Contrasting yield responses at varying levels of shade suggest different suitability of crops for dual land-use systems. A meta-analysis.

Despite the large body of research studying crop growth parameters, there is still a lack of systematic assessments on how harvestable yields of different crop types respond to varying levels of shading. However, with the advent of agrivoltaic (AV) systems, a technology that combines energy and food production, and the new focus on agroforestry (AF), shade tolerance is becoming an important parameter for crop production systems. To address this research gap, a meta-analysis with data from two experimental approaches (intercropping and artificial shading with cloths, nets or solar panels) was performed to quantitatively assess the susceptibility of different temperate crop types to increasing levels of shading. Crop type specific yield response curves were estimated as a function of reduction in solar radiation (RSR), by estimating relative crop yields compared to the unshaded controls. Only studies that reported RSR and crop yield per area in temperate and subtropical areas were included. Using a random slope effect for each study, the specific variance components were accounted for. The results suggested a nonlinear relationship between achieved crop yields and RSR for all crop types. Most crops tolerate RSR up to 15%, showing a less than proportionate yield decline. However, significant differences between the response curves of different crop types existed: Berries, fruits and fruity vegetables benefited from shading up to RSR of 30%. Forages, leafy vegetables, tubers/root crops and C3 cereals showed initially less than proportionate crop yield loss. In contrast, maize and grain legumes experienced strong crop yield losses even at low RSR levels. The results provide first indicators for differences in crop type suitability to shading, and thus for AV and AF systems. Detailed yield response curves, as provided in this study, are valuable tools to optimize the output of annual crop components in AV and AF systems.

A Novel Approach to the Design and Analysis of Field Experiments to Study Variation in the Tolerance and Resistance of Cultivars to Root Lesion Nematodes (Pratylenchus spp.)

The root lesion nematode (RLN) species Pratylenchus thornei and P. neglectus are widely distributed within cropping regions of Australia and have been shown to limit grain production. Field experiments conducted to compare the performance of cultivars in the presence of RLNs investigate management options for growers by identifying cultivars with resistance, by limiting nematode reproduction, and tolerance, by yielding well in the presence of nematodes. A novel experimental design approach for RLN experiments is proposed where the observed RLN density, measured prior to sowing, is used to condition the randomization of cultivars to field plots. This approach ensured that all cultivars were exposed to consistent ranges of RLN in order to derive valid assessments of relative cultivar tolerance and resistance. Using data from a field experiment designed using the conditioned randomization approach and conducted in Formartin, Australia, the analysis of tolerance and resistance was undertaken in a linear mixed model framework. Yield response curves were derived using a random regression approach and curves modeling change in RLN densities between sowing and harvest were derived using splines to account for nonlinearity. Groups of cultivars sharing similar resistance levels could be identified. A comparison of slopes of yield response curves of cultivars belonging to the same resistance class identified differing tolerance levels for cultivars with equivalent exposures to both presowing and postharvest RLN densities. As such, the proposed design and analysis approach allowed tolerance to be assessed independently of resistance.

Pasture yield and soil physical property responses to soil compaction from treading and grazing—a review

This paper reviews animal treading and the associated effects on soil physical properties and pasture productivity from treading-induced soil compaction and pugging. Response curve relationships between soil physical properties (e.g. macroporosity, air-filled porosity, bulk density) and pasture and crop yield are reviewed. Optimum soil macroporosity for maximum pasture and crop yield ranges from 6 to 17% v/v, but there is a paucity of yield response curves for pastoral systems, particularly critical or optimum values of soil physical properties. There is little information available on the effects of cattle treading on soil physical properties and consequently pasture yield in seasons when soil pugging and poaching is minimised. Such information is needed to provide practical and rigorously tested decision support tools for land managers during grazing seasons. Knowledge of yield response curves, and critical or optimum values of soil physical properties for field pasture-based grazing systems, is required for improved farm-system production and economic decision support.

ETABLISSEMENT DE FONCTIONS DE PRODUCTION N-P-K POUR LE TABAC A CIGARETTE AU QUEBEC

Field fertilization tests were carried out with cigarette tobacco to determine production functions. Nitrogen was applied at rates of 0, 12, 27 and 40 kg/ha. Phosphorus was applied at rates of 0, 49, 73 and 122 kg/ha, and potassium at rates of 0, 93, 139 and 232 kg/ha. The nitrogen and potassium had a significant bearing on the yield. The yield response curves showed decreasing ratios. Yield predictions were developed to study the yield surfaces and economic optima. In order to obtain the least costly combinations of N and K, we found the equations of the marginal physical product, the isoquants for various yields and the isoclines. On the basis of the cost combinations and the optimum rates of application of N and K for various situations, we concluded that an economical and balanced fertilizer formula, as is currently recommended, should be used, but that the quantities of K could be increased in relation to the quantities currently recommended.

FERTILIZER RESPONSE OF FESCUE GRASSLAND VEGETATION

Fescue grassland vegetation at three locations in southwestern Alberta was fertilized with P, N, and N + P at various rates. Rates of application by an increasing-rate fertilizer spreader were from 0 to 1,120 kg N/ha and from 0 to 860 kg P/ha. Festuca scabrella Torr. responded to high rates of fertilizer whereas Danthonia parryi Scribn. did not respond. Yields were averaged across locations to show effects of fertilizers 1, 2, 3, and 4 years after application. Yield response curves showed that a residual effect persisted throughout the 4-year study period. Total yield was increased. Value of additional grazing compared with costs of purchase and application of fertilizer showed that fertilization of rangelands in the areas studied was not economically feasible.