Background: The standard method for grain moisture measurement is the conventional air oven-drying technique. This method requires a longer period of time to determine the moisture content (m.c.). Although electric moisture meters are popular in rice industries, it has to be calibrated frequently with the oven-drying method. Therefore, an alternative but fast and reliable method is required, especially, for the grain marketing industries. Results: Three different sizes of paddy (Oryza sativa L.) samples (Bg 300-intermediate bold, Bg 358-short round and At 405-long slender) were used for this study. Five different moisture levels (12–20% wet basis) were prepared by adding known amounts of water. Relationship between the microwave oven and hot air oven moisture values were evaluated using Pearson, Spearman and Kendall correlation coefficient methods. The linear regression relationship was also established between hot air oven and microwave oven moisture determination methods. According to the data, except for 870 W of absorbed MW power setting level, the other two MW power setting (265 W and 550 W) showed a significant statistical correlation (r > 0.55, P < 0.01) between the air oven and MW oven m.c. values of the three paddy samples. However, MW settings of 550 W for 7 min of absorbed power indicated a significantly higher regression coefficient of determination (r² = 0.94, P < 0.01) with air oven m.c. values. Conclusion: From the study, it can be concluded that the domestic microwave oven can be successfully used to determine the moisture content of different paddy varieties as an alternative method to the conventional air oven-drying method.

Potassium (K) is not easily assimilated into organic matter but helps to improve rice quality. Paddy yield and its quality depend on the correct time of fertilization and harvesting (days after flowering) in the field. Changes in the grain quality of (Oryza sativa L.) were studied in a field experiment over two dry seasons using three rates of muriate of potash (MOP; 60% K₂O) as 12.5, 25 and 37.5 kg/ha applied at the time of heading (7 weeks after planting—WAP). Paddy samples were harvested during 25, 30 (control), 35 and 40 days after 50% flowering (DAFF). Grain yield and physico-chemical characteristics of grain were studied after harvesting. The impact of seasons and treatments’ interactions was not statistically significant (P > 0.05) and, hence, data were averaged over two seasons. Length, breadth, true density and bulk density of rice grains were the highest with 37.5 kg MOP/ha applied at heading and harvested at 30–35 DAFF. Crude protein (6.24%) and crude fat (2.61%) contents in grains were the highest when harvested at 40 DAFF and 35–40 DAFF, respectively. Amylose content decreased with increased MOP rates at the time of heading and delayed paddy harvest. The highest average paddy yield (APY; 6.85 t/ha), head rice yield (HRY; 65%) and total rice milling yield (TMY; 67%) were recorded with 37.5 kg MOP/ha applied at heading of rice plant and paddy harvested at 35 DAFF. The APY, HRY and TMY were also 13.8, 7.7 and 5.9% higher, respectively, compared to the control. Applying K fertilizer at a rate 50% more (18.75 kg K/ha) than the recommended rate at the time of heading (7 WAP) and harvesting paddy at optimum maturity (35 DAFF), which is 5 days later than the recommendation, increase the yield and grain quality of direct seeded rice. Harvesting later than 35 DAFF resulted in a 10.5% loss of HRY (P < 0.05). The present study showed that K fertilizer applied at the rate of 37.5 kg MOP/ha at the time of heading 50% higher than the recommended rate is the best among K fertilizer treatments to obtain the highest HRY.