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Europ. J. Agronomy 28 (2008) 579–585

Potassium cycling in a corn-brachiaria cropping system

R.A. Garcia, C.A.C. Crusciol, J.C. Calonego, C.A. Rosolem ∗Department of Crop Science, College of Agricultural Sciences, Sao Paulo State University, C.P. 237, 18603-970 Botucatu SP, Brazil

Received 8 November 2007; received in revised form 9 January 2008; accepted 10 January 2008

bstract

Growing corn mixed with forage crops can be an alternative for pasture and mulch production during relatively dry winters in tropical areas,aking no-till feasible in some regions. However, little is known about nutrient dynamics in this cropping system. The objective of the present workas to evaluate K dynamics in a production system in which corn was either grown as a sole crop or mixed with Brachiaria brizantha. In the secondear of the experiment, nitrogen rates ranging from 0 to 200 kg ha−1 were applied to the system. Dry matter yields and potassium contents in theoil, as well as residues and plants were determined at corn planting and harvest. Potassium balance in the system was calculated. Corn grain yield inixed crop responded up to 200 kg ha−1 N. The introduction of brachiaria in the system resulted in higher amounts of straw on the soil surface and

igher K recycling. Soil exchangeable K balance showed an excess K for both N rates only in the mixed system; however, when non-exchangeablewas also included in calculations, excess K was found in both mixed and sole corn systems. Large amounts of non-exchangeable K were taken

p in the system involving brachiaria, which showed a considerable capacity in recycling K, increasing its contents in the surface soil layer.2008 Elsevier B.V. All rights reserved.

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eywords: Nutrient cycling; Non-exchangeable K; Livestock-crop integration;

. Introduction

Livestock-crop integration has been proposed as a tool forromoting technological innovations in raising livestock as wells in remediating degraded pasture soils (Borghi and Crusciol,007). A system called “Santa Fe”, where cash crops and for-ge crops are mixed or intercropped, was proposed in BrazilKluthcouski et al., 2000). This system allows growing corn,oybeans, rice and sorghum mixed with forage species suchs brachiarias that have a deep root system and considerableolerance to water deficiency. In this system, the forage seeds planted deeper in the same planting row as the grain, andfter the cash crop is harvested, then the forage seed will growo fodder for animal use during the dry season. Later, foragetraw is left on soil surface as mulch, which is paramount forhe success of no-till systems. Research in the States of Goias,ahia and Mato Grosso has shown that yields of corn mixed with

rachiaria brizantha was reduced by less than 3%, thus validat-

ng the system (Kluthcouski et al., 2000). However, according toakelaitis et al. (2004), the knowledge of how the forage and the

∗ Corresponding author. Tel.: +55 14 3811 7161; fax: +55 14 3811 7102.E-mail address: rosolem@fca.unesp.br (C.A. Rosolem).

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161-0301/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.eja.2008.01.002

namic; No-till

ixed crop are affected by the competition for production fac-ors such as nutrient availability is important for pasture growthnd satisfactory grain production.

According to Sparks and Huang (1985), soil potassiumncludes K in solution, exchangeable K, non-exchangeable Knd structural K. In most tropical regions in Brazil, soil colloidsre formed mainly by organic matter, caolinite, iron and alu-inum oxides, and in these pedogenic conditions, exchangeable

otassium is the most important pool of the nutrient available tolants (Raij, 1991). However, Raij et al. (1996) have shown thatome of the soil non-exchangeable K and K from plant residuesay contribute significantly to crop mineral nutrition.Maintenance of crop residues covering the soil is one of

he key factors for the success of no-till systems, affecting soilertility and crop nutrient absorption efficiency. Oliveira et al.2002) reported that the main factors to be considered whenhoosing cover crop species and green manures are dry mat-er yield and the capacity to recycle nutrients. Grasses used asover crops are efficient in the extraction of potassium fromoil and in recycling it in crop rotation systems. Sazonowicz

nd Mielniczuk (1985) found that pearl millet reduced soilxchangeable K up to 40% in areas without K fertilization,nd up to 27% in fertilized areas. Simonete et al. (2002)bserved that, on average, ryegrass extracted 69% of the K added

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hrough the fertilizer regardless of the amount used, and that thispecies can extract the nutrient from initially non-exchangeableools.

In general, nutrient mineralization rate in plant residueseft on soil surface in no-till systems is similar to theecomposition rate of organic matter. However, K may belmost completely released from straw before tissue decom-osition because it is present in plant organs as an ionnd is not bound to organic compounds (Marschner, 1995).osolem et al. (2003) submitted residues of black oat,illet, sorghum, sun hemp, brachiaria and triticale to sim-

lated rain and observed considerable K concentrations inhe leacheate with values ranging from 7 to 24 kg ha−1 fort ha−1 of residue dry matter. In another experiment, Rosolemt al. (2006a) observed that, after simulating rain over pearillet residue and applying potassium fertilizer on soil sur-

ace, soil K increased down to 8-cm in the soil profile, inddition to its rapid transformation into non-exchangeableorms.

The amounts of nitrogen (N) needed to meet crop demandepend on crop species, environment and rotation system, andt is larger when there are only grass species in rotation. There-ore, grain-producing grasses (such as corn) and forage (suchs brachiaria) mixed crops in no-till systems may increase themount of N needed for proper growth and production. Fur-hermore, Corsi (1993) considers that N is the nutrient mostequired by forage crops and that it limits growth of tropicalrasses in limed soils well fertilized with phosphorus, increas-ng biomass production and improving forage nutritional value.n contrast, grasses favored by a large supply of N may present aigher demand of K due to the higher production of phytomass.he objective of our study was to evaluate K dynamics in theoil-straw-plant continuum as affected by nitrogen rates in pro-uction systems in which corn was grown either as a sole cropr mixed with the tropical forage B. brizantha.

. Materials and methods

The experiment was carried out at the College of Agricul-ural Sciences, Sao Paulo State University, Botucatu, Sao Paulo,razil, in an Oxic Argiudol with 630, 90 and 280 g kg−1 oflay, silt and sand, respectively. The experimental area is at40 m altitude, 22◦51′S and 48◦26′W. The climate is mesother-ic with dry winter; average annual precipitation is 1400 mm;

verage temperature in the coldest month is higher than 18 ◦Cnd in the hottest month is over 22 ◦C. Soil samples wereaken at planting and analyzed as in Raij et al. (2001) show-ng pH (CaCl2) 5.2, 31.6 g dm−3 of O.M., 16.4 mg dm−3 of

(resin), 42 mmolc dm−3 of H + Al, 3.4 mmolc dm−3 of K,8 mmolc dm−3 of Ca, 19 mmolc dm−3 of Mg and 62.6% ofase saturation.

The treatments consisted of two cropping systems (CS, cornole crop; CB, corn and B. brizantha-mixed crop) and four nitro-

en rates (0, 50, 100 and 200 kg ha−1) applied in the second yearf the experiment. The experimental plots were 8 m × 10 m withcorn rows 0.80 m apart from each other. During the first year,

he system was just implanted and N treatments were not applied.

cfqd

onomy 28 (2008) 579–585

n the dry season (mild winter), brachiaria was mowed at 30 cmhenever it reached 60 cm or more (the forage was not takenut of the plots).

In the second year, corn was planted along withrachiaria in November, 6 days after chemical desicca-ion of B. brizantha remaining from the dry season withlyphosate at 1.96 kg a.i. ha−1. Simple corn hybrid AG9010 with5,000 plants ha−1 and brachiaria cv. Marandu at 2.5 kg ha−1 ofiable seeds were used. Fertilizers were applied to corn accord-ng to standard recommendation for high yields (Raij et al.,996), using 20 kg ha−1 N, 39 kg ha−1 P and 50 kg ha−1 K asrea, simple superphosphate and potassium chloride, respec-ively. Brachiaria seeds were mixed with the fertilizer rightefore planting. Corn seeds were laid in furrows 3–5 cm deepnd the fertilizer/brachiaria mix was applied deeper (8–10 cm)n the same furrows. Nitrogen treatments were applied as urea0–30 cm away from corn rows and 3–5 cm deep in soil whenorn plants reached 6–8 leaves, at rates of 0, 50, 100 and00 kg ha−1.

Samples of the plant residues blanketing the soil sur-ace were taken when the brachiaria was killed and whenhe corn was harvested, 120 days after planting (DAP),sing wooden frames 0.50 m × 0.50 m distributed randomlyetween corn-rows. Three sub-samples were taken per plot.en whole corn plants were sampled at random at 120AP. At this time, the two center rows of each plotere harvested and used to determine grain yield. Grainumidity was standardized to 13%. Plant and plant residueissues were cleaned using an air jet, dried in a forced airven for 72 h at 60 ◦C, weighed, ground and wet digested.otassium contents were determined by Atomic Absorp-

ion Spectrometry after acid wet digestion (Malavolta et al.,997).

Soil samples were collected both at corn + brachiaria plant-ng (6 days after chemical desiccation) and at corn harvest.ix sub-samples were taken per plot from plant rows usingscrew auger down to 60 cm deep. Soil samples were dried,

round and sieved through 2-mm mesh. Exchangeable K wasxtracted using resin (Raij et al., 2001) and non-exchangeable

was heat-extracted with HNO3 1N (Knudsen et al., 1982).otassium balance in the system was calculated for exchange-ble and non-exchangeable K at harvest, using data from plotsith 0 and 200 kg ha−1 N. Inputs were soil K at planting, K

dded by fertilizers and K in plant residues on soil surface atrachiaria desiccation. Outputs were K accumulated in corn andn brachiaria, in plant residues on the soil surface and soil K athe time of harvest.

The experimental design was a complete randomized blockith a split-plot arrangement of treatments with four replicates.he two cropping systems were whole plots and nitrogen rates

0, 50, 100 and 200 kg ha−1) were applied in subplots. Originalata were submitted to ANOVA and the results of differentroduction systems (sole corn versus corn + brachiaria) were

ompared using LSD (P < 0.05). Regression analysis was per-ormed for N rates in each production system, and either linear oruadratic significant (F test, P < 0.05) equations with the highestetermination coefficients (R2) were chosen and fit to data.

R.A. Garcia et al. / Europ. J. Agronomy 28 (2008) 579–585 581

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ig. 1. Corn yields (A), Brachiaria dry matter yields at corn harvest (B), dry mD), amount of K in plant residues at corn planting (E) and harvesting (F), as aff�) Corn single; (�) mixed crop.

. Results

Corn grain yields response to N was quadratic irrespectivef brachiaria presence (Fig. 1A). As expected (Corsi, 1993),rachiaria responded up to 100 kg ha−1 N, despite the lowmount of dry matter produced while corn was growing, i.e.,41 kg ha−1 (Fig. 1B). Forage growth was slow in the mixedrop due to the presence of corn, but brachiaria biomass accu-ulation increased sharply after corn was harvested. By the time

orn was planted in the second year, the amount of plant residuesn soil surface was hardly affected by nitrogen fertilization, inoth systems (Fig. 1C). However, the mixed system had moretraw remaining from the dry season. The difference betweenhe systems decreased by the time corn was harvested, probablyue to the accelerated decomposition of plant residues (Fig. 1D).

The amount of K accumulated in the cover blanket on soilurface at the time of brachiaria desiccation was not affected byitrogen fertilization, but the presence of the forage mixed with

orn increased K accumulation in this pool compared with theole system (Fig. 1E). At corn harvest, K quantity in the straw,n both systems, showed a quadratic response to N rates, but theecrease in the mixed system was sharper.

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of the plant residue blanket on the soil surface at corn planting (C), harvestingby N rates. Asterisks (*) and (**) significant (P < 0.05 and 0.01, respectively).

As expected, a depth-dependent gradient was observed inxchangeable soil K contents (Fig. 2) and, regardless of nitro-en fertilization, exchangeable K contents in soil surface layersere higher in the mixed system (Fig. 2). Even in the absencef nitrogen (Fig. 2A), there was considerable recycling of

by brachiaria grown in the dry season, showing its highapacity to develop in adverse climatic conditions. As a resultf brachiaria roots growing deep in the soil profile, it wasbserved, in the mixed system, that K contents were low in the0–60 cm soil layer, for both N rates (Fig. 2A and D, respec-ively).

Soil K contents were similar under both cropping systemst corn harvest (Fig. 3). By the time corn was planted, thereas a high quantity of K in plant residues that washed into

he soil during the experiment, but 120 DAP (by the timef corn harvest), this K had not leached below 20 cm in theoil profile. There was also a large depletion of soil K inhe mixed system. The difference in soil K contents observed

n surface layers at planting (Fig. 2) decreased during plantrowth.

At planting, regardless of the amount of nitrogen fertil-zer, non-exchangeable K contents were lower in the surface

582 R.A. Garcia et al. / Europ. J. Agronomy 28 (2008) 579–585

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ig. 2. Soil exchangeable K by the time corn was planted as affected by croppingD). Horizontal bars show LSD in each depth (P < 0.05). (�) Corn single; (�) m

oil layers of the mixed system (Fig. 4). This shows thatrachiaria grown in the dry season extracted some of the ini-ially non-available forms of K. By harvest time, a decrease in

on-exchangeable K contents was observed in both the sole andixed systems, which had a bigger depletion, mainly in surface

ayers.

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ig. 3. Soil exchangeable K by the time corn was harvested as affected by croppi00 kg ha−1 (D). Horizontal bars show LSD in each depth (P < 0.05). (�) Corn single

ms and N rates. 0 kg ha−1 (A), 50 kg ha−1 (B), 100 kg ha−1 (C) and 200 kg ha−1

crop.

Exchangeable K balance in the sole system down to 60 cmn the soil profile, after 2 years of cropping, was negativerrespective of N fertilization. The K deficits for 0 (Fig. 5A)

nd 200 kg ha−1 N were 40 and 47 kg ha−1 (Fig. 5B), respec-ively, showing that some non-exchangeable K was taken up byorn. For the mixed system in the absence of N, 245 kg ha−1 K

ng systems and N rates. 0 kg ha−1 (A), 50 kg ha−1 (B), 100 kg ha−1 (C) and; (�) mixed crop.

R.A. Garcia et al. / Europ. J. Agronomy 28 (2008) 579–585 583

Fig. 4. Soil non-exchangeable K by the time corn was planted as affected by cropping systems and N rates. 0 kg ha−1 (A), 50 kg ha−1 (B), 100 kg ha−1 (C) and200 kg ha−1 (D). Horizontal bars show LSD in each depth (P < 0.05). (�) Corn single; (�) mixed crop.

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ig. 5. Exchangeable (A and B) and non-exchangeable (C and D) K balances i00 kg ha−1 (B and D). Vertical bars show LSD (P < 0.05).

as found in excess (Fig. 5A). In plots with 200 kg ha−1 N,he balance showed an excess of 101 kg ha−1 K in the mixedystem (Fig. 5B). However, when exchangeable K plus non-xchangeable K in soil down to 60 cm deep were considered,

balance after harvest was positive for both N rates. Wheno N was applied, an excess K of 268 kg ha−1 was foundn the sole system, and in the mixed it was 407 kg ha−1

Fig. 5C). With 200 kg ha−1 of N, the excess in the sole sys-em was 251 kg ha−1 K, and in the mixed system it decreasedo 283 kg ha−1 (Fig. 5D), showing a higher K requirement bylants with increased N rate.

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system by the time corn was harvested, as affected by N rates 0 (A and C) and

. Discussion

The present experiment confirms that brachiaria grownixed with corn does not affect grain yields, consistent withorghi and Crusciol (2007), where the 2-year average yieldf corn mixed with B. brizantha equaled that of the soleystem. Mixed production of grains and tropical forage is

ossible without significant effects on grain yields due tohe differential time and space in biomass buildup and nutri-nt acquisition of the species (Kluthcouski and Yokoyama,003).

5 J. Agr

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Potassium quantity in the straw at corn harvest, in both sys-ems, showed a quadratic response to N rates, with a sharperecrease in the mixed system, probably because K had washedut brachiaria residues by rain (Fig. 1F). Rosolem et al. (2005)eported that the amount of K leached following plant desic-ation is correlated with the nutrient contents in the residue,.e., the higher the K content, the higher the amount leachedut of the straw. As a result, exchangeable K contents in soilurface layers were higher in the mixed system (Fig. 2), proba-ly because the maintenance of live plants growing during thery season increased the amount of plant residues standing onoil surface at sampling (Fig. 1C). It has been observed thathe presence of cover crop species may increase nutrient sup-ly in surface soil layers (Fiorin, 1999). Potassium is highlyobile in plants at any concentration level, either within cells,

r in vegetal tissue, or in xylem or phloem, as it is not metab-lized in plants. It either forms easily reversible, large organicolecules or remains mostly in ionic form. Furthermore, this

on is the most abundant in plant cells (Marschner, 1995). Theelatively easy extraction of K from plant tissues was reportedy Moraes and Arens (1969), observing that the nutrient wasuickly washed out of plant leaves immersed in distilled water.his phenomenon may occur in field conditions due to dew or

ain. Therefore, cover crop residues are a significant source of, which may be increased in soil due to rain washing.Despite the large amount of K washed from vegetal residues,

utrient leaching was limited to the 5–10 cm layer, except forhe plots with 100 kg ha−1 N (Fig. 2C), whose K content inhe 10–20 cm layer reached 4 mmolc dm−3. However, the timerame between brachiaria desiccation and planting was short,nly 6 days. The retention energy of exchangeable cations asa2+, Mg2+ and K in soil colloids follows a lyotropic serieshere the first and main factor is the charge attraction energy

nd the second is the size of hydrated ions. Consequently, in well-rained soils, the relative cation amounts are affected by leachingnd other factors (Raij, 1991), and in general the amounts of Ca2+

re higher than those of Mg2+, which are higher than those of+. In an experiment by Rosolem et al. (2006b), soil columns

ontaining a sandy loam soil, with and without millet straw onhe surface and KCl fertilization, were submitted to simulatedain. Potassium leaching was observed to a depth of 4–8 cmn columns without plant residues on the surface, whilst theresence of straw limited K movement to 4 cm. In the presentxperiment, it could be observed in the mixed system, that asresult of brachiaria roots growing deep in the soil profile, K

ontents were low in the 40–60 cm soil layer for both N ratesFig. 2A and D, respectively).

There was much more K in the soil surface layers at plantinghan by harvest time (Fig. 2) in the mixed system. This largemount of K taken up in the mixed system was probably taken upy corn since brachiaria yielded only 341 kg ha−1 of dry mattern this system and no leaching was observed below 20 cm deep.herefore, the large supply of K observed at planting in the

ixed system was largely reused by corn plants up to 120 DAP.In highly weathered soils such as large tropical regions of

razil, exchangeable K in soil is the most important supply avail-ble to plants (Raij, 1991). However, it has been demonstrated

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hat non-exchangeable K may be absorbed in large amounts byeveral plant species in several types of Brazilian soils (Rosolemt al., 1988).

A negative balance of exchangeable K in the sole systemfter 2 years of cropping (Fig. 5B) clearly shows that some non-xchangeable K was taken up by corn. Conversely, in the mixedystem without N, K was found in excess (Fig. 5A), strong evi-ence of K being recycled through the forage grass grown in thery season.

This could be a consequence of the absorption of non-xchangeable K by brachiaria and/or K absorption from soilayers below 60 cm. The first hypothesis is more feasible becauseorn also had roots below 60 cm, and this result was not observedor the sole system. However, Pereira et al. (2004) pointedut that brachiarias present considerable root growth down to00 cm deep, an important factor in nutrient recycling. Accord-ng to Foloni and Rosolem (2004), K balance in no-till systemsith millet-soybean-black oat rotation depends more on K from

oil surface straw than on soil non-exchangeable K, which, inurn, is more important than K from fertilization, considering 2ears of K exhaustion.

In plots with 200 kg ha−1 N, in the mixed system, Kalance also showed an excess (Fig. 5B). This can be cred-ted to nutrient recycling by brachiaria grown during theinter. However, K excess was lower in this case, proba-ly due to the increased corn growth and K requirement.herefore, species capable of exploiting deep soil layersnd forming phytomass to sustain the no-till system areritical to minimizing K losses and maintaining soil fertil-ty.

Sparks (1987) reported that K in soil may also be classi-ed according to the time in which it is available for plants,

.e., readily available K (K in soil solution), quickly exchange-ble K, slowly exchangeable K and practically unavailable KK in the mineral crystalline lattice). Rosolem et al. (1996)rgue that the available classifications of soil K forms are arbi-rary and that they should correspond to K availability to plants.herefore, non-exchangeable K will not necessarily meet cornrequirements with proper synchronism.

. Conclusion

Potassium recycling in mixed cropping systems is verymportant for plant growth and to avoid losses down in theoil profile. However, it must be pointed out that if K rates arenderestimated in the fertilization program, soil K reserves maye depleted. A corn-brachiaria mixed crop was very effectiven recycling K, leading to increased exchangeable K contentsn the surface soil layers. Brachiaria was able to take up non-xchangeable forms of K in the soil, and this K, after cover cropesiccation, was washed out of plant residues and eventuallyore K was available for corn.

cknowledgement

This research was funded by FAPESP (The State of Sao Pauloesearch Foundation).

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