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This study focused on alfalfa (Medicago sativa) to investigate the effect of partial root-zone drying irrigation (PRDI) on N-fixing crops available soil P. A three-year field experiment was designed with two irrigation methods and four irrigation volumes. Two irrigation methods consisted of PRDI and conventional furrow irrigation (CFI), and four irrigation volumes were set as 70% ETc (alfalfa water requirement), 85% ETc, 100% ETc and 115% ETc. This study showed that the PRDI had no effect on alfalfa seasonal forage yield but increased alfalfa P uptake. The PRDI decreased the soil available P content and stock but had no effect on the total P content and stock, which demonstrates that effect of PRDI on crop available soil P was different when different P forms were used to estimate crop available soil P. This study also showed that the variation in the coefficient was below 3% between soil P (available or total P) contents and soil P stocks, indicating that soil P contents and stocks were similar when estimating alfalfa available soil P under PRDI conditions. The findings of this study present a pattern of estimating the N-fixing crops available soil P in relation to PRDI. [ABSTRACT FROM AUTHOR]

The responses of soil P availability and cotton growth to biochar addition under different P supply levels are not well documented. Thus, a pot experiment was conducted to investigate the effects of biochar addition on soil nutrient status, microbial characteristics related to P cycling and cotton growth with or without adequate P supply. Biochar was added to soil grown cotton at three rates of 0, 3 and 30 t ha−1 under two P fertilizer levels of 0 and 150 kg P2O5 ha−1, respectively. Results showed that biochar addition had significantly positive effects on soil P availability, phosphate solubilizing bacteria number, phosphatase activities (except acid phosphatase activity), cotton nutrients uptake and seedcotton yield, regardless of P fertilization level. The magnitude of soil available P content increase after biochar addition with P fertilizer was greater than without P fertilizer. And 3 t ha−1 biochar was better than 30 t ha−1 biochar for converting soil P into available P. Under a given P fertilizer level, biochar addition had fertilizer-like diminishing effect on seedcotton yield. Conclusively, the co-application of P fertilizer and the appropriate amount of biochar could be beneficial for soil P availability in cotton production. [ABSTRACT FROM AUTHOR]

Winter wheat (Triticum aestivum L.) production in northwestern China as a monoculture is hampered by unfertile soil and drought. With the fast-developing Chinese chemical fertilizer industry, many farmers now use more nitrogen (N) fertilizer as topdressing for winter wheat in early spring, in addition to a basal dose of N fertilizer applied in the previous autumn at seeding time. The objective of this study was to evaluate the increase in grain yield of dryland winter wheat by early spring N fertilizer topdressing, and its relationship to soil moisture, available N, phosphorus (P) and potassium (K). Field experiments with no N fertilizer topdressing (Fb) and N fertilizer topdressing (Fb+t) treatments were carried out over two growing seasons at 54 site-years to assess the relationship between increase in winter wheat grain yield by early spring N fertilizer topdressing and soil moisture, available N, P and K in Changwu county, Shaanxi province, China. Compared to Fbtreatment, the Fb+ttreatment produced grain yields lower at 10 site-years, and increased by <10% at 21 site-years and by >10% at 23 site-years. The results indicated that topdressing N fertilizer could increase wheat grain yield when soil nitrate-N accumulation in the 0–20, 20–40 and 40–60 cm depths was less than 121.7, 36.4 and 24.1 kg N ha−1, and soil moisture content in the 40–60, 60–80 and 80–100 cm depths was more than 15.7%, 16.7% and 16.9%, respectively. The findings also suggested that it is not necessary to analyze soil for ammonium-N, available P and K before topdressing N fertilizer. It is necessary to analyze 0–60 cm soil profile for nitrate-N and 40–100 cm depth for soil moisture before topdressing N fertilizer for winter wheat in dryland areas of northwestern China. [ABSTRACT FROM AUTHOR]

Field-scale variation of soil phosphorus (P) information is very important for P fertilizer application and its soil sampling design in grassland. A total of 108 soil samples were collected from a long-term (41 years) grazed grassland P experiment field at Teagasc, Johnstown Castle, Wexford, Ireland, in March 2009. There were six P treatments (P0-0, P0-30, P15-15, P15-5, P30-30, and P30-0) since 1968, with changes since 1999. Each treatment had 6 replicate plots (a total of 36 plots, 3 soil samples per plot). The samples were analyzed for available (Morgan’s) P, potassium (K), magnesium (Mg), lime requirement (LR), and pH. The highest mean available P concentration was found in the P30-30 (30 kg P ha−1pre- and post-1998) plots, and the lowest mean available P concentration was found in the P0-0 (no P fertilizer since 1968) plots. Significant differences of mean P, Mg, LR, and pH values in different treatments were observed. There was a positive proportional effect for both the 36 plots and the 6 treatments for the P data: the local standard deviation increased with the increase of local mean. The proportional effect should be considered in order to optimize sampling design. Fewer samples can reflect soil P status in fields with low soil P levels, while more attention should be paid to the fields with high P levels in order to reduce environmental consequences of uniform applications. [ABSTRACT FROM PUBLISHER]

High rates of soil depletion, food insecurity, and poverty are widespread in western Kenya, which calls for urgent and affordable solutions. A field experiment was carried out during 2003 short rains and 2004 long rains in western Kenya to study the effectiveness of “PREP-PAC” on soil properties, maize (Zea mays L.), and legume yields of six maize–legume intercrops. The experiment was conducted in a randomized complete block design, with four replications and two levels of fertility (no fertilizer and PREP-PAC). The maize variety, cv ‘KSTP’ (94), was intercropped with six legume types, namely: Bambaranuts (Vigna subterranean L., Var. Dark brown), Soybean (Glycine max L., Var. TGX 14482E), Yellow grams (Vigna radiate L., local type), Groundnuts (Arachis hypogaea L., Var. Uganda red stripped), Beans (Phaseolus vulgaris L., Var. KK15), and Cowpeas (Vigna unguiculata L., Var. white type). The farm was characterized by low pH of 5.35, low soil available phosphorus (P) below the critical value of 10 mg P/kg, and generally low exchangeable cations. Results indicated a significant (P < 0.05) increase in soil pH, soil available P (P < 0.0001), maize and legume yields (P < 0.0001) throughout the cropping seasons. Intercrops with bambaranuts, beans, and groundnuts produced better legume yields compared to the rest of the legumes. Therefore, the authors of this study concluded that, PREP-PAC is effective with elevated N input (60 kg N ha−1) on restoring soil fertility and improving farm productivity in western Kenya. However, availability and accessibility of PREP-PAC in local markets needs to be improved. [ABSTRACT FROM PUBLISHER]

The heavy use of organophosphorus pesticides in northeastern China strongly affects the ecological functions and the quality of the soil environment. In this work, a 30-day soil incubation experiment was conducted to evaluate the potential of using soil available P and the activities of soil dehydrogenase and acid phosphatase as indicators of the application of methamidophos and glyphosate. Two kinds of unpolluted soils, phaiozem and burozem, were selected as the test soils. The higher application rate of organophosphorus pesticide to the two soils caused more release of PO4 3− which finally entered the soil available P pool, suggesting that soil available P is one of the effective chemical markers for biodegradation of organophosphorus pesticides. Methamidophos exhibited a significant inhibitory effect on the activity of soil dehydrogenase. The extent of enzyme inhibition was almost positively correlated with the insecticide concentration, and the enzyme activity was gradually restored after day 15. However, its effect on soil acid phosphatase activity (stimulation or inhibition) seemed to be indefinite, and varied with the application rate, soil type, and incubation time. In the case of glyphosate, soil acid phosphatase activity was depressed significantly and the depressing extent could be a function of herbicide concentration and incubation time, but soil dehydrogenase activity showed an irregular variation with the herbicide application rate and soil type. In general, dehydrogenase activity was a good biochemical indicator for the biodegradation of methamidophos, but for glyphosate biodegradation the indicator was acid phosphatase activity. [ABSTRACT FROM AUTHOR]