Sprinkler-irrigated organic rice.

Sprinkler-irrigated organic rice SPANU Antonino1, BARRACU Francesco1 1 Dip. AGRARIA – Sez. Agronomia, Coltivazioni erbacee e Genetica - Università degli Studi di Sassari e-mail: tspanu@uniss.it Keywords: organic rice; sprinkler irrigation; preceding crop Introduction In the last ten years organic rice has occupied in Italy a very variable proportion of agricultural land. Organic rice is sold at the same prices of conventional one on Italian markets, but the average yield of 4.5 t ha-1 is lower compared to conventional rice yields, mainly as a consequence of the interdiction imposed by the Council Regulation 2092/91 on chemical fertilization and herbicide use on weed control. The insufficient availability of organic seeds also limits organic rice production. A long-term experimentation carried out in Sardinia lead to develop a sprinkler-irrigated technology (Spanu et al., 1992, 1996a, 1996b, 2004) instead of traditional continuous flooded irrigation systems. Sprinkler irrigated rice has demonstrated the possibility of producing grain yields as high as those of flooded rice, and showed many advantages: − energy saves, as precision land grading is not necessary; − use of tyre-weel machinery, with no specific modifications; − simpler control of weeds, with pre-emergence treatments; − inclusion in more favorable rotations with legumes, instead of traditional monocolture, to increase natural N and organic matter availability; − weeds can be mechanically controlled; − rice yields comparable with flooded rice; − save 40-50 % of water. This paper reports the results of three years research with the aim of increasing the production of rice seed for organic farming and for human use. Methodology Tree trials were carried out in the experimental fields of the University of Sassari (39°59’ N, 8°40’ E, 15 m asl). The soil has alluvial origin, was a medium clayey textured, Typic Eutric Haplic Fluvisol. Soil chemical properties are characterized by neutral pH (pH 7.3), absence of carbonates (3.2%), low total nitrogen (0.08 %) and organic carbon and by high phosphorus (43.0 ppm) and potassium (202.0 ppm) content. Water contents at field capacity and at permanent wilting point were those typical for this type of soil. A) In the first year Trifolium alessandrinum and T. subterraneum were compared as preceding crops for their effects on weeds and on soil nitrogen. As experimental design, a randomized block, with 3 replications were used for preceding legumes; each parcel area was 50 m2, sowing density of 400 germinable seeds m-2, and row distance of 14 cm. T. alessandrinum was ploughed into the soil whereas T. subterraneum was cut, one month and one day before rice sowing, respectively, and then N soil content was determined. Competitive ability of Trifolium against weeds was compared by several sampling in which fresh and dry weight of Trifolium and of each species of weeds were measured. The experiment was set up as a split-split plot with four replications. Two rice cultivars (‘Balilla’ and ‘Eurosis’) were assigned to the main plot and three sowing rates (300, 450 and 600 viable seeds m-2 with an inter-row distance of 0.14 m) to the sub-plots. The sub-sub plots received two nitrogen rates: 0 (green manure only) and 80 kg ha-1 of organic N (green manure plus 30 kg ha-1 at sowing and 50 kg ha-1 at stem elongation). Weeds were mechanically controlled using a spiked chain harrow. In the subsequent years a new set of trials was set up with green manure preceding rice sowing: B) four cultivars with T. Alessandrinum as preceding crop were compared (‘Balilla’, ‘Eurosis’, ‘Creso’ and ‘Selenio’); C) an additional trial was carried out with the cultivar ‘Eurosis’ to compare spontaneous fallow and green manure of T. alessandrinum. In this case soil and plants were sampled monthly to determine their nitrogen content. Nitrogen supply in trials B and C was provided by plowing preceding crops about one month before rice sowing, plus three N rates: D0 (green manure only), D80 and D160 of organic N after sowing (80 and 160 kg ha-1 respectively). An inter-row distance of 0.2 m was used with a sowing rate of 500 viable seeds m-2 to allow mechanical control of weeds, performed by a precision weeder. Plots were sown with a cone-seeder placing the seeds at a depth of about 3 cm. Water was applied according to Spanu et al. (2008). Irrigation was performed by sprinklers, depending of both evotraspiration (measured by Class A vessel “PAN”) and physiological stage. From sowing to complete emergence of rice were supplied 100 m3ha-1; during growth stages, irrigation water volumes were established replacing evotraspiration losses and providing a surplus according to coefficients: 0.4 (from emergence to tillering), 0.8 (tillering-stem elongation), 1.0 (stem elongation-earing), 1.2 (earing-cereous maturation), 0.9 (cereous maturation-physiological maturation). Water was applied when PAN evotraspiration exceeded 25 mm. Presence and developmental stage of weeds was periodically monitored for a correct timing of weeding. Measurements were made to determine main phonological stages, number of plants m-2 at emergence and harvest, number of fertile and sterile panicles per m-2, plant height and panicle length, kernel weight, percent of whole kernels and viable seeds. Results and discussion Meteorological parameters, characterized by no rain and high temperatures during rice crop cycle, showed no significant variations compared with means of last 50 years. Using spiked chain harrow in mechanical weed control was effective after T.alessandrinum, insufficient after T. subterraneum. Grain yield following T.alessandrinum was significantly higher than that following T.subterraneum for both cultivars, likely as a consequence of the greater N availability. Grain yield after T.alessandrinum was higher at the N rate of 80 kg ha-1 in both ‘Balilla’ (8.1 vs 6.8 t ha-1 N80 and N0, respectively) and ‘Eurosis’ (9.1 vs 8.2 t ha-1 N80 and N0, respectively), whereas no difference was detected between sowing rates or cultivars. Seed viability was always greater than 90%, with maximum values of 97%, positively affected by T. alessandrinum as preceding crop, and higher in cultivar ‘Euro’ than in’ Balilla’ (Spanu et al., 2007). In trials B and C, widening the inter-row distance to 0.2 m allowed an almost complete control of weeds by the ‘precision weeder’. Both cultivar and N rate affected grain yield: 6.6 t ha-1 were produced by ‘Balilla’ and ‘Selenio’ and 8.4 t ha-1 by ‘Eurosis’ at N0. At N160 all cultivars yielded more than 8 t ha-1, with a maximum of 9.7 t ha-1 for cultivar ‘Creso’ The only treatment affecting percent of whole kernels at the analysis of variance was the cultivar, with values of 65% for cultivar ‘Eurosis’, 68% for ‘Creso’ and greater than 70% for ‘Selenio’ and ‘Balilla’. Trial C showed T. alessandrinum as a preceding crop resulted in greater yields (8.4 t ha-1 at N0 and 9.5 t ha-1 at N160) compared to fallow (7.4 t ha-1 at N0 and 8.1 t ha-1 at N160) when cultivar Euro was utilized (Spanu et al., 2008). Mean percent of whole kernels was 65%, and seed viability was around 90% (Spanu et al., 2008). Fig. 1 shows total N content in soil and in rice plants measured during biological cycle in both fallow and Trifolium preceding crops. Soil N content derive advantage mosly by green manuring with T. alessandrinum (Fig. 1), although an addition of organic N fertilizer was needed to reach the highest yields. Probably, using multiannual legouminous plants like Medicago Sativa (L) it could be possible to allow a satisfactory N soil content as well as a more effective weed control, because of several mowing. Organic rice can take great advantage from sprinkler irrigation as it allows the use of a preceding crop like T. alessandrinum which can have positive effects on both weed control and N availability. Furthermore, sprinkler irrigation reduces environmental impact by reducing both water use - to about 8000 m3 ha-1- and energy use, due to the possibility of using tyre-wheel machinery and no need for precision land grading. Another advantage of sprinkler irrigation is the negligible arsenic and cadmium content of kernels compared to flooded rice, evidenced in a trial comparing 37 rice cultivars (Spanu et al., in press). A higher incidence of cancers and others diseases due to arsenic in rice is common in countries, like Bangladesh, where this cereal represents the basis of the diet ( Spanu et al., 2012a; 2012b). References Spanu A., Pruneddu G., Cabras P., Melis M., Spanedda L. - 1992 - Persistence and mobility in clay soil of different herbicides in sprinkler-irrigated rice (Oryza sativa L.). Agricoltura Mediterranea , Vol.122, 287-292. Spanu A., Pruneddu G., D'Andria R., Lavini L., Quagliettà Chiarandà F. – 1996a - Yield response of rice (Oryza sativa L.) to increasing sprinkler-irrigation volumes. ICID Journal, Vol. 45, N° 2, 55-66. Spanu A., Pruneddu G. - 1996b - The influence of irrigation volumes on sprinkler-irrigated rice (Oryza sativa L.) production. Agricoltura Mediterranea, Vol 126, n°4, 377-382. Spanu A., Pruneddu G. - 1997 - Effect of increasing nitrogen rates on the yield of sprinkler-irrigated rice (Oryza sativa L.). Agricoltura Mediterranea; Vol.127, n°4, 379-387. Spanu A., Murtas A., Ledda L., Ballone F. - 2004 – Innovative agronomic techniques for rice cultivation. Proceeding of the Conference “Challenger and Opportunities for Sustainable Rice-Based Production Systems” - Torino – Italy – 13-15 September. Spanu A., Murtas A. - 2007 - Produzione di semente certificata di riso destinata all’agricoltura biologica – Dal Seme, n.4. Spanu A., Murtas A. - 2008 -Tecniche agronomiche innovative per la produzione di semente certificata di riso (Oryza sativa L.) in regime biologico. In: Azioni di innovazione e ricerca a supporto del piano sementiero. Pag. 245 – 258. Spanu A., Murtas A., Ballone F. - 2009- Water Use and Crop Coefficients in Sprinkler Irrigated Rice.- Italian Journal of Agronomy, 2:47-58 Spanu A., Daga L., Orlandoni A.M., Sanna G. - 2012a – The role of irrigation techniques in Arsenic bioaccumulation in rice (Oryza sativa L.) - In corso di stampa. Spanu A., Sanna G. - 2012b – The role of irrigation techniques in Cadmium bioaccumulation in rice (Oryza sativa L.). - Atti di “International Cadmium Simposium” P.5 - Sassari – 8-9 giugno.