No abstract

Improved topsoil structural quality is expected under no‐till farming, but soil physical constraints can develop under continuous no‐till. Our objectives were: to evaluate the properties of loam, silty loam, and silty clay loam soils under various management practices on a regional scale; to clarify the relationship between soil organic matter pools and soil physical properties; and to find a minimum set of topsoil properties to characterize trends established by tillage. Thirty‐nine loam, silty loam, and silty clay loam soils were sampled from cropped fields managed using conventional tillage (CT) and no‐till (NT) as well as six undisturbed soils (uncropped). The A horizon thickness did not differ among soil textural groups and was 4 cm thicker in uncropped soils. Total and particulate organic C were significantly affected by management (uncropped > CT = NT, P < 0.001). Soil structural instability of uncropped soils (0.317 mm) differed from CT soils (0.723 mm) but not from NT soils (0.573 mm). Soil structural instability was negatively related to total and particulate organic C, and no relation was found with the resistant organic C pool. Water infiltration rate was the only topsoil property affected by a significant texture × management interaction. Lower infiltration rates in NT silty soils were caused by platy structural forms with horizontal pores. Soil penetration resistance (0–5 cm) was 0.77 MPa higher in NT than in CT soils. A minimum set of topsoil properties to evaluate tillage management includes structural instability, total or particulate organic C, infiltration rate, and penetration resistance.

No abstract

The negative relationship between grain size (percentage >2.5 mm) and protein content usually observed in barley grain samples is attributed to the presence of thin grains. The objective of this study was to determine whether, in grain samples from a given environment, thin grains had a different protein content than plump grains. Grain samples from field experiments were analysed for grain yield, size and protein content of the whole sample and of four size fractions within each sample. Grain yield ranged from 1.5 to 6.5 mg ha À1 and grain protein (whole sample) ranged from 6.8 to 13.4 %. Most of the variation observed in protein content was explained by the ratio of nitrogen availability to grain yield. Within a grain sample, thin grains had more protein than plump grains (>2.5 mm) only when the protein content of the whole sample was high, that is, when the grain sample came from an environment with a high relative abundance of nitrogen. The fact that grain samples with low grain size tend to have high protein content is not due to the presence of a high proportion of thin grains, because thin grains do not always have more protein than plump grains.

No abstract

Plant leaf area affects both plant growth and yield. Although the effects of phosphorus and water availability on leaf area development have been studied as isolated factors, little work has been done on their possible interactions. A pot experiment was conducted to investigate the effects of both P and water availability on early leaf appearance and expansion in soft red winter wheat (Triticum aestivum L.), and to determine whether the effect of water deficit changes at each level of P nutrition and whether the soil water content affects plant P uptake. The soil was a Lonewood loam (fine‐loamy, siliceous, mesic Typic Hapludult), which had an available P level of 8.2 mg P kg−1 (Mehlich III). Additional P was applied at 0, 10 and 20 mg P kg−1 soil. Water treatments consisted of keeping soil‐water content at 80% (well watered) and 53% (stressed) of the 10 kPa soil‐water content. Plant development, leaf appearance and expansion, and stomatal resistance were measured during the experiment. At harvest (38 d after emergence), leaf area, aboveground biomass, and P concentration were measured. Phosphorus and water availability exhibited a significant interaction on tiller and leaf appearance, which were reduced by water stress but only at 0 applied P. As individual factors, P and water influenced different plant features. Lack of applied P decreased the rate of leaf appearance and, therefore, the final number of leaves and leaf area per plant. Water deficit reduced individual leaf area and, at 0 applied P, reduced rate of leaf appearance, number of simultaneously expanding leaves, and final number of leaves. Phosphorus uptake was increased only with added soil P, and not by water stress. The ability of plants to cope with mild water stress was enhanced by adequate P nutrition.

Rapeseed (Brassica napus) is a crop relatively tolerant to salt and sodium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of soil salinity or sodicity.Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three salinity levels (2.3 dS m-1; 6.0 dS m-1 and 10.0 dS m-1) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 and 44). The soil was kept near field capacity.As soil salinity increased, the K/Na and Ca/Na ratios in the tissues decreased markedly but yields and aerial biomass production were not affected. As soil SAR value increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na selectivities decreased. Plants could not maintain their Ca concentration in soil with a high SAR. The grain yield and biomass production diminished significantly in the highest SAR treatment. Our results are consistent with those showing detrimental osmotic effects of salts in Brassica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and biomass production. These results show that the effects of sodicity are different from those of salinity.

Accurate critical levels must be accompanied by predictive models on the amount of P required to increase P availability to a target value to obtain reliable P recommendations. We estimated, based on information on soil properties, the increase in soil available P after the addition of a unit of P (b coefficient) in an area of homogeneous although geographically distant soils. All 71 selected soils were noncalcareous, belonging to the Mollisol order and located in the Pampean Region (Argentina). Samples (0–20 cm) were incubated for 45 d after the addition of five doses of P. Soils were characterized for parameters related to soil P availability: pH, particle size distribution, organic C, total P, initial soil available P, and two P retention indices differing in the interaction period between the added P and the soil matrix (1 or 18 h). Obtained b values ranged from 0.27 to 0.74. Soils located at the northern area of the study region had higher b values (mean = 0.58) than southern ones (mean = 0.42). The best multiple regression model for estimating the b coefficient (R2 = 0.70) included initial soil P, a binary variable that accounts for the location of the soil, and the P retention index with the shorter interaction period. The strong effect of the geographic position of the soil on the estimation of the b coefficient led us to hypothesize about a possible role of the mineralogic characteristics of the parent material on P dynamics. Our results indicate that single independent variable models may not be enough to predict the b coefficient in homogeneous soils.