each plot, and samples were analyzed in the laboratory. The same procedure was used with soil samples extracted after the harvest. The exchangeable Na percentage (ESP) was determined by the method proposed by the US Salinity Laboratory6. Before the harvest, ~ W O samples of burned cane were taken from each plot. The samples were mixed and sent to the laboratory, where the % pol (P.), the % of fiber (F.) and the purity (Pu.) were determined. The field was harvested after 20 months and the total weight of each plot was obtained. From these values, the recoverable sugar yield in t/ha (Rec.Sug. t/ha) was calct~lated by the formula: Rec.Sug. (t/ha) = cane t'ha [P F f Pu. The values of cane yield (t/ha), pol % in cane, and recoverable sugar yield (t/ha) were correlated with the average exchangeable Na % of the two samplings (when plotting and after the harvest) and of the three depths (0 to 90 cm). After the hawest, 3 soil profiles, representing the whole area under study were defined and sampled. The first (plot 8) was situated in areas '

3 with very stunted growth, the second (plot 10) was situated in areas with vigorous growth and the third (plot 12) was situated in areas with fully grown, vigorous sugarcane. The r-ess~lts of the physical and chemical analyses are presented in Table 1. TABLE I. Physical and chemical properties of 3 representative profiles Characteristics Studied Plot 8 Plot 10 Plot 12 Depths Depths Depths Saturation % E Ce mmhos/cm Paste ph Exchang. Na % Soluble c 0:- meq/l Soluble HCO; meq/l Soluble C1-3 meq/l Soluble 50: - meq/l Soluble NaS meq/l Soluble Ca2+ meq/l Soluble Mgz+ meq/l Soluble KI- meq/l Ca COa % Organic matter 9% Clay % Silt % (2-50p) Water Table cm Cane yield t/ha RESULTS AND DISCUSSION Cane yield The correlation between cane yield and ESP was highly significant (r = 0.86). In Fig. 1, are shown the equation of the curve and the strong tendency for the yield to decrease as the ESP increases. It can be observed that with 45% of exchangeable NR, there is practically no production. The decrease of yield with 10% of exchangeable Na is less than 5% (St cane/ha) which indicates that from 0 to 10% of exchangeable Na has practically no deleterious effect. On the other hand, a yield decrease of cane amounting to 10 and 15% was found, when the exchangeable Na was 13 and 15 % respectively. It can be observed that at levels over 15 % of exchangeable Na, the cane yield decreases considerably. This concentration of Na caused the yield to decrease by 15% and this value is there- '*a

4 8 64 AGRONOMY fore considered to be the critical level for satisfactory development of the cane. This confirms the level found by the US Salinity Laboratory6. A severe reduction of yield (50%) was observed when the ESP was 26. FIGURE 1. Effect of sodium on cane yield in field plots. Pol % Cane EXCHANGEAB LE-SODIUM % A highly significant correlatioll was found (r = 0.85) between the pol % cane and the ESP. Similar results have been found in sugar beet by Heimann and Ratner,(in F,ogliata and Aso3). In addition, Rizk and Norrnand5 observed that, in sugarcane, the quality of juice is adversely affected by high concentration of sodium. FIGURE 2. Effect of sodium on pol % cane in field plots, ~ ~ m r ~ T r = v l - r r l r l r l i IS EXCHANGEAB LE-SODIUM '10

5 S. VALDIVIA V. 865 Fig. 2 shows the tendency of the pol % to decrease as the ESP increases. The decygase of the concentration of pol with 15% of exchangeable Na is relatively small, a high concentration of exchangeable Na (25 % ) being required to decrease the concentration of pol by 15 % (from 14.6 to 12.4). Recoverable sugar Fig. 3 shows the highly significant inverse correlation (r = 0.86) between the recoverable sugar yield and the ESP. The results are presented in relative yield % because.this gives a better basis for comparison. Soils with low sodicity (< 10 ESP) do not appreciably affect the sugar yield. A reduction of yield amounting to 10 and 15% was found with ESP of 12.5 and 15 respectively. A severe reduction ol 50% of the yield was obtained wilh 25% of exchangeable Na. A level of 15% of exchangeable Na can be considered as the critical level over which the yield is highly restricted. This confirms the value found by the US Salinity Laboratory6. FIGURE 3. Effect of sodium on recoverable sugar yield in field plots. EXCHANGEABLE-SODIUM '16 CONCLUSIONS - There were highly significant inverse correlations between the ESP and the three characteristics studied: 1) cane yield (r = 0.86), 2) pol % cane (r = OM), and 3) sugar yield (r = 0.86). - In piactice a concentration up fo 10% of exchangeable Na did not have a harmful effect on sugarcane.,

6 866 AGRONOMY - A concentration of Na in the soil of 15% can be considered as the critical level, because it decreases the production of cane or sugar by about 15 %. \ - There was practically no production with 45% exchangeable Na. - Pol % cane is more tolerant to Na than the production of cane or sugar. ACKNOWLEQGEMENT (\I The author is rnost grateful to Mr. Eladio Angulo for assistance in statistical analysing of the data. REFERENCES 1. Bonnet, J.A. (19.53). Soil salinity studies as related to sugarcane growing in South Western Puerto Rico. Proc. ISSCT, 8: FAO-UNESCO (1973). Irrigation, Drainage and Salinity. Hutchinson & Co. Ltd. London, 510 p. 3. Fogliata, F. and P. Aso. (1965). The effects of soil soluble salts on sucrose yield of sugar cane. Proc. ISSCT, 12: Reeve, R. and N. Fireman. (1967). Salt problems in relation to irrigation. Irrigation of Agricultural Lands. Amer. Soc. of Agron., Agronomy 11: Rizk, T.Y. and W.C. Normand. (1966). A field study of some effects of salinity on sugarcane. The Sugar Bulletin 44: US Salinity Laboratory. (1954). Diagnosis and Improvement of Saline and Alkali Soils. US Dep. Agr. Handbook p. EFECTO DEL EXCESO DE SOD10 EN LA PRODUCCION DE LA CANA DE AZUCAR S. Valdivia V. RESUMEN El efecto del Na en la produccion de la catia de azucar H , fue estudiado en un suelo ligeramente salino, predominantemente sodico de la costa norte del Peru (Valle de Zafia). Este trabajo se realizo bajo condiciones de campo en 20 parcelas variables entre 2058 m2 a 2352 m2 y entre 2% a 44% de Na intercambiable. Se encontro que practicamente no hay reduccion de la produccion, hasta con un 10% de Na intercambiable. Se fijo que 15% de Na intercambiable es el nivel critic0 ya que disminuye la produccion de catia o de azucar en un 15%. Ademas, el rendimiento de catia y de azucar fue reducido a la mitad cuando el ESP estuvo entre 25 a 26.