Dynamics of sugar cane harvest residue decomposition

Paper presented at the XVIII Congress of the International Society of sugar cane Technologists, Sao Paulo, Brazil, 24-27 june 2013 and published here with agreement of the Society

Resumen

ABSTRACT

           After green cane harvesting, between 6 and 30 tons of dry matter per hectare of trash remains in the field. The aim of this paper was to evaluate the dynamics of sugarcane residue decomposition, and to study nutrient release from harvest residue. The trial was conducted in Tucumán-Argentina. The soil was a typical Haplustol. Sugarcane varieties LCP 85-384 and RA 87-3 were used in the trial, which lasted from 2008 to 2012. Every 25-35 days we evaluated: 1) quantity of residue (fresh weight and dry weight), and 2) C/N ratio in the residue. Besides, at the beginning and end of each cycle we evaluated P and K contents in the residue. In the four crop cycles considered (ratoon 1 to ratoon 4), the amount of residue left on the ground, expressed as tons of dry matter per hectare, was high. In LCP 85-384, initial trash amount ranged from 11.6 t/ha (ratoon 3) to 15.2 t/ha (ratoon 2), whereas decomposition percentages varied between 43% and 59% in a period of 260 to 323 days. In RA-87-3 initial trash amount ranged from 12.5 t/ha (ratoon 4) to 18.1 t/ha (ratoon 1), with decomposition percentages between 36% and 60% for a period of 194 to 323 days. In general, fresh residue C/N ratios were high (over 60). Initial C/N ratio varied among the following values: 79.2 (2008/2009), 77.4 (2009/2010) and 68.8 (2010/2011), and 93.5 (2008/2009), 102.9 (2009/2010) and 60.5 (2010/2011) for LCP 85-384 and RA 87-3, respectively. Final C/N ratio ranged from 30.8 (2010/2011) to 31.9 (2008/2009) and 39.3 (2009/2010) for LCP 85-384, and from 29.9 (2010/2011) to 33.9 (2008/2009) and 43.4 (2009/2010) for RA 87-3. This represented a reduction in at least 50% in all situations studied. Trash initial C concentration, expressed as percentage of dry matter, amounted to values between 42% and 45.5%, and between 38.8% and 47.5% in LCP 85-384 and RA 87-3, respectively. Residue initial N concentration varied between 0.53% and 0.71% and between 0.43% and 0.66% in LCP 85-384 and RA 87-3, respectively. As expected, N contents were more variable than C contents. Trash final C and N concentrations ranged from 30.4% to 33.2% and from 0.84% to 1.00% in LCP 85-384, whereas these values varied from 27.8% to 34.5% and from 0.82% to 1.1% in RA 87-3. Residue initial P concentrations reached 0.05% and 0.07% in LCP 85-384, and 0.06% and 0.1% in RA 87-3. Final P concentration ranged from 0.06% to 0.08% in both varieties. Residue initial K concentrations were between 0.64% and 0.75% for LCP 85-384, and between 0.56% and 0.67% for RA 87-3, respectively. Final K concentration varied from 0.09% to 0.19% and from 0.11% and 0.19% for LCP 85-384 and RA 87-3, respectively. K release values were high, whereas P ones were generally low.

RESUMEN
Dinámica de la descomposición del residuo de cosecha de la caña de azúcar

          En este trabajo se estudió la dinámica de descomposición y la liberación de nutrientes del residuo de cosecha de la caña de azúcar. El ensayo se realizó en Tucumán-Argentina entre 2008 y 2012. Los cultivares empleados fueron LCP 85-384 y RA 87-3. Cada 25-35 días se determinó: 1) peso fresco y seco del residuo y b) relación C/N del residuo. Al inicio y fin de ciclo se evaluó el contenido de P y K del residuo. Para LCP 85-384 la cantidad inicial de residuo varió entre 11,6 y 15, 2 t/ha y la tasa de descomposición estuvo entre 43% y 59%. Para RA 87-3 la cantidad inicial de residuo estuvo entre 12,5 y 18,2 t/ha, con porcentajes de descomposición entre 36% y 60%. La relación C/N inicial del residuo fue alta, pero decreció significativamente durante cada ciclo agrícola. Los valores más elevados fueron 79,2, para LCP 85-384 (2008/09) y 102,9 para RA 87-3 (2009/10). La concentración inicial de C del residuo varió entre 42% y 45,5% y entre 38,8% y 47,5% para LCP 85-384 y RA 87-3. La concentración inicial de N estuvo entre 0,53% y 0,71% y 0,43% y 0,66% para LCP 85-384 y RA 87-3. La concentración de C decreció y la de N aumentó durante el transcurso de cada ciclo. El contenido de P del residuo no varió entre inicio y final de ciclo. El contenido inicial de K estuvo entre 0,64% y 0,75% (LCP 85-384) y entre 0,56% y 0,67% (RA 87-3). La liberación de K del residuo fue elevada. La cantidad de residuo que quedó después de la cosecha y la relación C/N del mismo fueron altas, pero ambas decrecieron significativamente durante el ciclo agrícola. La descomposición del residuo aportó cantidades variables de C, N y K, lo cual puede modificar las necesidades de fertilizantes en el mediano plazo.