Ecological intensification of cereal production systems: Yield potential, soil quality, and precision agriculture

Wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) provide about two-thirds of all energy in human diets, and four major cropping systems in which these cereals are grown represent the foundation of human food supply. Yield per unit time and land has increased markedly during the past 30 years in these systems, a result of intensified crop management involving improved germplasm, greater inputs of fertilizer, production of two or more crops per year on the same piece of land, and irrigation. Meeting future food demand while minimizing expansion of cultivated area primarily will depend on continued intensification of these same four systems. The manner in which further intensification is achieved, however, will differ markedly from the past because the exploitable gap between average farm yields and genetic yield potential is closing. At present, the rate of increase in yield potential is much less than the expected increase in demand. Hence, average farm yields must reach 70–80% of the yield potential ceiling within 30 years in each of these major cereal systems. Achieving consistent production at these high levels without causing environmental damage requires improvements in soil quality and precise management of all production factors in time and space. The scope of the scientific challenge related to these objectives is discussed. It is concluded that major scientific breakthroughs must occur in basic plant physiology, ecophysiology, agroecology, and soil science to achieve the ecological intensification that is needed to meet the expected increase in food demand

The Phosphorus Nutrition of Two Grain Legumes as Affected by Mode of Nitrogen Nutrition

Two sand culture experiments were conducted to examine the effects of P stress, nodulation, and N source on the growth, dry matter distribution (DMD), and root development of soybean (Glycine~ (L.) Merr.). In both experiments two levels of nitrogen (O and 5.0 mM N) were employed to establish two contrasting modes of N nutrition: plants were either (1) solely dependent upon symbiotic N fixation, or (2) primarily dependent upon uptake of combined N from the nutrient solution. Total dry weight of N-fixing plants grown at optimal P levels was approximately 60% that of N-supplied plants. Mode of N nutrition had no effect upon the total dry weight of plants grown at deficient P levels. The DMD within the plant differed depending upon the P and N supply. Nodule dry weight of N-fixing plants grown at optimal P levels comprised 9% of the total plant dry weight and 61% of the root dry weight of 35 day old soybean. A decrease in the P supply inhibited nodule growth relatively more than either root or shoot growth. Nodule dry weight of N-supplied plants grown at optimal P levels comprised 2% of total plant weight and 15% of root dry weight and a decrease in the P supply affected shoot growth relatively more than either nodule or root growth. The higher yields of N-supplied plants resulted from increased early growth during the time when the plants not provided combined N were establishing an N-fixing, root-nodule system. When grown at suboptimal P levels, there was a similar partitioning of dry matter between the underground portion of the plant and the shoot in both N-fixing and N-supplied plants. However, the root:total plant dry weight ratio of N-fixing plants was significantly less than that of N-supplied plants. This difference was attributed to the larger nodule mass on N-fixing plants. There was an inverse relationship between nodule mass and total root length although the number of first-order lateral roots on nodulated and non-nodulated plants was the same. The data suggest that two functional equilibriums are operative in the N-fixing plant, namely, the partitioning of dry matter between (1) the underground portion of the plant and the shoot and, (2) the root and nodules. Phosphorus stress affected the root-nodule equilibrium relatively more than the partitioning of dry matter between the belowground and above-ground parts of the plant. In N-supplied plants, P stress primarily affected the partitioning of dry matter between the root and shoot. An N x P field experiment with a split-plot randomized block design was conducted to identify the critical external and internal P requirements of both soybean and cowpea (Vigna unguiculata (L.) Walp.) as affected by mode of nitrogen nutrition. Six P treatments were established in main plots on a Humoxic Tropohumult soil. Within each main plot an N deficient and N-luxuriant subplot was established: sugarcane bagasse was incorporated into the entire field at a rate of 16,000 kg/ha; N-deficient subplots received no urea-N applications while N-luxuriant subplots received applications of urea-N before planting and during crop growth totaling 1000 kg/ha. In vitro monitoring of the net N mineralization of incubated soil samples collected from N-deficient subplots during crop growth indicated that the bagasse immobilized most of the available soil N during the first seven weeks of crop growth and that plants in these treatments were predominantly dependent upon symbiotic N fixation to meet their N requirement for growth. Acetylene reduction activity and nodule dry weight of soybean and cowpea plants from N-luxuriant subplots sampled 32 and 46 days after emergence were less than 11% of their counterparts from N-deficient subplots grown at comparable P levels. This indicated that plants from the N-luxuriant treatments were primarily dependent upon uptake of combined N from the soil to meet their N requirement for growth. Results from the field experiment showed that soybean was more sensitive to low soil P than was cowpea. When grown without P or N fertilizer, soybean yielded 28% of the maximum yield obtained from optimal P treatments on N-deficient subplots while the comparable relative yield for cowpea was 72%. The sensitivity of N-fixing soybean to low soil P levels when grown on N-deficient soil could be characterized by: (1) a relative growth rate (RGR) which declined progressively throughout the crop growth period, (2) lower index tissue and seed P concentrations than the N-supplied soybean plants grown at comparable P levels although the critical internal P concentration required for 90% maximum yield of N-fixing and N-supplied plants was the same, (3) an external P requirement approximately 60% higher than N-supplied soybean plants and, (4) a relatively larger difference between the yield potentials of N-fixing and N-supplied plants than for cowpea. The tolerance of N-fixing cowpea to low soil P when grown on N-deficient soil could be characterized by: (1) a high RGR during the later stages of growth, (2) tissue P concentrations which were similar to those of N-supplied cowpea plants grown at comparable P-levels, (3) an external P requirement which was not affected by soil N availability and, (4) a relatively smaller difference between the yield potentials of N-fixing and N-supplied plants than for soybean. It was concluded that screening of grain legumes for tolerance to low soil fertility levels should be conducted on N-deficient soils to insure that nutrient requirements are assessed for the symbiotic, N-fixing plant

Changes in Cultural Practices of Farmers in Southeast Nebraska as a Result of Their Adoption of Transgenic Crops

How do cultural practices change as producers adopt transgenic crops? A group of progressive producers in southeast Nebraska were surveyed to learn how practices changed as RR soybeans were adopted. These producers were found conservative in changing their management practices to use transgenic crops most efficiently. Tillage and planting practices were unchanged from conventional crops. Seed dealers and on-farm research were the top educational resources used in determining which varieties of soybeans to plant. Based on this study, on-farm research offers Extension an avenue for providing needed information to producers

Can ratoon cropping improve resource use efficiencies and profitability of rice in central China?

Identifying cropping systems with small global warming potential (GWP) per unit of productivity is important to ensure food security while minimizing environmental footprint. During recent decades, double-season rice (DR) systems in central China have progressively shifted into single-crop, middle-season rice (MR) due to high costs and labor requirements of double-season rice. Ratoon rice (RR) has been proposed as an alternative system that reconciliates both high annual productivity and relatively low costs and labor requirements. Here we used onfarm data collected from 240 farmer fields planted with rice in 2016 to evaluate annual energy balance, environmental impact, and net profit of MR, DR, and RR cropping systems in central China. Energy factors, emission values, and commodity prices obtained from literature and official statistics were used to estimate energy balance, GWP, and economic profit. Average annual yield was 7.7, 15.3. and 13.2 Mg ha−1 for MR, DR, and RR systems, respectively. Average total annual energy input (36 GJ ha−1), GWP (9783 kg ha−1), and production cost (3057 $ha−1) of RR were 35–48$ ha−1) than MR. Compared with DR, RR produced statistically similar net energy yield while doubling the net economic return, with 32–42% lower energy input, production costs, and GWP. Consequently, RR exhibited significantly higher net energy ratio and benefit-to-cost ratio, and substantially lower yield-scaled GWP than the other two cropping systems. In the context of DR being replaced by MR, our analysis indicated that RR can be a viable option to achieve both high annual productivity and large positive energy balance and profit, while reducing the environmental impact

Can ratoon cropping improve resource use efficiencies and profitability of rice in central China?

Identifying cropping systems with small global warming potential (GWP) per unit of productivity is important to ensure food security while minimizing environmental footprint. During recent decades, double-season rice (DR) systems in central China have progressively shifted into single-crop, middle-season rice (MR) due to high costs and labor requirements of double-season rice. Ratoon rice (RR) has been proposed as an alternative system that reconciliates both high annual productivity and relatively low costs and labor requirements. Here we used onfarm data collected from 240 farmer fields planted with rice in 2016 to evaluate annual energy balance, environmental impact, and net profit of MR, DR, and RR cropping systems in central China. Energy factors, emission values, and commodity prices obtained from literature and official statistics were used to estimate energy balance, GWP, and economic profit. Average annual yield was 7.7, 15.3. and 13.2 Mg ha−1 for MR, DR, and RR systems, respectively. Average total annual energy input (36 GJ ha−1), GWP (9783 kg ha−1), and production cost (3057 $ha−1) of RR were 35–48$ ha−1) than MR. Compared with DR, RR produced statistically similar net energy yield while doubling the net economic return, with 32–42% lower energy input, production costs, and GWP. Consequently, RR exhibited significantly higher net energy ratio and benefit-to-cost ratio, and substantially lower yield-scaled GWP than the other two cropping systems. In the context of DR being replaced by MR, our analysis indicated that RR can be a viable option to achieve both high annual productivity and large positive energy balance and profit, while reducing the environmental impact

In-season Prediction of Attainable Maize Yield Using the Hybrid-Maize Model

The Hybrid-Maize Model Real-time Simulation and Yield Forecasting Case Study 1: Irrigated Maize, Lincoln, Nebraska Case Study 2: Rainfed Maize, Oliveros, Argentina Case Study 3: Rainfed Maize, Mead, Nebraska Conclusions Reference

Prospects for Increasing Sugarcane and Bioethanol Production on Existing Crop Area in Brazil

This article assesses sugarcane yield gaps (YG) in Brazil to determine the degree to which production can be increased without land expansion. In our scenario assessments, we evaluated how much of the projected sugarcane demand to 2024 (for both sugar and bioethanol) can be satisfied through YG closure. The current national average yield is 62% of yield potential estimated for rainfed conditions (i.e., a YG of 38%). Continuing the historical rate of yield gain is not sufficient to meet the projected demand without an area expansion by 5% and 45% for lowand high-demand scenarios, respectively. Closing the exploitable YG to 80% of potential yield would meet future sugarcane demand, with an 18% reduction in sugarcane area for the low-demand scenario or a 13% expansion for the high-demand scenario. A focus on accelerating yield gains to close current exploitable YG is a high priority for meeting future demand while minimizing pressure on additional land requirements

Closing yield gaps for rice self-sufficiency in China

China produces 28% of global rice supply and is currently self-sufficient despite a massive rural-to-urban demographic transition that drives intense competition for land and water resources. At issue is whether it will remain self-sufficient, which depends on the potential to raise yields on existing rice land. Here we report a detailed spatial analysis of rice production potential in China and evaluate scenarios to 2030. We find that China is likely to remain self-sufficient in rice assuming current yield and consumption trajectories and no reduction in production area. A focus on increasing yields of double-rice systems on general, and in three single-rice provinces where yield gaps are relatively large, would provide greatest return on investments in research and development to remain self-sufficient. Discrepancies between results from our detailed bottom-up yield-gap analysis and those derived following a topdown methodology show that the two approaches would result in very different research and development priorities