No abstract

No abstract

No abstract

No abstract

No abstract

Maize (Zea mays) grain yield has been described to be particularly susceptible to environmental conditions around silking; however, a better temporal description of the effect of resource deprivation during this period is needed. Additionally, yield progress and the subsequent increase in the demand of assimilates may result in source limitation during the grain-filling period in current hybrids. This work assessed the effect of (i) short (~5 days) and intense shading stresses imposed at different times, and (ii) thinning during the effective grain-filling period, on yield components of an Argentinean, widespread hybrid. Grain yield was affected by resource availability during an extended period from ~300 growing degree-days (GDD) before silking to ~780 GDD after silking (base temperature = 8°C). Kernel number (KN) was reduced by shading treatments imposed within a relatively extended period of ~700 GDD centred on silking. Within this period, we establish a critical period of ~30 days around silking (i.e. –200 to 250 GDD after silking), in which KN susceptibility was maximal. The variation in KN during this period of 450 GDD was mainly accounted for by resource availability and not by timing of treatment imposition within this window. A direct relationship between KN and weight per kernel (KW) for shading treatments imposed from 0 to 200 GDD after silking indicated that compensation of KN reduction by KW increase might not be expected when stress occurred immediately after silking. Kernel number and KW presented an inverse relationship when shading took place after 200 GDD after silking. In addition, thinning after the onset of the effective grain-filling period increased KW. The results indicate that, even in the undisturbed crop, KW was limited by source capacity during grain filling. It is suggested that there is a need to reconsider current agronomic practices and breeding strategies, focusing on the source capacity during the grain-filling period.

Th e sunfl ower (Helianthus annus L.)-soybean [Glycine max (L.) Merr.] intercrop has emerged as an option that increases land productivity in the southern Pampas of Argentina, compared with sole crops, because of complementary use of resources between species. A common management practice for this intercrop consists of delay soybean sowing, although delayed planting reduces the capacity of soybean to capture resources. Simultaneous sowing could improve total intercrop productivity because of an increase in soybean grain yield with no or little detrimental eff ects on sunfl ower grain yield. Th e objectives of this study were to analyze the response of the sunfl ower-soybean intercrop and of their component species under diff erent sowing management (i.e., relay or simultaneous sowing) and water availability conditions. Th ree experiments were conducted at Balcarce, Argentina. Four cropping systems were evaluated: (i) sunfl ower-soybean intercrop with simultaneous sowing management (I00), (ii) sunfl owersoybean intercrop with 30 d of delay between sunfl ower and soybean sowing (I30), (iii) sunfl ower sole crop (SUN), and (iv) soybean sole crop (SOY). Sunfl ower-soybean intercrop grain yield tend to be higher than that for sole crops of the component species.Th is yield advantage for intercrop increased with water availability and was associated with an increase in intercropped soybean productivity. Intercrop sowing management had no eff ect on total intercrop grain yield. However, simultaneous sowing increased soybean contribution to intercrop yield. Finally, our results indicate that agronomic practices that promote intercropped soybean performance increase intercrop productivity relative to the sole crops of their component species.

The challenge to increase agricultural production with a minimum environmental impact requires to reach the maximum efficiency in the capture and use of resources such as photosynthetically active radiation (PAR), water, and nitrogen (N). Such requisites are encompassed in the ecological intensification (EI) concept. The aims of this work were to evaluate at a crop sequence level: i) crops yields, ii) water and radiation productivity and its components, i.e. resource capture and resource use efficiency, and iii) partial factor productivity of applied N (PFPN), partial nutrient balance for N (PNB), N uptake and N utilization efficiency of a two-year, three-crop sequence (wheat [Triticum aestivum L.]/soybean [Glycine max (L.) Merr.] double crop-maize [Zea mays L.]) carried-out under EI principles in comparison with the same crop sequence under current farmer practices (FP) in two contrasting locations of the Argentinean Pampas, i.e. Paraná (-31°50′;-60°31′) at the northern Pampas and Balcarce (-37°45′,-58°18′) at the southern Pampas. Experiments were carried-out during four consecutive years, covering two complete cycles of the crop sequence. For the accumulated grain production of the crop sequence, EI management outyielded FP from 13 to 42%, depending on environmental conditions. Maize yield accounted for most of the variation (41-64%) of the accumulated grain yield of crop sequence, whether in EI as in FP. Average grain yield differences between EI and FP treatments were 274 g m −2 for maize, 69 g m −2 for wheat and-2 g m −2 for soybean. Water and radiation productivities of the sequence were higher in EI than in FP (26% for water and 17% for radiation; P < 0.0001), mainly because of increases in resource use efficiencies. EI reduced partial factor productivity of applied N, but improved partial nutrient balance for N as compared with FP. These reductions in partial factor productivity of applied N were less than proportional than the increases in N rate. Moreover, in spite of the higher N rate in EI respect to FP, N utilization efficiency (N ut E), i.e. grain per unit N uptake, was higher across all situations in EI. Our results showed that the challenge to obtain high grain yields by increasing N rate in a medium-input system could be achieved even with an increase in N ut E. Grain yields improvements, and increases in radiation and water productivity were reached by applying a set of agronomic practices that included improved genetics, crop and fertilizer N management englobed under EI concept. Andrade, 2016; Cassman, 2017). Such requisites are encompassed in the ecological intensification (EI) concept defined by Cassman (1999, 2017). Decisions on agronomical practices based on EI concepts are oriented to closing the gap between water limited yield potential (Y w) and actual yield and improving natural resource and input productivities using a field-specific management according to Cassman (2017). Improving resource and input productivity is a key step towards sustainable intensification.