Agronomy SUGARCANE PRODUCTION IN FUNCTION OF THE RAINFALL AND NITROGEN APPLICATION. Franco A. Fogliata and Carlos A. Gargiulo

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1 Agronomy C SUGARCANE PRODUCTON N FUNCTON OF THE RANFALL AND NTROGEN APPLCATON Franco A. Fogliata and Carlos A. Gargiulo Agricultural Experiment Station, Tucumhn, Argentine Rep. ABSTRACT n the Tucuman province, Argentine, the sugarcane crop is characterized because it is principally developed in areas without irrigation and the nitrogen is the main fertilizer used. With the aim of establishing the actual terms of the interaction rainfall x nitrogen in function of the sugarcane yield, the best combinations have been determined between those parameters to the two principal varieties of sugarcane grown. NTRODUCTON The results of previous experiencies permitted to obtain from the variety CP variations of production according to the rainfalls and the nitrogened fertilization. The present work gives more details about that information to the varieties NA and NA that occupies between the 60-70% bf the sugarcane area of the Tucuman province. This work is motivated by the fact that in Tucumin the sugarcane grows principally in fields without irrigation and the nitrogen is the main nutrient used, because there has not been found significant responses to P and K, except in small areas. That is why it is necessary to know the terms in which the interaction rainfall x nitrogen is developed to both varieties. MATERALS AND METHODS Data from 8 tests on fertilization of the, type NPK 33 has been used during 1969 to 1973 but in this study were only used the information obtained with the application of nitrogen because of the reason pointed out before. The values of tn/ha from cane and sugar to the doses of 0, 60 and 120 kg/ha of N were statistically related with the rainfall of the agricultural year to the varieties analyzed. To the calculations of the values that represent the interaction rainfall x nitrogen, two mathematical functions were employed. One of them gave as a result the following lorm~la:~ Y=a$'b~'+cL+dN2+ el2$fln "'

2 1418 AGRONOMY were Y = sugar or cane production per ha N = nitrogen doses L = rainfall a,b,c,d,e,f = regression coefficient to be estimated. To the parabola that show the variation according to the rainfall and the N applied were employed cuadratics equation of the following type: RESULTS AND DSCUSSON From the obtained results which corresponds to a test in soils of the argiudol and hapludol type (with different phase), representatives values have been selected to avoid an excess of information. Because of that as a variety only NA is considered and because it is the variety more cultivated in TucumGn. The climate of the zone according to Koppen classification corresponds to "Cwa" (temperate-warm-wet with warm summer and dry winter) and is characteristic of the subtropical Tucum6n area. The following Tables and 1 show the expected value of cane and sugar production per ha for the variety NA 56-79, beginning with determined doses of nitrogen and with different quantities of rainfalls. Tables 11 and V show the group of the two varieties NA and NA in one locality (trial in the Experiment Station). The best conditions of yield caused that the value obtained from cane per ha were higher that those from general average as variety. The coefficients of determination (R2) were 0,77 to the cane/ha and of 0,80 for the sugar/ha. This shows that the action of nitrogen and rainfalls together represent to the production of cane the 77% and for the sugar the 80%. TABLE. Relation between rainfalls, nitrogen applied and yield of cane tn/ha in NA Rainfall (mm) 0 20 NTROGEN (kg/ha) Y = 108,l f 0,111 N - 0,143 L - 0,00134 N2 + 0, L2 + 0, NL.

3 F.A. FiOGLATA AND C.A. GARGULO 1419 TABLE. Relation between rainfalls, nitrogen applied and yield of sugar tn/ha in NA NTROGEN (kg/ha) Rainfall (mm) Y = 19,36 f 0,0211 N - 0,0327 L - 0, N2 + 0, L2-0, LN. TABLE. Relation between rainfalls, nitrogen and yield of cane tn/ha in the Experiment Station trial. NTROGEN (kg/ha) Rainfall (mm) Y = - 87,5 + 0,0432 N + 0,286 L - 0, N2-0, L2 + 0, LN. TABLE V. Relation between rainfalls, nitrogen applied and yield of sugar tn/ha in the Experiment Station trial. NTROGEN (kg/ha) Rainfall (mm)

4 1420 AGRONOMY n all the cases it is observed that without exception, the increment of rainfalls cmtributes to a better utilization of the nitrosned fertilizer. Generally the yield reached a maximum and later on there is a tendency to decrease. TABLE V. Better interaction between rainfall and nitrogen fertilizer. Varieties and Locality Rainfall mm N kg/ha Yield tn/ha NA (cane) ,5-94,6 " (sugar), ,60 1 ', NA (cane) ,9 " (sugar) ,52-8,53 CP (cane)* " " (sugar) Experiment Sta. (cane) ,6 ' (sugar) ,57 * From Fogliata and Dip(2). n Table V the best yields obtained have been summarized according to the found interaction. Although the outstanding coinbinations of rainfall x nitrogen are there, it is important to note that as the addition of nitrogen is controlable the rainfall is not. That is why it is important to know for the diflerent possible rainfalls of an "agricultural year" which are the minimal doses that produce a highest yield of cane by ha. This is showed in Table V. As an additional information the values obtained by Fogliata and Dip2 with the variety CP have been included in this table. The variations of yield in tn cane/ha to each rate of nitrogen according to the rainfalls with the varieties NA and CP were represented graphically in Figures 1 and 2. t can be seen that with low rainfalls, the tonnage obtained is lower than when there is a higher volume of water to the same dosage of fertilizer. For NA here we can observe that to the averages of all the plots during four years of harvest, when it rained 834 mm during the "agricultural year" there was a better yield than with mm. That was caused because during that year, that miner quantity of water was better distributed during the critical months of water requirements for sugarcane compared with the year that rained mm. This agrees with previous experiences in the sense that the rainfalls that present a better association with the yield are those from December to February, (Fogliata and Dip2).

5 F.A. POGLATA AND C.A. GARGULO 1421 TABLE V. Minimal doses of N that produce maximum yields under differents rainfalls. Varieties and Localities Kg N/ha Rainfall (mm) NA (cane) " (cane) CP (cane) Experiment Sta. (cane) For NA only, the parabolas that represent to each dose point out the differences between the treatment respect to the check plot (0 kg N/ha) and the behaviour between them is the dose of 60 and 120 kg N/ha. The only fact of increasing the production on the three treatments with the increasing of rainfalls indicates that there is a bigger dependence of the yielding per ha to the effects of the rainfall inore than that of the nitrogen fertilization. FGURE 1. Association between rainfall, nitrogen and yield of tn cane/ha for NA

6 1422 AGRONOMY FGURE 2. Association between rainfall, nitrogen and yield of tn cane/ha for CP ROO Rainfall (mm). FGURE 3. Kg sugar by ha in function of the rainfall for each dose of nitrogen. Variety NA Rainfall (mm)

7 F.A. FOGLATA AND C.A. GARGULO 1423 FGURE 4. Tn cane by ha in function of the rainfall for each dose of nitrogen. Variety NA Tn cane/hs t 117,894 /,cn 113,953 = Z0 kg 1270 Rainfall (mm> The work reveals the close association that there exists between the interaction rainfall x nitrogen, being the most dominant the rainfall factors. This is shown because to a same dose of nitrogen result different yields of cane and sugar per ha according to the rainfall. With the variety studied an average to the four years of best yield of'103 tn cane/ha and 12,60 tn sugar/ha and with quantities of rainfalls that are near to the requirements of water of the sugarcane. These values are fairly good if it is considered the scarce ten months of the cycle between sprouting and harvesting. These values are from a dose of 100 kg N/ha and mm of the r.ainfal1. REFERENCES 1. Black, C.A. (1965). Crop yieldg in relation to water supply and soil fertility.' Book "plant environment and efficient water use", cap. 9: Ed. by American Soc. of Agronomy. 2. Fogliata, F.A. and Dip R.A. (1971). Relacibn entre luvias, producci6n de caiia de az6car v fertilizacibn nitroaenada. - Rev. ndustrial y - Agricola - de TucumLn 48(1): Fogliata, F.A. (1974). Sugarcane irrigation in Tucumfin. Proc. SSCT 15: i

8 1424 AGRONOMY PRODUCCON DE CARA DE AZUCAR EN FUNCON DE LLUVAS Y FERTLZACON NTROGENADA F.A. Fogliata y C.A. Gargiulo RESUMEN En la provincia de Tucuman en Argentina, la cafia de azucar se siembra en Areas sin riego y el nitr6geno es el abono principal. Con el fin de establecer 10s t6rminos reales de interacci6n de lluvia y nitrdgeno, 13s mejores combinaciones entre 10s dos parametros estan bajo estudio en dos de las principales variedades de cafia de azucar.