No abstract

China's vegetable production has experienced a rapid growth in recent years. Total production amounted to 522.7 million Mg (1 Mg = 10 g) in 2009, which was more than nine times that in 1980 and represented >50% of the world production. Meanwhile, excessive use of animal manures and chemical fertilizers in vegetable fields has brought various production and environmental challenges, including excessive accumulation of nutrients in soils and accelerated water pollution problems. In this study, we have evaluated the current status of phosphorus (P) in China's intensive vegetable production systems based on data summarized from nearly 100 publications plus results from our recent experiments. Gross overfertilization occurred in greenhouse (571 kg P ha) and open-field (117 kg P ha) vegetable systems compared with P removal in harvested crops (44 and 25 kg P ha) per season. Excess P input led to soil enrichment of labile P, measured as Olsen-P, averaging 179 (greenhouses) and 100 mg P kg (open fields) in the 0- to 20-cm soil depth, and in some cases led to P leaching, as evidenced by increases in Olsen-P and CaCl-P at the 40- to 60-cm soil depth. The vast majority of vegetable soils had Olsen-P exceeding the critical level (46.0-58.0 mg P kg) for optimum vegetable yield. Innovative policies and strategies are urgently needed to implement science-based nutrient management practices to attain sustainable vegetable production while protecting natural and environmental resources.

Application of readily soluble forms of N fertilizers to sandy soils may cause leaching of NO3‐N resulting in contamination of groundwater. The leaching loss of N may be reduced to some extent by using slow‐release forms of N. An intermittent leaching and incubation technique, to mimic natural occurrence of rainfall and dry conditions, was used to examine the leaching of N from readily soluble (NH4NO3) and slow‐release fertilizers [isobutylidene diurea (IBDU) and a polyolefin resin‐coated urea, Meister] in Wabasso (sandy, siliceous, hyperthermic Alfic Haplaquod) and Candler (hyperthermic, uncoated Typic Quartzipsamment) soils. After 29 d, the cumulative recovery of the applied fertilizer N in the leachate for the treatments decreased in the following order: NH4NO3 (88‐100%) > IBDU (27–32%) > Meister (11.5–11.7%). A significant portion (19.5–35.5%) of the total N leached from IBDU and Meister was in the urea form in the initial leaching; however, after 9 d, NO3 and NH4 forms represented the major portion of leachate total N. Although N from NH4NO3 was leached completely from the Candler sand, 12% of the applied N (as NH4NO3) was not recovered in the leachate from the Wabasso sand. Cumulative NH4‐N leached from the Wabasso sand was only 58% of that from the Candler sand. The results demonstrate that the amounts and forms of fertilizer N leached from the sandy soils depend on the solubility of the fertilizer, the soil type, and the duration of intermittent leaching.

No abstract

No abstract

A potato crop multimodel assessment was conducted to quantify variation among models and evaluate responses to climate change. Nine modeling groups simulated agronomic and climatic responses at low-input (Chinoli, Bolivia and Gisozi, Burundi)- and high-input (Jyndevad, Denmark and Washington, United States) management sites. Two calibration stages were explored, partial (P1), where experimental dry matter data were not provided, and full (P2). The median model ensemble response outperformed any single model in terms of replicating observed yield across all locations. Uncertainty in simulated yield decreased from 38% to 20% between P1 and P2. Model uncertainty increased with interannual variability, and predictions for all agronomic variables were significantly different from one model to another (P < 0.001). Uncertainty averaged 15% higher for low- vs. high-input sites, with larger differences observed for evapotranspiration (ET), nitrogen uptake, and water use efficiency as compared to dry matter. A minimum of five partial, or three full, calibrated models was required for an ensemble approach to keep variability below that of common field variation. Model variation was not influenced by change in carbon dioxide (C), but increased as much as 41% and 23% for yield and ET, respectively, as temperature (T) or rainfall (W) moved away from historical levels. Increases in T accounted for the highest amount of uncertainty, suggesting that methods and parameters for T sensitivity represent a considerable unknown among models. Using median model ensemble values, yield increased on average 6% per 100-ppm C, declined 4.6% per °C, and declined 2% for every 10% decrease in rainfall (for nonirrigated sites). Differences in predictions due to model representation of light utilization were significant (P < 0.01). These are the first reported results quantifying uncertainty for tuber/root crops and suggest modeling assessments of climate change impact on potato may be improved using an ensemble approach.

Phytotoxicity of copper (Cu) depends on the relative distribution of different chemical forms, which is a function of soil properties, such as soil pH and organic matter content. Sequential fractionation was conducted to partition the total Cu into exchangeable, sorbed, organically bound, precipitate, and residual forms. Three soils were sampled from existing citrus groves and 0 to 400 mg Cu kg−1 were added. The soils used were: Myakka fine sand (sandy, siliceous, hyperthermic Aeric Haplaquods; pH = 5.7), Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments; pH = 6.5), and Oldsmar fine sand (sandy, siliceous, hyperthermic Alfic Arenic Haplaquods; pH = 8.2). Phytotoxicity of added Cu was evaluated using citrus rootstock (Swingle citrumelo) seedlings grown for 330 d. In Cu‐unamended soils, the major portion of the total Cu was in the organically bound form in the low pH soils. However, in the high pH soil, the precipitate form was the dominant form. As the rate of Cu increased, the concentration of the readily soluble Cu forms (exchangeable + sorbed forms) increased in the low pH soils, that is, from 0.8 to 89.5 mg kg−1 (8.4–25.3% of total Cu) in the Myakka soil, and from 2.2 to 70.3 mg kg−1 (3.1–20.3% of total Cu) in the Candler soil. In the high pH Oldsmar soil, however, the concentration of readily soluble Cu forms increased only from 1.1 to 5.3 mg kg−1 In relation to the total Cu content this was equivalent to a decrease from 5.2 to 1.5%. The citrus seedling growth was negatively correlated with Cu concentrations in the readily soluble forms and positively correlated with those of the precipitate form. A 20% decrease in the top and root weights occurred at 2.5 mg kg−1 of readily soluble Cu in the Candler soil (pH = 6.5). The critical concentration was lower (1.7 mg kg−1) for root growth on the Myakka soil (pH = 5.7). The critical Cu concentration in the leaves varied from 60 to 68 mg kg−1, while that in the roots was 62 mg kg−1 in the Myakka soil, but increased to 270 mg kg−1 in the Candler soil. This study demonstrated that the readily soluble form of Cu is the most phytotoxic, and an increase in the precipitate form is, thus, responsible for a reduction in Cu phytotoxicity.

No abstract