Optimal Harvest Moisture Content for Maximizing Mid‐South Rice Milling Yields and Returns

Abstract

A gronomy J our n al • Volume 10 8 , I ssue 2 • 2 016 701 R ice (Oryza sativa L.) is unique from other major row crops in the United States in that it requires postharvest milling before pricing. As a result, profi tability is based on both mass yield and kernel integrity. Broken rice (also called "brokens"), which is typically either ground into fl our or used in pet food, is currently valued at 68.5% of unbroken kernels, or head rice yield (HRY) (USDA-FAS, 2014). Studies have shown that although kernels of some rice cultivars are genetically more susceptible to breakage during milling, the rice moisture content (MC) at the time of harvest (HMC) and exposure to high nighttime air temperatures during critical stages of production can directly aff ect the ratio of unbroken rice (i.e., HRY) to broken rice on milling.Other studies indicate that fi ssures in the kernel will develop when rice at low MC (£15%) is exposed to conditions that cause the dry rice kernels to rapidly absorb moisture (Kunze and Prasad, 1978;Siebenmorgen and Jindal, 1986). Subsequently, fi ssures form within the rice kernel when internal stressors exceed the material tensile strength of the kernel. Th ese fi ssures are fault lines where the kernel breaks during milling, which in eff ect reduces the number of intact kernels and increases the associated number of brokens. Similarly, harvesting rice at a high MC (>22% for long-grain cultivars) also creates a large proportion of broken kernels as a result of milling a greater number of immature kernels (Siebenmorgen and Qin, 2005;Siebenmorgen et al., 2006;Bautista et al., 2007). Th ese immature kernels are typically thinner, weaker, and more susceptible to breakage during milling than fully mature kernels; thus, there is a convex relationship between HRY and HMC. Furthermore, Siebenmorgen et al. (2007) found that each rice cultivar and type (long grain, medium grain, and short grain) has a diff erent optimal HRY and MC that maximizes the HRY. Siebenmorgen et al. (1992) showed that signifi cant losses in HRY arise when long-grain rice in Arkansas is harvested at MCs <15% or >22%. However, maximizing HRY is not necessarily a profi t-boosting strategy because drying costs are a necessary component of profi tability, with the charges depending on the ABSTRACTRice (Oryza sativa L.) is unique from other major row crops in the United States in that it requires postharvest milling before pricing. As a result, profi tability is based on mass yield (paddy yield) and kernel integrity, or head rice yield (HRY). A common dilemma rice producers confront is the selection of a harvest moisture content (HMC) to begin harvesting. Although harvesting with a high HMC can improve HRY, it also increases drying costs at the mill. Conversely, harvesting with a low HMC can save in drying costs but decreases HRY due to fi ssuring. Th is study determines the optimal harvest HMC that maximizes net value, accounting for both HRY and drying costs per megagram of rice, considering genetic diff erences across cultivars and th...

Current Status and Future Prospects of Head Rice Yield

“…Other factors include grain moisture during harvesting and drying [14], and methods used to dry down the grain/paddy (hot air or infrared drying) [15][16][17] have a critical impact on head rice yield [14]. In addition, seasonal conditions have been linked to higher grain breakage during milling [18][19][20]. High day/night temperatures, especially during gametogenesis and early anthesis, result in substantial grain yield losses [9].…”

Integrating Climate and Satellite Data for Multi-Temporal Pre-Harvest Prediction of Head Rice Yield in Australia

“…To each of these methods, an extra stage was incorporated by differentiating predictions at the harvest date from those at the delivery stand, the latter including grain moisture measurements. Recognising the significant impact of grain moisture at harvest on HRY [34][35][36], this separation was designed to clarify the influence of late-season factors on HRY, independent of the dominant effect of harvest moisture.…”

“…In contrast, the negative impact of values exceeding the optimal NDVI range is expected to be related to crops harvested too early with an increased incidence of immature grains. These immature grains have reduced structural integrity and increased susceptibility to breakage during milling [36,60,61].…”