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Within-field variability of crop yield levels has been extensively investigated, but the spatial variability of crop yield responses to agronomic treatments is less understood. On-farm precision experimentation (OFPE) can be a valuable tool for the estimation of in-field variation of optimal input rates and thus improve agronomic decisions. Therefore, the objectives of this study were to investigate the spatial variability of optimal input rates in OFPE and the potential economic benefit of site-specific input management. Mixed geographically weighted regression (GWR) models were used to estimate local yield response functions. The methodology was applied to investigate the spatial variability in corn response to nitrogen and seed rates in four cornfields in Illinois, USA. The results showed that spatial heterogeneity of model parameters was significant in all four fields evaluated. On average, the RMSE of the fitted yield decreased from 1.2 Mg ha−1 in the non-spatial global model to 0.7 Mg ha−1 in the GWR model, and the r-squared increased from 10 to 68%. The average potential gain of using optimized uniform rates of seed and nitrogen was US$ 65.00 ha−1, while the added potential gain of the site-specific application was US$ 58.00 ha−1. The combination of OFPE and GWR proved to be an effective tool for testing precision agriculture's central hypothesis of whether optimal input application rates display adequate spatial variability to justify the costs of the variable rate technology itself. The reported results encourage more research on response-based input management recommendations instead of the still widespread focus on yield-based algorithms. [ABSTRACT FROM AUTHOR]

Global use of reactive nitrogen (N) has increased over the past century to meet growing food and biofuel demand, while contributing to substantial environmental impacts. Addressing continued N management challenges requires anticipating pathways of future N use. Several studies in the scientific literature have projected future N inputs for crop production under a business-as-usual scenario. However, it remains unclear how using yield response functions to characterize a given level of technology and management practices (TMP) will alter the projections when using a consistent dataset. In this study, to project N inputs to 2050, we developed and tested three approaches, namely ‘Same nitrogen use efficiency (NUE)’, ‘Same TMP’, and ‘Improving TMP’. We found the approach that considers diminishing returns in yield response functions (‘Same TMP’) resulted in 268 Tg N yr ^−1 of N inputs, which was 61 and 48 Tg N yr ^−1 higher than when keeping NUE at the current level with and without considering changes in crop mix, respectively. If TMP continue to evolve at the pace of past five decades, projected N inputs reduce to 204 Tg N yr ^−1 , a value that is still 59 Tg N yr ^−1 higher than the inputs in the baseline year 2006. Overall, our results suggest that assuming a constant NUE may be too optimistic in projecting N inputs, and the full range of projection assumptions need to be carefully explored when investigating future N budgets.

An experiment was conducted to test the hypothesis that the enhanced yield possible with grafted tomato ( Solanum lycopersicum L.) under field conditions will also increase the nitrogen (N) crop nutritional requirement (CNR). Determinate ‘Florida 47’ tomatoes were grafted onto interspecific hybrid rootstocks (‘Multifort’ or ‘Beaufort’) and grown in a sandy soil with six N rates (56, 112, 168, 224, 280, and 336 kg ha −1 ) under plastic mulched bed and drip-irrigation systems during the spring seasons of 2010 (March–June) and 2011 (April–July). The N-CNR for grafted and non-grafted tomatoes was assessed using five yield response functions: exponential, linear-plateau, quadratic-plateau, quadratic, and square root. Over the two seasons, the estimated N-CNR ranged from 165 kg ha −1 with the quadratic-plateau model to 324 kg ha −1 with the square root model. Confidence intervals (CI) around these N-CNR ranged from 125 to 585 kg ha −1 using the bootstrap method and from 98 to 440 kg ha −1 using the delta method. Analysis of these CIs gave N-CNR rates of 239–246 kg N ha −1 for grafted plants, and 196–197 kg N ha −1 for non-grafted plants. Predicted maximum marketable yields were similar between the models, ranging from 56 -71 Mg ha −1 for grafted plants, and 43–53 Mg ha −1 for non-grafted plants, over the two seasons. Overall, while the actual N-CNR is likely to vary with season, soil types, and management practices, the results indicated that grafted tomato plants had a greater N-CNR than non-grafted plants together with an increase in predicted marketable yield. The yield response curves also showed that at a fixed marketable yield goal within the estimated range, the N fertilization rate required was lower for the grafted tomato plants as compared with the non-grafted plants. This study demonstrated that N fertilization program for optimizing tomato production may be modified when grafted plants are used. [ABSTRACT FROM AUTHOR]

Climate change may lead to differences in the distribution of precipitation and to reduced water availability, with constraints on the cultivation of some crops. An analysis of vulnerability and of opportunities for adaptation is required for crops in areas where they are currently cultivated. The intra-specific biodiversity of crops is a significant resource for the adaptation of agriculture, but requires better knowledge of the responses of cultivars to environmental stressors. Simulation models of water flow in the soil-plant-atmosphere system can be coupled with future climate scenarios to describe the soil water regime, taking into account different irrigation scheduling options. The adaptive capacity of maize hybrids is evaluated in an irrigated district in Southern Italy. Two climate cases were studied: “reference” (1961–1990) and “future” (2021–2050). The model SWAP was run to determine the soil water balance for different irrigation levels. For each level the effectiveness of irrigation was evaluated by means of a performance indicator (IE). The Relative Evapotranspiration Deficit (RETD) was used as an indicator of water availability. The yield response to water availability of several maize hybrids was determined; their hydrologic requirements were thus defined and compared with the simulated values of RETD in response to climate and irrigation. Soil moisture regime and irrigation performance were also analysed. The adaptability of hybrids to the future water regime was assessed for different irrigation levels. The study indicated how, in the future climate case, the intra-specific crop biodiversity, in combination with cropping patterns better adapted to soil characteristics, may allow the current production system to be maintained. [ABSTRACT FROM AUTHOR]