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Alternative nutrient management options have improved with many synergistic processes of spatial and temporal scale leading to sustained and stabilized productivity due to concerns over the irregular and uneven application of mineral fertilizers. However, understanding the productivity dynamics of biomass and yield in diverse nutrient management and crop rotation intensities is important. This study was conducted during the transitional period with conventional (CONV), integrated (INT), and organic (ORG) nutrient management under four crop diversification intensities in a dry zone of Sri Lanka. Mono-cropped rice (LOW) and a rice-maize rotation (HIGH) were the starting point. After 1 year, the intensity of diversification was increased by adding interseason sunnhemp (rice-sunnhemp-rice; MEDIUM and rice-sunnhemp-maize; VERY HIGH). The INT LOW system during the 1st cycle was very effective. Crop biomass (41%), final grain yield (28%), and rice equivalent yield (36%) increased with the ORG LOW system than at ORG HIGH system. In the 2nd cycle, there was a higher grain yield (54%) and a higher rice equivalent yield (53%) in the ORG HIGH than ORG LOW. The productivity under VERY HIGH rotation was similar in ORG, INT, and CONV towards the end of two-year study. Halving the amount of mineral fertilizers and compensating with organic fertilizers maintains the productivity of existing crops without losing their full reliance on mineral fertilizers. Increasing the diversity from rice mono-cropping to rice-sunnhemp-maize cropping system delivered better synergy by improving overall productivity and grain yields in the organic system. This provides details for new farming system designs combined with ecological and sustainable pathways.

Narrow Brown Leaf Spot (NBLS) caused by Cercospora janseana is a common disease of rice causing severe yield loss. In order to identify the factors favourable for disease development under field conditions, a study was carried out during the 2017/2018 Maha and 2018 Yala seasons. Effects of mineral N fertilizer, weed control, and seed rate on the incidence and severity of NBLS disease were determined. Two levels of mineral N, i.e., Department of Agriculture, Sri Lanka (DOF) recommended level and half of the DOF level were used with weedy and weed-free conditions, under four different seed rates, 100 kg/ha, 125 kg/ha, 150 kg/ha and 175 kg/ha. NBLS incidence was significantly higher (p<0.0001) in the Maha season compared to the Yala season. In the Maha season, mineral N fertilizer by weed interaction was significant on disease severity. In the Yala season, the disease incidence was significantly (p<0.05) higher in weedy conditions and fertilizer, weed and seed rate interaction and fertilizer and seed rate interaction were significantly (p<0.05) higher. The lowest disease severity was recorded in both seasons with the 100kg/ha seed rate, 100% fertilizer and weed-free conditions. When the weedy conditions prevailed in the field in Maha season, a disease severity scale value of 2 was observed at the highest frequency. Although only the weed condition affects NBLS incidence, it was found that the seed rate, fertilizer and, weed condition interaction was critical to control the severity of NBLS in paddy cultivation.

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