Sesame (Sesamum indicum L.) is an important oilseed crop, but is negatively affected by continuous cropping. There is still a lack of information on the effect of continuous cropping on soil chemical properties and mineral nutrition related to sesame growth and yield decline. Therefore, we investigated sesame growth and yield, nutrient concentration and soil chemical properties on five fields with continuous cropping history: non-continuous cropping (Year 0) and durations of two, four, five and six years on an upland field converted paddy in Tottori, Japan. Results show that plant height significantly decreased by 18.76%, 15.22%, and 13.64% in the Year 4, Year 5 and Year 6 fields, respectively, compared to Year 0. The effect of continuous cropping was more pronounced on the 1000-seed weight decline than seed yield. Compared to Year 0, seed yield decreased by 52.86% in Year 2 with no significant differences among the Year 2, Year 4, Year 5 and Year 6 fields, whereas the 1000-seed weight decreased by 6.68% and 12.20% in the Year 2 and Year 5 fields, respectively, compared to Year 0. Plant leaf tissue N concentration significantly decreased in the Year 2, Year 4 and Year 6 fields compared to Year 0, whereas leaf tissue K concentration decreased in the Year 6 field. The increase in duration of continuous cropping years gradually altered soil chemical properties. Soil pH, exchangeable Ca and Mg and cation exchange capacity (CEC) gradually increased in the long duration of continuous cropping, whereas total N and C, exchangeable NH4+-N, urease, dehydrogenase and catalase activities decreased. Our study suggested that the decrease in soil available N and enzyme activities, and decrease in K nutrition due to competitive ion effect as a result of increase in soil Ca and Mg could possibly contribute to the growth and yield decline of continuous sesame on upland field converted paddy.

Sesame is an important oilseed crop cultivated worldwide. However, research has focused on biochar effects on grain crops and vegetable and there is still a scarcity of information of biochar addition on sesame. This study was to assess the effect of biochar addition on sesame performance, with a specific emphasis on growth, yield, leaf nutrient concentration, seed mineral nutrients, and soil physicochemical properties. A field experiment was conducted on an upland field converted from paddy at Tottori Prefecture, Japan. Rice husk biochar was added to sesame cropping at rates of 0 (F), 20 (F+20B), 50 (F+50B) and 100 (F+100B) t ha −1 and combined with NPK fertilization in a first cropping and a second cropping field in 2017. Biochar addition increased plant height, yield and the total number of seeds per plant more in the first cropping than in the second cropping. The F+50B significantly increased seed yield by 35.0% in the first cropping whereas the F+20B non-significantly increased seed yield by 25.1% in the second cropping. At increasing biochar rates, plant K significantly increased while decreasing Mg whereas N and crude protein, P and Ca were non-significantly higher compared to the control. Soil porosity and bulk density improved with biochar addition while pH, exchangeable K, total N, C/N ratio and CEC significantly increased with biochar, but the effect faded in the second cropping. Conversely exchangeable Mg and its plant tissue concentration decreased due to competitive ion effect of high K from the biochar. Biochar addition is effective for increasing nutrient availability especially K for sesame while improving soil physicochemical properties to increase seed yield, growth and seed mineral quality.Agronomy 2019, 9, 55 2 of 20 (13.5%), ash (5%) [2], and mineral components, such as K (815 mg/100 g), P (647 mg/100 g), Mg (579 mg/100 g) and Ca (415 mg/100 g) [3]. This contributes to its health and nutritional benefits. Therefore, demand for sesame seeds is increasing due to the increasing knowledge on their dietary and health benefits, but there has been limited research on sesame evidenced by low yield in most growing areas hence hampering its adoption and expansion in the world [4]. Although sesame has been reconsidered a local specialty crop in Japan [5], the production of sesame is still low. For instance, the Food and Agriculture Organization (FAO) in 2016 estimated that 11 tons of sesame seeds were produced from an area of 21 hectares [6]. With the increase in abandoned paddy fields estimated at 360,000 ha by the year 2010, farmers were encouraged to convert such fields into cultivation of upland crops, such as wheat and soybeans [7,8], including sesame. However, crop yield on upland fields converted from paddy may decrease due to declining soil fertility status of the paddy soils that could require soil amendment with organic materials [9].Biochar is a soil amendment produced from thermal decomposition of organic materials through pyrolysis and it has the potential to increase crop yields [10,11]....

We evaluated the fatty acid compositions in relation to yield and soil nutrients from four fields A, B, C, and D with continuous monocropping histories of 0–3 years, respectively, in Japan from 2015 to 2016. Results showed that, in both evaluation years, seed yield did not significantly differ among the fields although field A produced the highest mean seed yield and 1000-seed weight. Between fields A and C, 1000-seed weight showed significant differences. The contents of seed-saturated fatty acids lauric and myristic decreased in only fields C and D whereas oleic, linoleic, and linolenic acids increased in field D. Only field A produced the highest contents of lauric and myristic acids whereas field D produced the highest contents of linoleic and linolenic acids. The soil total N and exchangeable K contents tended to decrease as exchangeable Mg content significantly increased on the fields with long duration of cropping, fields C and D. Principal component analysis revealed significant positive correlations between soil exchangeable K, and total N contents with 1000-seed weight and lauric acid, as exchangeable Mg content was related with oleic, linoleic, and linolenic acids. Therefore, the high oleic, linoleic, and linolenic acids from field D were mainly attributed to high soil exchangeable Mg content, whereas the high 1000-seed weight, lauric acid and myristic acid were due to the high soil exchangeable K content in field A. Overall, the fatty acid composition quality on the long-duration continuously monocropped fields could show high economic value at the expense of yield under this management practice in continuous monocropping.

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Sesame (Sesamum indicum L.) is one of the most ancient oilseed crops cultivated for its edible oil and uses in food. Sesame seeds are very nutritious and confer health benefits. However, its potential production in Uganda has not been fully realized. The objective of this review was to summarize the trends in sesame production, export quantity, export value, challenges, and strategies for sustainable sesame seed production in Uganda. The review revealed the sesame seed production and area harvested generally increased from 1996 to 2007 but significantly decreased between 2008 and 2018. The review also revealed that while the export quantities and values were low, they gradually increased from 2009 to 2016. The decreased production between 2008 and 2016 could have been due to challenges such as pests and diseases, loss of soil fertility, prolonged drought, poor agronomic practices, poor yielding varieties, and lack of access to credit. Therefore, it is recommended to improve breeding programs and soil management practices; strengthen agricultural credits and extension services to support marketing of sesame seeds; and improve agronomic practices and farmer knowledge on improved techniques such as sowing methods, plant spacing, intercropping practices, pests and disease control measures. These could boost sesame production in Uganda given the high domestic and global demand for sesame seeds and provide an opportunity to expand sesame production throughout Uganda. Research should focus on how to increase seed yield on farmers’ fields and bridge the yield gap between researchers and farmers while adopting good agronomic practices.

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Growth of sesame is known to be limited by poor K nutrition as a result of imbalance in soil exchangeable cations that cause a competitive ion effect in continuous monocropping from upland fields converted paddy. We hypothesized that balancing soil exchangeable cations will improve the K nutrition and growth of sesame plants. Therefore, the specific objectives of this study were to determine the effect of balancing soil exchangeable cations Ca, Mg, and K of continuously monocropped soils on the growth and cation uptake of sesame seedlings and also identify a suitable source of nutrients for improving K nutrition. A pot experiment was conducted under greenhouse condition in a 3 × 3 factorial design consisting of three levels of balancing treatments i.e. inorganic fertilizer for Ca, Mg, and K, rice husk biochar to increase K content, and the three durations of continuous monocropping soils of one year, two years, and four years from upland fields converted paddy. Balancing soil exchangeable cations was aimed at achieving optimal base saturations (CaO, 75%; MgO, 25%; and K2O, 10%). Results showed that balancing exchangeable cations did not significantly affect growth and cation uptake in the one and two-year soils but significant effect was observed in the four-year soil. Overall, plant height and dry weight increased for the balancing treatments of inorganic fertilizer K and rice husk biochar. Balancing exchangeable cations with biochar was more beneficial than with inorganic fertilizers. The four-year soil’s growth increase was attributed to an increase in K concentration and uptake due to the decrease in the soil Ca/K and Mg/K ratios to that of acceptable levels, which eliminated competitive ion effect as the soil K saturation increased above 5.0%, enhancing sesame growth. Therefore, a balanced soil exchangeable Ca, Mg, and K that eliminates a competitive ion effect will improve sesame growth and K nutrition although future research should focus on ensuring balanced cation rations under field conditions in continuous monocropping.