Can Sheep Control Invasive Forbs Without Compromising Efforts to Restore Native Plants?

Domestic sheep (Ovis aries) are increasingly being used to control non-native invasive plants in areas where restoration is a management goal. However, the efficacy of sheep grazing depends on both its potential for controlling undesirable plants and its ability to promote natives. To date, few studies have investigated impacts of sheep grazing on native forb recovery in North American grasslands. We assessed the impact of sheep on forbs by measuring the number of stems grazed before and after sheep foraged in western Montana, United States. Sheep grazed a higher percentage of non-native than native forbs (70% vs. 23%, respectively), and number of stems grazed was six times higher for non-natives than natives (48 vs. 5, respectively). Sheep preferentially selected the non-native forbs sulphur cinquefoil and yellow salsify over leafy spurge (fi = 2.075; fi = 0.969; fi = 0.969, respectively), as well as the native forbs white prairie aster (fi = 1.090) and blanketflower (fi = 1.000). Selection of native forbs was positively correlated with their pregrazing abundance and increased over the grazing period. Our findings indicate that when using sheep to control invasive forbs, appropriate timing and monitoring of grazing are critical for reducing nontarget impacts to native vegetation.     

Onion yield and quality response to two irrigation scheduling strategies

Irrigation technologies that conserve water are necessary to assure the economic and environmental sustainability of commercial agriculture. This study was conducted in the Rio Grande Valley in Texas to evaluate yield and quality of subsurface drip irrigated onions (Allium cepa L.) using different scheduling strategies and water stress levels. One strategy consisted of initiating irrigation when the reading of a granular matrix sensors (Watermark^{® 1} soil moisture sensor, Irrometer, Co., Riverside, CA) installed at 0.2 m depth reached −20 kPa (optimum), −30 kPa and −50 kPa. The second strategy was to replace 100%, 75%, and 50% of crop evapotranspiration (ETc) weekly. Higher total yields, and jumbo onion size yields were obtained when the soil moisture was kept above −30 kPa. Yields were not affected when water applications were reduced from 100% to 75% ETc and from −20 to −30 kPa. The ETc strategies of 100%, and 75% ETc resulted in similar water usage to the soil moisture monitoring strategies of initiating irrigation at −20 and −30 kPa. Total yields dropped significantly when soil water stress increased below −50 kPa. For the ET based strategy yields also dropped with the 50% ETc treatment. Onion bulb pungency and brix were unaffected by water level.     

Diurnal malate and citrate fluctuations as related to nitrate and potassium concentrations in tomato leaves

Abstract

Two experiments were conducted to determine if malate and citrate change diurnally, if these changes are light dependent, and how these changes relate to K⁺ and NO₃ ^?1 levels. Malate concentration in tomato leaves was shown to increase during the day and decrease at night. The inverse occurred with citrate. The dependency of the changes on light was demonstrated for malate, but not for citrate. A relationship with NO₃ ^? assimilation and K⁺ recirculation may explain the changes in malate concentration.     

The effect of micronutrients and gibberellic acid on the germination and metabolism of seedlings of themeda triandra forsk

Dormancy of the caryopsis of Themeda triandra Forsk was shown to be broken by the addition oí boron to the germination media. This effect was specific to boron, as no response was observed with zinc, copper, manganese, iron, cobalt and molybdenum in the germinating media. Evidence is put forward suggesting that dormancy is regulated by the stale of the endogenous boron in the caryopsis. It was found to stimulate the synthesis of RNA in the embryo and endosperm tissue, and also α‐amylase activity in both tissues, particularly the endosperm. The transiocation of the sugars from the endosperm to the embryo appears also to be regulated by boron. Gibberellic acid was also found to break dormancy, and to stimulate RNA synthesis and α‐amylase activity in the caryopsis.