SWEET SORGHUM PERFORMANCE AFFECTED BY SOIL COMPACTION AND SOWING TIME AS A SECOND CROP IN THE BRAZILIAN CERRADO

ABSTRACT Increasing attention has recently been given to sweet sorghum as a renewable raw material for ethanol production, mainly because its cultivation can be fully mechanized. However, the intensive use of agricultural machinery causes soil structural degradation, especially when performed under inadequate conditions of soil moisture. The aims of this study were to evaluate the physical quality of aLatossolo Vermelho Distroférrico (Oxisol) under compaction and its components on sweet sorghum yield forsecond cropsowing in the Brazilian Cerrado (Brazilian tropical savanna). The experiment was conducted in a randomized block design, in a split plot arrangement, with four replications. Five levels of soil compaction were tested from the passing of a tractor at the following traffic intensities: 0 (absence of additional compaction), 1, 2, 7, and 15 passes over the same spot. The subplots consisted of three different sowing times of sweet sorghum during the off-season of 2013 (20/01, 17/02, and 16/03). Soil physical quality was measured through the least limiting water range (LLWR) and soil water limitation; crop yield and technological parameters were also measured. Monitoring of soil water contents indicated a reduction in the frequency of water content in the soil within the limits of the LLWR (Fwithin) as agricultural traffic increased (T0 = T1 = T2>T7>T15), and crop yield is directly associated with soil water content. The crop sown in January had higher industrial quality; however, there was stalk yield reduction when bulk density was greater than 1.26 Mg m-3, with a maximum yield of 50 Mg ha-1 in this sowing time. Cultivation of sweet sorghum as a second crop is a promising alternative, but care should be taken in cultivation under conditions of pronounced climatic risks, due to low stalk yield

Chemical and physical-hydric characterisation of a red latosol after five years of management during the summer between-crop season.

Agricultural production systems that include the production of mulch for no-tillage farming and structural improvement of the soil can be considered key measures for agricultural activity in the Cerrado region without causing environmental degradation. In this respect, our work aimed to evaluate the chemical and physical-hydric properties of a dystrophic Red Latosol (Oxisol) in the municipality of Rio Verde, Goias, Brazil, under different soil management systems in the between-crop season of soybean cultivation five years after first planting. The following conditions were evaluated: Brachiaria brizantha cv. Marandu as a cover crop during the between-crop season; Second crop of maize intercropped with Brachiaria ruziziensis; Second crop of grain alone in a no-tillage system; Fallow soil after the soybean harvest; and Forest (natural vegetation) located in an adjacent area. Soil samples up to a depth of 40 cm were taken and used in the assessment of chemical properties and soil structure diagnostics. The results demonstrated that the conversion of native vegetation areas into agricultural fields altered the chemical and physical-hydric properties of the soil at all the depths evaluated, especially up to 10 cm, due to the activity of root systems in the soil structure. Cultivation of B. brizantha as a cover crop during the summer between-crop season increased soil water availability, which is important for agricultural activities in the region under study

Soil physical change and sugarcane stalk yield induced by cover crop and soil tillage

Conventional tillage and intensive machinery traffic are the major causes of physical soil degradation in sugarcane fields. This study evaluates the impact of adopting conservation management practices during sugarcane planting on soil physical properties and stalk yield of sugarcane in the municipality of Ibitinga, state of São Paulo, Brazil. The experimental design (split-block) included four cover crops and three soil tillage systems, with three repetitions. For comparison purposes, a control treatment was also included (without cover crop and under conventional tillage). Sampling for soil physical analysis was performed in three layers that coincide with soil horizons A (0.00-0.20 m), AB (0.20-0.30 m), and Bt (0.30-0.70 m), during cane-plant and first sugarcane ratoon cycles. The results showed that cultivation of sunn hemp associated with deep subsoiling induced high stalk yield of sugarcane in both production cycles, cane plant (116 Mg ha -1 ) and first ratoon (114 Mg ha -1 ), with a net gain of 11 and 9 Mg ha -1 compared with the control treatment, respectively. However, these results were not sufficient to induce significant differences in sugarcane yield. Nonetheless, the use of sunn hemp and millet, associated with subsoiling (at 0.40 or 0.70 m depth) during sugarcane planting, are promising management strategies to sustain better soil’s physical quality when compared to traditional management, conventional soil tillage without cover crops and/or cash crop, as peanuts, that increase the risks of soil compaction and physical degradation

Soil compaction on traffic lane due to soil tillage and sugarcane mechanical harvesting operations

Mechanical sugarcane harvesting increases soil compaction due to the intense traffic of agricultural machinery, reducing longevity of sugarcane crops. In order to mitigate the harmful effects caused by agricultural traffic on the soil structure in sugarcane fields, this study evaluated impacts of mechanical sugarcane harvesting on traffic lane under two soil tillage systems based on load bearing capacity models. The experiment was carried out in the region of Piracicaba, state of São Paulo, Brazil, on a Rhodic Nitisol, under conventional tillage (CT) and deep strip-tillage (DST). For CT soil tillage was applied to the entire area with a heavy disk harrow, at operating depths from 0.20 to 0.30 m followed by a leveling harrow at a depth of 0.15 m. For DST, soil tillage was performed in part of the area at a depth of 0.80 m, forming strip beds for sugarcane planting, while the traffic lanes were not disturbed. Undisturbed soil samples from traffic lanes were used in the uniaxial compression test to quantify preconsolidation pressure and to model the soil load bearing capacity. The surface layer (0.00-0.10 m) was most susceptible to compaction, regardless of the tillage system (CT or DST) used. In the DST, the traffic lane maintained the previous soil stress history and presented higher load bearing capacity (LBC) than the traffic lane in the CT. As in CT the soil was tilled, the stress history was discontinued. This larger LBC in DTS minimized the impacts of the sugarcane harvest. Under CT, additional soil compaction due to mechanical sugarcane harvesting in the traffic lane was observed after the second sugarcane harvest. There was a reduction in load bearing capacity from 165 kPa to 68 kPa under CT and from 230 kPa to 108 kPa under DST, from the first to the second harvest at surface layer. Water content at mechanical harvesting was the most relevant factor to maximize impacts on the soil structure in traffic lanes, for both tillage systems

Productivity and Quality Sugarcane Broth at Different Soil Management

The quality of sugarcane broth can be affected by soil management. In compacted soils the productivity is reduced, and the raw material is poor. This research aimed to evaluate productivity and quality of sugarcane for four soil management types: (CT) heavy harrow + light harrow; (CTI) Subsoiler + light harrow; (MT) Subsoiler and (NT) no soil movement. The variables investigated were resistance to soil penetration (SPR), the chemical raw material quality (broth) and crop yield. In crop rows, SPR did not reach severe levels up to 0.3 m for sugarcane root development. However, below this layer, MT, NT, and CTI reached SPR limiting values of 2.50, 2.35 and 1.95 MPa, respectively. In inter-crop rows, compaction was concentrated in soil surface layers (0–0.3 m). In addition, all adopted managements presented SPR above the critical value (2 MPa). The soil preparation forms qualitatively affected the sugarcane broth, showing higher fiber and protein contents in NT, MT, and CT. The PS, Brix, TRS, and Pol were not affected by soil management. Still, higher absolute values were found in the NT, indicating an increase in broth quality when applying conservation management. The highest yields were obtained by reduced tillage (MT), surpassing the lowest yield management (NT) with an increase of 10.5 Mg ha−1