The Effect of Plant Density, Zinc Added to Phosphorus Fertilizer Sources and Location on Selected Yield Parameters of Soybean

Background: Soybean [Glycine max (L.) Merrill] is an annual herbaceous leguminous grain crop which is cultivated mainly for its oil and protein. The objective of the study was to determine the effects of plant density and zinc added to phosphorus fertilizer sources on soybean yield performance under different environmental conditions. Methods: A field trial was executed in two sites during the 2018/19 and 2019/20 summer planting seasons. The experimental design involved a 2 × 2 × 5 factorial fitted into a randomized complete block design (RCBD) with four replications. The experiment consisted of two plant densities, a lower plant density of 66 666 plants/ha and a higher plant density of 111 111 plants/ha. The five different types of fertilizer treatments were single superphosphate, monoammonium phosphate, zinc sulphate added to single superphosphate, zinc sulphate added to monoammonium phosphate and control. Result: The results showed that plant density has a significant effect (P less than 0.05) on soybean number of pods per plant and the field biomass yield. Soybean planted under lower plant density conditions produced a significantly larger number of pods per plant during both planting seasons, whereas higher plant density conditions resulted in a higher soybean field biomass yield during the 2018/19 planting season. It was observed that soybean treated with monoammonium phosphate had higher seed mass.

Regulation of Phosphorus and Zinc Uptake in Relation to Arbuscular Mycorrhizal Fungi for Better Maize Growth

Zinc (Zn) is an important micronutrient for plants, whose deficiency in alkaline soils creates hurdles in the achievement of optimum crop growth. Moreover, overuse of phosphorus (P) fertilizers often causes Zn immobilization in the soil. The employment of arbuscular mycorrhizal fungi (AMF) could be potentially environmentally friendly technology in this regard. Therefore, a pot experiment was conducted to assess the beneficial role of AMF (Glomus species) on maize under low and high P and Zn levels. Seven levels of Zn (0, 20, 40, 60, 80, 100 and 120 mg Zn kg−1 soil ZnSO4·7H2O) and three levels of P (0, 14.5, 29 and 58 kg ac−1 as single superphosphate) were applied with (M+) and without AMF (M−). The results showed that a high application rate of Zn (100 and 120 mg Zn kg−1 soil) restricted P translocation in plants and vice versa. Moreover, the nutritional status of mycorrhizal plants (AM) was better than non-mycorrhizal (NM) plants. AM plants showed a maximum positive response at 20 mg Zn kg−1 soil, or 29 kg P ac−1. In response to 20 mg Zn kg−1 soil, root colonization was maximum, which enhanced the maize nutrient concentration in shoots. In conclusion, AMF inoculation (M+) with P (29 kg ac−1) and Zn (20 mg kg−1) is efficacious for improving maize’s growth and nutrition. More investigations are suggested at the field level under different agroclimatic zones to ascertain whether P (29 kg ac−1) or Zn (20 mg kg−1) with AMF is the best treatment for maize growth optimization.

Comparative Study between Traditional and Nano Calcium Phosphate Fertilizers on Growth and Production of Snap Bean (Phaseolus vulgaris L.) Plants

Recently, nanofertilizers are being tested as a new technology, either for soil or foliar applications, to improve food production and with a reduced environmental impact. Nano calcium phosphate (NCaP) was successfully synthesized, characterized and applied in this study. A pot experiment was carried out in two successive seasons in 2016 and 2017 on (Phaseolus vulgaris L.) plants to obtain the best phosphorus treatments. The results were applied in a field experiment during the 2018–2019 season. Single superphosphate (SSP) at 30 and 60 kg P2O5 fed−1 and NCaP at 10%, 20% and 30% from the recommended dose were applied to the soil. Foliar application involved both monoammonium phosphate (MAP) at one rate of 2.5 g L−1 and NCaP at 5% and 10% from the MAP rate. The results of all experiments showed that NCaP significantly increased the shoot and root dry weights, the nutrient content in the shoot and root, the yield components, the nutrient concentration and crude protein percentage in pods of the snap bean plants compared with traditional P. The greatest increase was obtained from a 20% NCaP soil application in combination with a 5% NCaP foliar application. The present study recommends using NCaP as an alternative source of P to mitigate the negative effects of traditional sources.

A Poultry Litter-Derived Organomineral Phosphate Fertilizer Has Higher Agronomic Effectiveness Than Conventional Phosphate Fertilizer Applied to Field-Grown Maize and Soybean

Inadequate disposal of poultry litter (PL) may promote eutrophication of water bodies due to its high nutrient content, including phosphorus (P). Thus, recycling P from PL to produce organomineral fertilizer (OMF), reduces the dependence on finite mineral P reserves, and also reduces P losses from soil. In this context, a field experiment was carried out to assess the agronomic effectiveness of a granular PL-derived OMF applied to maize and soybean in a highly weathered tropical soil. OMF was compared to single superphosphate (SSP) at five P rates between 0 and 70 kg ha−1. The shoot dry weight (SDW) and grain yields of soybean and maize were affected by P rates; however, no difference between OMF and SSP was found. A similar trend was observed for soil P and P uptake. The leaf P content and soil pH were not affected by either P sources or P rates. Although there was no difference between OMF and SSP on the crop yields, OMF had the highest relative agronomic effectiveness based on the SDW. These results show that the production of granular OMF from PL is a viable alternative to conventional P fertilizers and reduces the dependence of mineral P reserves.

The resilience of soil organic carbon stocks under contrasting hill country pasture management practices

In 2020 we measured the stability of soil organic carbon (SOC) concentrations and stocks under contrasting hill country pasture regimes, by sampling three slope classes and three aspect locations on each of three farmlets of a long-term phosphorus fertiliser and sheep grazing experiment. The farmlets included no annual phosphorus (NF), 125 kg of single superphosphate/ha (LF), or 375 kg superphosphate/ha (HF) that has been applied on an annual basis since 1980. Results from the 2020 sampling event were added to previous results reported from soil samples collected in 2003 and 2014. The SOC concentrations in the topsoil (0-75 mm depth), ranging from 4.23 to 5.99% across all slopes and aspects of the farmlets, fell within the normal range (≥3.5 and <7.0%) required for sustaining production and environmental goals. A trend was shown for greater SOC stocks in the topsoil in the HF farmlet (34.0 Mg/ ha) compared with the other two farmlets (31.6 Mg/ha), but this trend was not evident in the deeper soil layers (75-150, 150-300, 0-300 mm). Under the current conditions, topographical features such as slope and aspect had a more profound influence on SOC stocks than management history.

Coupling effects of phosphorus fertilization source and rate on growth and ion accumulation of common bean under salinity stress

Many agricultural regions in arid and semiarid climate zone need to deal with increased soil salinity. Legumes are classified as salt-sensitive crops. A field experiment was performed to examine the application of phosphorus (P) fertilizer source and rate on growth, chlorophylls and carotenoid content, DNA and RNA content and ion accumulation in common bean (Phaseolus vulgaris L.) cultivated under salinity stress. An experimental design was split-plot with three replicates. The main plots included two P sources, namely single superphosphate (SP) and urea phosphate (UP). The sub-plots covered four P rates, i.e., 0.0, 17.5, 35.0, and 52.5 kg P ha–1. All applied P fertilization rates, in both forms, increased plant height, leaf area, dry weight of shoots and roots per plant, and total dry weight (TDW) in t ha−1. The highest accumulation of N, P, K+, Mg2+, Mn2+, Zn2+, and Cu2+ was determined in the shoot and root of common bean, while 35 kg of P per ha−1 was used compared to the other levels of P fertilizer. The highest P rate (52.5 kg ha−1) resulted in a significant reduction in Na+ in shoot and root of common bean. The response curve of TDW (t ha–1) to different rates of P (kg ha–1) proved that the quadratic model fit better than the linear model for both P sources. Under SP, the expected TDW was 1.675 t ha–1 if P was applied at 51.5 kg ha–1, while under UP, the maximum expected TDW was 1.875 t ha–1 if P was supplied at 42.5 kg ha–1. In conclusion, the 35.0 kg P ha–1 could be considered the best effective P level imposed. The application of P fertilizer as urea phosphate is generally more effective than single superphosphate in enhancing plant growth and alleviating common bean plants against salinity stress.

Growth and Yield Response of Groundnut (Arachis hypogea L.) to Inorganic Fertilisers at Luyengo, Middleveld of Eswatini

Groundnut is an important food and cash crop for smallholder farmers in Eswatini. However, its yield is very low partly due to poor soil fertility particularly calcium and phosphorus deficiencies associated with soil acidity. Thus, a field experiment was conducted to determine the effects of different inorganic fertiliser types on growth and yield of groundnut. The treatments were: a control with no fertiliser, [2:3:2 (22) at 300 kg ha-1], single superphosphate (100 kg ha-1), calcium nitrate (120 kg ha-1) and a combination of calcium nitrate (120 kg ha-1) and single superphosphate (100 kg ha-1). A randomised complete block design (RCBD) with three replications was used. Results showed highly significant (p<0.01) differences among the fertiliser types on most of the growth parameters recorded. At 90% flowering, significantly highest number of leaves per plant (48.3), the tallest plant (42.17 cm), the highest canopy width (41.47 cm), the highest number of branches per plant (6.57) and plant dry biomass per plant (20.6 g) were recorded for treatments with calcium nitrate followed by the application of combination of calcium nitrate and single superphosphate. Similarly, most of the yield components and yield were significantly (p<0.05) affected by the fertiliser types. Significantly highest numbers of total pods per plant (28.8), mature pods per plant (26.9), dry pod yield (950.6 kg ha-1), hundred seed mass (82.8 g), shelling percentage (70.6) and seed yield (671.6 kg ha-1) were recorded from a combination of calcium nitrate and single superphosphate fertiliser. Thus, combined application of 120 kg ha-1 calcium nitrate and 100 kg ha-1 single superphosphate fertilisers can be used to increase the productivity of groundnut in the study area.

Occurrence of arbuscular mycorrhizal fungi spores in soils of some legumes and their response to varying concentrations of phosphorus application

A potted experiment arranged in a 5 × 3 factorial in a randomized complete block design was undertaken to investigate the occurrence of arbuscular mycorrhizal fungi (AMF) in the soil of five leguminous plants: Cajanus cajan (L.) Huth, Centrosema pascuorum Martius ex Benth, Crotalaria ochroleuca G. Don, Lablab purpureus (L.) Sweet and Mucuna pruriens (L.) DC. The effects of varying phosphorus concentrations (P0) (0 kg/ha of single superphosphate), P1 (100 kg/ha of single superphosphate) and P2 (200 kg/ha of single superphosphate) on the population of AMF spores under these legumes were also carried out. The AMF spores in soil samples were extracted at 19 weeks after planting, using the wet sieving and decanting method, and enumerated with the aid of a stereoscopic microscope. Spores of different species of genera Glomus and Gigaspora were encountered in the soils of the five leguminous plants. Spores of Glomus species predominated while the spores of Gigaspora species were found in lower numbers. The total AMF population was significantly affected by legume species (p ≤ 0.05). The total AMF spore counts were higher in the soils of Mucuna pruriens and Crotolaria ochroleuca (p ≤ 0.05). The populations of Glomus mossae in soils decreased with increasing level of applied phosphorus (p ≤ 0.05). A positive correlation was recorded between the total AMF spores, the predominant AMF spores and soil pH, while the organic matter content and the available phosphorus were negatively correlated with both the total AM spores and the predominant AMF spores.

Application of Single Superphosphate with Humic Acid Improves the Growth, Yield and Phosphorus Uptake of Wheat (Triticum aestivum L.) in Calcareous Soil

In calcareous soil, the significant portion of applied phosphorus (P) fertilizers is adsorbed on the calcite surface and becomes unavailable to plants. Addition of organic amendments with chemical fertilizers can be helpful in releasing the absorbed nutrients from these surfaces. To check out this problem, a field experiment was conducted for two years to determine the effect of P fertilizers and humic acid (HA) in enhancing P availability in soil and their ultimate effect on growth, yield and P uptake of wheat in calcareous soils. The experiment was comprised of five levels of P (0, 45, 67.5, 90 and 112.5 kg P2O5 ha−1) as a single superphosphate (SSP) and 2 levels of locally produced humic acid (with and without HA) arranged in a two factorial randomized complete block design (RCBD) with three replications. Wheat plant height, spike length, number of grains per spike, 1000-grain weight, grain, straw and biological yield were significantly improved by the addition of HA with SSP. Very often, the performance of 67.5 kg P2O5 ha−1 with HA were either similar or better than 90 or even 112.5 kg P2O5 ha−1 applied without HA. Post-harvest soil organic matter, AB-DTPA extractable and water-soluble P, plant P concentration and its uptake were also significantly improved by the addition of HA with SSP compared to sole SSP application. It was evident that P efficiency could be increased with HA addition and it has the potential to improve crop yield and plants P uptake in calcareous soils.