Grass–Legume Forage Systems Effect on Phosphorus Removal from a Grassland Historically Irrigated with Reclaimed Wastewater

The utilization of reclaimed wastewater is a suitable and sustainable approach to agriculture production in water-scarce regions. However, even though the wastewater is treated to reduce nutrient concentration such as phosphorus, the 10,600 to 14,006 m3 of water applied ha−1 year−1 on grass and alfalfa hay crops in Nevada can lead to soil phosphorus buildup over an extended period. This study evaluated the effectiveness of forage systems (FS) of monoculture grass, monoculture legume, and their mixtures on herbage accumulation, tissue phosphorus concentration, and quantity of phosphorus removed from a grassland under wastewater irrigation. The study was carried out at the Main Station Field laboratory in Reno, Nevada, USA. A total of 23 FS using tall fescue (Schedonorus arundinaceus (Schreb.) Dumort), alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) in monocultures or grass–legume mixtures (25:75, 50:50, and 75:25) based on seeding rate were used. The response variables were herbage accumulation (HA), tissue phosphorus concentration, and phosphorus removal. Forage systems means were considered different P ≤ 0.05. Herbage accumulation, tissue phosphorus concentration, and phosphorus removal differed among FS and year. Herbage accumulation was similar for the grass monocultures (10.5 Mg ha−1; SE = 1.1) and the majority of the grass–legume mixtures (9.0 Mg ha−1; SE = 1.1) but both systems had greater HA than legumes monoculture (4.3 Mg ha−1; SE = 1.1). The legume monocultures of alfalfa and white clover had the greatest phosphorus concentrations (10.9 g kg−1 dry matter; SE = 0.44) among all FS. Total phosphorus removed was least among legume monocultures (34.0 kg P ha−1; SE = 6.2) in this study and generally similar for grass monocultures (67.4 kg P ha−1; SE = 6.2) and grass–legume mixtures of 75:25 (61.7 kg P ha−1; SE = 6.2). Based on the response variables, agronomic, and environmental considerations a grass–legume mixture that includes 75:25 or even a 50:50 seeding rate ratio will be suitable options for phosphorus removal from phosphorus enriched grasslands in semiarid ecosystems that utilized wastewater for irrigation.

Effect of Phosphorus Levels on Soil Properties and Plant Tissues of Two Nerica Varieties

Phosphorus levels in the soil are easily fixed and rendered unavailable to plants even if they are found to be high and therefore, its influence on uptake of other nutrients such as nitrogen, and potassium cannot be overemphasized. In that view, an experiment was set out at KALRO-Mwea to investigate on the effect of phosphorus levels on soil properties and plant tissue nutrient contents of Nerica rice variety. The experiment was laid out in a Randomized Complete Block Design in split-split plot arrangement and replicated thrice. Two rice varieties (Nerica 11 and Nerica 4) formed the main plots and 4 phosphorus levels (0 kg P/ha, 25 kg P/ha, 50 kg P/ha and 75 kg P/ha) formed the sub plots. Highest net pH decreases of 0.20 and 0.22 units were recorded at 75 Kg haˉ¹ P2O5 in season 1 and season 2 respectively, while the lowest net decreases of 0.12 and 0.16 were elicited at 50 Kg haˉ¹ P2O5 treatment in season 1 and season 2 respectively. A net decrease was observed in all the CEC levels where phosphorus was applied in all the seasons in which the highest net decrease of 1.09 and 1.03 during season 1 and 2 respectively was elicited on the control treatment, while the lowest net decrease of 0.61 and 0.59 was elicited by the 50 Kg haˉ¹ P2O5 rate in season 1 and 2 respectively. There was an inverse relationship exhibited between the phosphorus level of applications and the soil phosphorus net decrease across the two seasons. The net decrease was highest at 0 Kg haˉ¹ P2O5 and increased significantly with increasing phosphorus rate. That content of soil nitrogen were low with a marginal increase recorded with application of phosphorus across the seasons. The highest net increase of 0.05% was observed at the 75 Kg haˉ¹ P2O5 rate and control in season 1 while the application rate of 50 Kg haˉ¹ P2O5 had the lowest net increase of 0.02% in season 2. Highest mean plant-tissue phosphorus of 62.05 ppm was recorded in Nerica 4 under 75 kg P/ha treatment. Highest plant tissue nitrogen of 0.686% and 0.713% for Nerica 4 and 11 respectively were elicited at 75 kg haˉ¹ P2O5 in season 1, whereas in season 2 the highest plant tissue nitrogen of 0.721% and 0.691% at 75 kg haˉ¹ P2O5 for Nerica 11 and 4 respectively was recorded. Application of phosphorous led to the highest plant-tissue phosphorus in both seasons indicating the importance of proper P fertilizer application where from this study 50-75 kg haˉ¹ P2O5 rate is recommended in rice growing.

Spatial estimation of foliar phosphorus in different species of the genus Coffea based on soil properties

Information underlying analyses of coffee fertilization systems should consider both the soil and the nutritional status of plants. This study investigated the spatial relationship between phosphorus (P) levels in coffee plant tissues and soil chemical and physical properties. The study was performed using two arabica and one canephora coffee variety. Sampling grids were established in the areas, and the points georeferenced. The assessed properties of the soil were levels of available phosphorus (P-Mehlich), remaining phosphorus (P-rem) and particle size, and of the plant tissue, phosphorus levels (foliar P). The data were subjected to descriptive statistical analysis, correlation analysis, cluster analysis, and probability tests. Geostatistical and trend analyses were only performed for pairs of variables with significant linear correlation. The spatial variability for foliar P content was high for the variety Catuai and medium for the other evaluated plants. Unlike P-Mehlich, the variability in P-rem of the soil indicated the nutritional status of this nutrient in the plant.

Substrate Acidification by Geranium: Temperature Effects

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of temperature on SPD. The first experiment tested the effect of four day/night temperature regimes (14 °C day/10 °C night, 18 °C day/14 °C night, 22 °C day/18 °C night, and 26 °C day/22 °C night) on substrate acidification. At 63 days after transplanting (DAT), substrate pH declined from 6.8 to 4.6 as temperature increased. Tissue phosphorus (P) of plants grown at the highest three temperatures was extremely low (0.10%–0.14% of dry weight), and P stress has been reported to cause acidification. It was not possible to determine if the drop in substrate pH was a singular temperature effect or a combination of high temperature and low P. To resolve this, a second experiment tested a factorial combination of the three highest temperatures from the first experiment and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate). Regardless of tissue P concentrations, which ranged from deficient to above adequate, substrate pH decreased with increasing temperature. At 63 DAT, in the 0.065 and 0.13 P treatments, tissue P was deficient and pH decreased with increasing temperature from 5.6 to 4.7 and 5.9 to 4.7, respectively. In the 0.26 P treatment, tissue P was adequate at the lowest temperature and there was no acidification. At the mid- and highest temperatures, tissue P was deficient and statistically equivalent, yet pH decreased to 5.2 and 4.7, respectively. In the highest P treatment, tissue P levels were unaffected by temperature, above adequate, and pH declined with each increase in temperature from 6.5 to 5.0. The results at 63 DAT once more showed that temperature acted independent of tissue P and caused geraniums to acidify the substrate. In the third experiment, the amount of acidity produced by roots of plants grown at the two highest temperatures used in the first two experiments was quantified. Plants grown at the higher temperature produced 28% more acid per gram dry root. The results herein indicate that high temperature can induce SPD by geranium.